Freebies and tutorials make my day. While the attraction may seem obvious, I'll just elaborate: I love these online project tidbits, because they present the ingenuity of the DIY spirit in all its flying colors!
Tutorials are popping up all over the web. DIY tutorials are instructional lessons that lead the viewer through a series of step-by-step directions. Generally, a tutorial will include what materials are needed to make the project and the steps to make it from beginning to completion.
Going green at home doesn't have to drain your bank account. With some recycling, repurposing and creative resourcefulness, it is easy to create useful and decorative green items for your home and save money. Here's a room-by-room roundup of inspiring, free (or almost free), eco-friendly DIY projects for your EcoNest. Click on the project for the tutorial. I've included two projects for each room!
Kitchen
1. Compost Holder-
An easy and green DIY project that uses a two gallon bucket, a scrubbing pad and some glue.
2. Reusable Swiffer Pad-
The creator of this project sums up why she came up with this cleaning solution. "I contemplated tossing the dreaded Swiffer, because every time I looked at it, I felt more and more guilty about my purchase. But since I already felt guilty about throwing all those pads away, why would I throw the Swiffer away? It was then that I decided to make my own re-useable Swiffer pads?"
Dining Room
3. Dining Table Made From A Door-
This dining table is stunning and has endless possibilities. The creator used an old wood door and four IKEA table legs. This table could easily be made with just these two items, but to further the aesthetics of the table, the pictured table is lined with decorative paper and covered with tempered glass.
4.Hanging Glass Rack-
This is an easy project made from coat hangers.
Living Room
5. Art from paint chips-
This picture is a pixilated painting. It's made by cutting paint chips (from a home improvement store) into two inch squares. The painting process is much like a paint-by-number mosaic. Green Genius!
6. Suitcase Table-
This is a quirky project that uses a few antique suitcases and table legs.
Bedroom
7. Pillows From Shirts-
Got some old plaid shirts? These cozy plaid pillows are easy to sew up.
8. Cardboard Furniture-
This is an adventurous project, and it obviously isn't the best piece of furniture for a damp space. But, it's an interesting concept, especially if you've got a huge refrigerator box hanging around.
Kid's Room
9. Piñata-
Every day's a party with a hanging piñata. Make one with your kids.
10. Photo Blocks-
I did this with a school class. Fun to make, fun to play with and a fun decorating idea.
Bathroom
11. Bathmat made from recycled towels-
Wow, I love this project and have already started making one. You will need to purchase gridded matting, like the kind used for rug making.
12. Bamboo Curtain Rod-
This is an elegant, yet rustic idea for a shower curtain rod. It uses a sized piece of bamboo for the rod and a dried seed pod as a finial. Natural and inspiring!
Office
13. Paint Can Organizer-
Easy and free. If you don't have empty paint cans, ask at your local home improvement store.
14. Fabric Covered Mousepad-
This is another clever, simple project, and would make a great gift as well.
Den
15. Magazine Holders-
Empty cereal boxes make this DIY project free.
16. IPod Holder-
Print out the pattern on cardstock and fold for a nest for your IPod.
Craftroom/Studio
17. Tic Tac Storage-
All those little candy containers have a great reuse for capturing beads and small objects. Start collecting!
18. Spool Knitting Loom-
I remember making lots of long knitted ropes on spool looms when I was a Girl Scout. This DIY loom is all grown up.
Laundry Room
19. Window Screen Hamper-
This project requires some materials, but the main ingredients are old window screens. Very, very cool.
20. Laundry Soap Recipe-
What more can be said for a project that saves money, your health and the planet!
21. Love/hate Martha? Either way, check out Martha Stewart?s Craft of the Day. This site provides a dearth of ideas for home décor that range from bright green to not so green, but always beautify photographed and with easy to understand directions. Also, The Crafts Dept. is a treasure trove of inspiring projects.
Sunday, August 29, 2010
How to Go Green: Laundry
Top Tips for Greening Your Laundry
Don't Rush: Don't wash what's not really dirty. None other than the United Nations itself reports that you can consume up to five times less energy by wearing your jeans at least three times, washing them in cold water, and skipping the dryer or the iron.
Skip the Phosphates: Despite the billions of dollars spent to convince you otherwise, most commercial detergents are the same and are bad for the environment. For example, phosphates (a common ingredient in laundry soap) can cause algal blooms that negatively effect ecosystems and marine life. Shop green or simply make your own.
A Laundry List of Tips: Wash your laundry in cold water, dry clothes on a clothesline, don't use an iron, try public laundromats for more efficient machines, and so on. Hey, we did say there's a wide range of very attainable green changes involved here, didn't we?
Did You Know?
90% of the energy used by a typical washing machine is used to heat the water; only 10% is used to power the motor
The average increase in energy efficiency for a washing machine between 1981 and 2003 is 88%
The amount of carbon dioxide emissions saved each year by line-drying your family's laundry is 700 pounds
Don't Rush: Don't wash what's not really dirty. None other than the United Nations itself reports that you can consume up to five times less energy by wearing your jeans at least three times, washing them in cold water, and skipping the dryer or the iron.
Skip the Phosphates: Despite the billions of dollars spent to convince you otherwise, most commercial detergents are the same and are bad for the environment. For example, phosphates (a common ingredient in laundry soap) can cause algal blooms that negatively effect ecosystems and marine life. Shop green or simply make your own.
A Laundry List of Tips: Wash your laundry in cold water, dry clothes on a clothesline, don't use an iron, try public laundromats for more efficient machines, and so on. Hey, we did say there's a wide range of very attainable green changes involved here, didn't we?
Did You Know?
90% of the energy used by a typical washing machine is used to heat the water; only 10% is used to power the motor
The average increase in energy efficiency for a washing machine between 1981 and 2003 is 88%
The amount of carbon dioxide emissions saved each year by line-drying your family's laundry is 700 pounds
Keep Cool This Summer Without Turning on the A/C
The summer heat is coming on fast, and it can be hard to resist turning to the air conditioning for relief, even for people with the greenest of lifestyles. But the A/C is one of the most energy-intensive appliances around and the more we can stay away from it, the better off our planet will be.
The Refresh Blog has some handy tips for keeping cool this summer without the A/C.
Check out how easy steps to fix your lighting can stop emitting so much heat into your home, or how insulating your pipes even with a simple blanket will help lower temperatures and also save you money.
Some of the tips are obvious, yet we still don't do them: skip the dryer and opt for a clothesline instead, unplug electronics when not in use—something that helps reduce energy consumption anyway, so that should a year-round habit—and do your best to avoid cooking in the oven. (You can use an outdoor grill, which at least keeps the heat outside, but better yet, try a solar cooker. They're easy to make yourself, and can even be a great reuse project for old CDs.)
Go for a white roof or other light color, or even better a green roof, and keep the curtains closed during the day to block out the most potent source of summer heat. Read the rest of the post to learn how to maximize your landscaping and choose the best fans for maximum ventilation—all to keep cool without ever turning on the A/C.
The Refresh Blog has some handy tips for keeping cool this summer without the A/C.
Check out how easy steps to fix your lighting can stop emitting so much heat into your home, or how insulating your pipes even with a simple blanket will help lower temperatures and also save you money.
Some of the tips are obvious, yet we still don't do them: skip the dryer and opt for a clothesline instead, unplug electronics when not in use—something that helps reduce energy consumption anyway, so that should a year-round habit—and do your best to avoid cooking in the oven. (You can use an outdoor grill, which at least keeps the heat outside, but better yet, try a solar cooker. They're easy to make yourself, and can even be a great reuse project for old CDs.)
Go for a white roof or other light color, or even better a green roof, and keep the curtains closed during the day to block out the most potent source of summer heat. Read the rest of the post to learn how to maximize your landscaping and choose the best fans for maximum ventilation—all to keep cool without ever turning on the A/C.
Tuesday, August 10, 2010
how earth was made
Look down beneath your feet. Have you ever wondered what you're really standing on? What is the Earth made of?If you could take the entire planet, sort it out into its various elements into piles, you'd have the following: 32% iron, 30% oxygen, 15% silicon, 14% magnesium, 3% sulfur, 2% nickel, and then much smaller piles of calcium, aluminum, and other trace elements.Obviously, we don't breath an iron atmosphere or swim in oceans of silicon. The elements of Earth are layered in the planet.We live on the outermost layer of Earth, called the crust. This varies in depth between 5 and 75 km. It's mostly made of silicates, with a tremendous amount of oxygen mixed in. In fact, 47% of the Earth's crust is oxygen. The thickest parts of the crust are under the continents, and the thinnest parts are underneath the oceans.Beneath this crust is the mantle, which goes down to a depth of 2890 km. It's the largest layer on Earth, and mostly consists of silicate rocks rich in iron and magnesium. Volcanoes are places where this mantle wells up through the crust.Below the mantle is the core, which is broken up into two parts: a solid inner core with a radius of 1,220 km, and then a liquid outer core that goes out to a radius of 3,400 km. Scientists think that the core consists mostly of iron (80%), which pulled together into the middle of the planet during the formation of the Earth, 4.5 billion years ago
Monday, July 19, 2010
The String is The Thing Brian Greene Unravels the Fabric of the Universe
The String is The Thing
Brian Greene Unravels the Fabric of the Universe
One doesn’t expect to see a theoretical physicist on the Late Show with David Letterman. But there sat Brian Greene, Columbia professor of mathematics and of physics, last March. His hair was graying around the temples, which accentuated a passing resemblance to Richard Gere, and he was at ease in front of the audience and the studio’s bright lights; his gestures were theatrical but precise. He was promoting his second book, The Fabric of the Cosmos: Space,Time, and the Texture of Reality. He was sincere when explaining his work in string theory, an ambitious attempt to unite the clashing domains of gravity and quantum physics. Letterman listened intently, and then asked,“So, how is my life better for this?” Greene responded earnestly that the theory has the potential to peer back before the Big Bang and explain how the universe began.“I think that would really alert us to our own place in the cosmos in a deep way.” “Does your head ache all the time?” Letterman asked.The scientist giggled. Greene was on television that night not merely to serve as Letterman’s foil, but to communicate his passion. He has gone to great lengths to make modern physics accessible to ordinary people and to help them understand how it alters our conventional notions of reality.When he talks about his chosen field, he sounds spiritual.“Science is a full-body experience,” Greene, 42, says.“It makes the heart beat fast when a result is working well. I’ve long since felt the public has a misconception about science: that it’s something that only makes use of the mind. But it really touches the soul when you reveal deep truths about the universe.” Television is one method Greene has used to spread those deep truths. His appearance on the Late Show was actually his second. His first was in fall 2003 when the PBS program NOVA aired The Elegant Universe, a documentary based on his first book of the same name.“He’s a wonderful writer, a wonderful talker,” says Paula Apsell, NOVA’s senior executive producer.“When he’s explaining something to you, it feels really clear.” The show won a Peabody Award for broadcast excellence.
It doesn’t hurt that string theory seems tailor made to capture the public imagination. The fundamental picture the theory presents is deceptively simple. If you could put a subatomic particle under an ultrapowerful microscope and magnify it billions and billions of times, you would find that it is actually a twodimensional vibrating filament, or string. “A violin string is not a bad picture to have in mind,” Greene says. Strings can vibrate in different ways, and each kind of vibration — every note, if you will — corresponds to a different particle.The theory presupposes that the infinitesimally small strings wriggle in and out of dimensions of space that we can’t see. Proponents say string theory could give physicists a single fundamental description of the universe from its inception.
Greene first spoke on string theory to the public in 1996 at a conference in Aspen, Colorado. Encouraged by his audience’s desire to learn more but unable to refer them to a popular book on the subject, he began work on his own.Three years later The Elegant Universe was complete.“I was very impressed by it,” says Greene’s colleague and friend, David Morrison of Duke University. “It was really quite remarkable in its ability to convey rather abstract physical concepts to lay audiences.” Those lay audiences apparently agreed. “The first weekend The Elegant Universe was in stores, it completely sold out,” Greene recalls. “And it went to number one on Amazon for three days.” The book became a national best seller, selling more than one million copies, and was a finalist for the Pulitzer Prize. Prospective physics majors at Oxford regularly rank The Elegant Universe second to Stephen Hawking’s A Brief History of Time as the book that most influenced them, says Graham Ross, a theoretical physicist at Oxford, who advised Greene as a Rhodes Scholar. Leonard Susskind of Stanford University, one of the originators of string theory, says Greene “has a marvelous ability to use metaphor and analogy to illustrate difficult physical ideas.” Greene went on tour and did a circuit of late-night shows — Nightline, The Charlie Rose Show, and Late Night with Conan O’Brien. “It became hard to get him on the phone,” says Morrison. Greene downplays his celebrity.“I really view physics as the celebrity that people have newly discovered,” he says. “I take pleasure in helping people understand the world around them a little bit more deeply.The greatest gratification I have is when a six-, seven-, or eight-year-old writes to me, and they’ve seen the program, and they’re so excited, and they want to maybe go into science and physics.”
Untangling The Universe
String theory weds general relativity, Einstein’s theory of gravity, with quantum physics. Einstein’s theory describes the universe’s shape as a whole. It says the universe is made of a smooth and continuous fabric-like entity called “spacetime.” In The Fabric of the Cosmos, Greene describes spacetime as a loaf of bread; its length represents time’s passing and its height and width represent space’s extent. In effect, observers moving at different speeds “slice” the same loaf of bread at different angles, carving out different amounts of duration and extent — and thus disagree about the passage of time and the dimensions of objects. General relativity says that the loaf is rubbery. Massive objects such as the sun warp and curve spacetime as a bowling ball would bend a trampoline. Less massive objects follow these warpings; thus the orbit of the planets, the bending of light by the sun, and the falling of apples. “It’s as if matter and energy imprint a network of chutes and valleys along which objects are guided by the invisible hand of the spacetime fabric,” Greene writes in Fabric. But Einstein’s theory breaks down when matter is packed together cheek by jowl and gravity becomes extremely strong, such as inside black holes or before the Big Bang, which kicked off our universe.
Quantum physics, on the other hand, describes particles of matter. In The Elegant Universe, Greene illustrates the theory by imagining two space travelers who stop at a mysterious bar for drinks. When the drinks arrive, they observe to their astonishment that the ice cubes in the glasses are rattling around of their own accord, like energetic bumper cars. In the smaller of the two glasses, the ice rattles faster, and one of the ice cubes bizarrely teleports through the side of the glass and falls to the floor. The story is designed to demonstrate Werner Heisenberg’s “uncertainty principle,” which dictates that small particles have no definite position in space, and the smaller the region confining them, the more indefinite their position. But mathematically and conceptually, quantum physics butts heads with general relativity.When physicists try to apply the uncertainty principle to general relativity, spacetime becomes infinitely jittery, which makes no sense.
String theory, if proved right, brings quantum physics and general relativity together. Strings inherently obey quantum physics.Their vibrations, the ones that give rise to different particles, are like the rattlings of the ice cubes in the quantum bar. These vibrations can accommodate a huge number of particles, including all the known particles and the graviton, a hypothetical particle that transmits the tug of gravity. So all of the forces are present, all come from the same stuff, and all obey the laws of quantum physics.
Origins of Physicist
Greene’s upbringing offers a hint of his trajectory. He grew up in Manhattan, and his family was enterprising and creative if not academic. His mother managed a veterinarian’s office and his father was a composer and had a minor hit in the 1960s with “Turn Around,” recorded by Harry Belafonte. Alan Greene never finished high school, but he had a great fondness for science and math and taught his son to multiply at a young age. By four or five Greene was solving enormous multiplication problems involving up to 30-digit numbers, written out by his father on construction paper.
When he was 12, in 1975, he had exhausted the high school mathematics curriculum, so his teacher at I.S. 44 on West 77th Street suggested he look for a math tutor at Columbia.With his 14-year-old sister along for moral support, he poked into offices in the computer science and math departments, handing uninterested researchers a note from his teacher requesting help for a precocious kid.The Greene siblings finally found a PhD candidate, Neil Bellinson, to tutor Greene in subjects such as advanced geometry and the theory of numbers, at no expense. “He didn’t have to teach me,” says Greene. “He didn’t get anything out of it beyond the joy of someone younger being initiated into this wondrous world.”
He first discovered and fell in love with physics at Stuyvesant High School in downtown Manhattan, famous for nurturing prodigies.“It became clear that the math I’d spent so much time thinking about and enjoying could actually be used to do something,” he says.“When that realization hit me, it was like a thunderbolt.” In 1980 he entered Harvard at age 17 and was drawn to Einstein’s theory of general relativity. He bought a textbook on the subject and carried it around campus.“It was beyond me, but I just wanted it near me,” he says. “I had this burning urge to learn Einstein’s theory.”
For decades physicists have been trying to unify gravity with the three other forces in the universe: electromagnetism and the strong and weak nuclear forces, which keep the nuclei of atoms together. Einstein struggled for 30 years to fuse general relativity and electromagnetism, to no avail. Gravity refuses to cooperate because the other forces all obey quantum rules. After graduating from Harvard, Greene went as a Rhodes Scholar to Oxford, where he got his first chance to work on the unification problem.
String theory, a weird idea that would combine the forces, had been floating around for about a decade. It had been plagued by mathematical inconsistencies until the year of Greene’s arrival at Oxford, when two pioneers finally showed that this esoteric scheme had a shot at describing the real world. Greene and his adviser, Graham Ross, set to work.“It was a grand opportunity to perhaps work on the theory that Einstein himself was looking for but never found,”Greene says.“That was a temptation none of us could, or even would, think about resisting.”
String theory requires space to have 9 or 10 dimensions — more than the 3 that we can easily observe.The 6 or 7 dimensions that we can’t observe are “curled up” and too small to see. If that seems difficult to imagine, think of the way that a clothes-line looks one-dimensional from far enough away. If you never got close enough to the line, you might never know it had thickness. Similarly, unless you were the size of the strings in string theory, you would never be able to wiggle around in these hypothetical extra dimensions. Physicists are willing to bother with such a strange idea because their current theories leave tantalizing gaps in our understanding of the universe. String theory is one of the most mathematically daunting fields in physics, but Greene’s facility with numbers helped him achieve a prominent place among its younger practitioners. He and two other students constructed a model describing how the extra dimensions of string theory might get curled up in such a way to produce known particle physics.“It failed in the details, but it was the first one of its time to get close,” says Ross. (All other string theory models have so far failed to match precisely the known particles, too — something critics of string theory point to.) The attempt brought Greene and his classmates recognition. “They’d sort of gone from scratch to world leaders,” Ross says.
At Oxford, Greene began taking intensive acting classes. “I really enjoyed having my mind go in a very different place than it generally is when I’m doing my own work,” he says. “I used to go to these three-hour acting classes and after I left, it’d be like, ‘Wow, I was just in a completely different universe than I ordinarily am,’ and I love that.”
Theater was common at Oxford, but his other qualities set Greene apart even from the highly talented crowd at the school, says Ross. “It was clear that Brian was unusual,” he recalls.“He was very, very smart and he had an ability to communicate. He was always a very charismatic character.”
After Oxford, Greene, then 23, returned to Harvard as a postdoctoral fellow. There he began making his biggest scientific contributions so far. As he thought about the extra dimensions of string theory, he found himself convinced of a surprising conjecture by other theorists. In general relativity, every spacetime geometry, or shape, is unique. Each one corresponds to a different network of the “chutes and valleys.” In 1990, shortly before he took a position at Cornell University, Greene helped prove that string theory’s extra dimensions could be curled up in two geometrically distinct ways but still yield the same physics.The relationship between the two distinct but equivalent shapes is called “mirror symmetry” (although the pairs of extra dimensions are not literally mirror images of each other).“Mirror symmetry remains a deep mathematical mystery,” says John Morgan, chair of Columbia’s mathematics department.The beauty of the symmetry is that it sometimes allows very difficult calculations to be recast in an easier form by switching to an equivalent version of a problem. In an example of such a switch, Greene and two colleagues, Paul Aspinwall and David Morrison, both of Duke, discovered that the extra dimensions of string theory could rip and reseal without causing catastrophic problems for the theory. Part of the extra dimensions of space can become pinched off as if it were a ball of dough or clay being pulled in different directions. It starts looking like a dumbbell and then rips in the middle. But just after it rips, a new sphere grows from the ripped spot and seals it.There is no rip in the mirror description, and the process is consistent with known physics.
Impressed, Columbia’s mathematics department lured Greene from Cornell in 1996, right before his second career as popular science expositor took off. At first he had no desire to return home to New York City. “It just didn’t strike me as a quiet enough place to sit and think,” he says. But he was dating an aspiring actress who wanted to move there. Although he and the actress split up, he has since married Tracy Day, a television producer he met doing a segment for ABC News. Their son, Alec, was born early last year. Manhattan also offers numerous opportunities for Greene to indulge his taste for what he calls “nontraditional” approaches to education. Consider “Strings and Strings,” his collaboration with the Emerson String Quartet, which was performed in 2000 as part of the Works and Process series at the Guggenheim Museum. Greene and the quartet took turns in a seamless physics-music dialogue: Greene would speak briefly about string theory, segueing into metaphorical language that the quartet would then expand upon by playing a few minutes of music designed to capture an aspect of the science. The Canadian director Robert Lepage is working with Greene to expand “Strings and Strings” into a “theatrical piece with a narrative backbone that will intertwine physics and music, with the core being the way they interface with time,” says Greene. Tentatively scheduled for Lincoln Center’s 2008 season, it will be part of a massive science-forthe- public gathering now being developed by the Science Festival Foundation — a nonprofit company founded by Greene and his wife. The festival will bring together cuttingedge scientists from around the world for a week of panel discussions, lectures, and debates at a number of universities, including Columbia, throughout the city. Cultural institutions will hold music, dance, and other types of performances, with all of the works emphasizing a scientific connection. Greene still finds time for work, too.
His interests have swung back and forth between the more mathematical side of string theory, such as the work that led him to mirror symmetry, and research more grounded in observation and known physics. He cofounded the University’s Institute for Strings, Cosmology, and Astroparticle Physics (ISCAP) in 2000, reflecting his current interests in applying string theory to the origin of the universe and finding consequences of the theory that could be observed with telescopes. Lately, he has been studying whether strings could have left an impression on the microwave radiation that fills the universe. The universe expanded rapidly in its early moments, which might have blown up the signatures of strings — like writing on a balloon as it’s being inflated — resulting in tiny temperature variations across the cosmos that might be detectable.While Greene views this possibility as a long shot, a successful outcome would provide the first experimental support for string theory. Greene draws on other ways of thinking as well.
He dabbled in Buddhism as an undergraduate. In the introduction to Fabric, he tells of the lasting impression left on him by the existentialist philosopher Albert Camus’s book The Myth of Sisyphus, which he pulled down from his father’s bookcase as a teenager. “I think it’s exciting,” he says, “that so many of us, in so many different ways, seek the true nature of reality.”
Whither String Theory?
String theorists have to be persevering. Despite making great progress in understanding the theory, they have yet to devise an ironclad way of testing it.The trouble stems from string theory’s extra dimensions, which can twist themselves together into a huge variety of shapes, each of which results in particles having slightly different masses, charges, and other properties. Nothing in the theory tells physicists which shape to choose. Even some string theorists have begun to abandon the idea of selecting one shape for the extra dimensions, arguing that the different dimensional contortions are equally realized in a larger “multiverse.”
Critics such as Peter Woit, a physicist in Columbia’s mathematics department, dwell on this point, complaining that the theory has virtually monopolized particle physics for two decades, with nothing to show. “The models they are working with just aren’t connected to the real world,” said Woit in a recent interview in Discover magazine.“There’s an ongoing discussion now almost at the level of philosophy of science: Is this even a science?”
Both camps have given up too early for Greene’s taste.The lack of a unique prediction may be a result of physicists’ poor understanding of the theory, he says. Quantum mechanics, which deals with molecules and atoms, took 30 years to formulate. “What we’re trying to do now is extend the reach of theory to things 100 billion billion times smaller” — and potentially that much further removed from experimental contact.“We’re on our own searching in mathematical realms for physical truth.”
Brian Greene Unravels the Fabric of the Universe
One doesn’t expect to see a theoretical physicist on the Late Show with David Letterman. But there sat Brian Greene, Columbia professor of mathematics and of physics, last March. His hair was graying around the temples, which accentuated a passing resemblance to Richard Gere, and he was at ease in front of the audience and the studio’s bright lights; his gestures were theatrical but precise. He was promoting his second book, The Fabric of the Cosmos: Space,Time, and the Texture of Reality. He was sincere when explaining his work in string theory, an ambitious attempt to unite the clashing domains of gravity and quantum physics. Letterman listened intently, and then asked,“So, how is my life better for this?” Greene responded earnestly that the theory has the potential to peer back before the Big Bang and explain how the universe began.“I think that would really alert us to our own place in the cosmos in a deep way.” “Does your head ache all the time?” Letterman asked.The scientist giggled. Greene was on television that night not merely to serve as Letterman’s foil, but to communicate his passion. He has gone to great lengths to make modern physics accessible to ordinary people and to help them understand how it alters our conventional notions of reality.When he talks about his chosen field, he sounds spiritual.“Science is a full-body experience,” Greene, 42, says.“It makes the heart beat fast when a result is working well. I’ve long since felt the public has a misconception about science: that it’s something that only makes use of the mind. But it really touches the soul when you reveal deep truths about the universe.” Television is one method Greene has used to spread those deep truths. His appearance on the Late Show was actually his second. His first was in fall 2003 when the PBS program NOVA aired The Elegant Universe, a documentary based on his first book of the same name.“He’s a wonderful writer, a wonderful talker,” says Paula Apsell, NOVA’s senior executive producer.“When he’s explaining something to you, it feels really clear.” The show won a Peabody Award for broadcast excellence.
It doesn’t hurt that string theory seems tailor made to capture the public imagination. The fundamental picture the theory presents is deceptively simple. If you could put a subatomic particle under an ultrapowerful microscope and magnify it billions and billions of times, you would find that it is actually a twodimensional vibrating filament, or string. “A violin string is not a bad picture to have in mind,” Greene says. Strings can vibrate in different ways, and each kind of vibration — every note, if you will — corresponds to a different particle.The theory presupposes that the infinitesimally small strings wriggle in and out of dimensions of space that we can’t see. Proponents say string theory could give physicists a single fundamental description of the universe from its inception.
Greene first spoke on string theory to the public in 1996 at a conference in Aspen, Colorado. Encouraged by his audience’s desire to learn more but unable to refer them to a popular book on the subject, he began work on his own.Three years later The Elegant Universe was complete.“I was very impressed by it,” says Greene’s colleague and friend, David Morrison of Duke University. “It was really quite remarkable in its ability to convey rather abstract physical concepts to lay audiences.” Those lay audiences apparently agreed. “The first weekend The Elegant Universe was in stores, it completely sold out,” Greene recalls. “And it went to number one on Amazon for three days.” The book became a national best seller, selling more than one million copies, and was a finalist for the Pulitzer Prize. Prospective physics majors at Oxford regularly rank The Elegant Universe second to Stephen Hawking’s A Brief History of Time as the book that most influenced them, says Graham Ross, a theoretical physicist at Oxford, who advised Greene as a Rhodes Scholar. Leonard Susskind of Stanford University, one of the originators of string theory, says Greene “has a marvelous ability to use metaphor and analogy to illustrate difficult physical ideas.” Greene went on tour and did a circuit of late-night shows — Nightline, The Charlie Rose Show, and Late Night with Conan O’Brien. “It became hard to get him on the phone,” says Morrison. Greene downplays his celebrity.“I really view physics as the celebrity that people have newly discovered,” he says. “I take pleasure in helping people understand the world around them a little bit more deeply.The greatest gratification I have is when a six-, seven-, or eight-year-old writes to me, and they’ve seen the program, and they’re so excited, and they want to maybe go into science and physics.”
Untangling The Universe
String theory weds general relativity, Einstein’s theory of gravity, with quantum physics. Einstein’s theory describes the universe’s shape as a whole. It says the universe is made of a smooth and continuous fabric-like entity called “spacetime.” In The Fabric of the Cosmos, Greene describes spacetime as a loaf of bread; its length represents time’s passing and its height and width represent space’s extent. In effect, observers moving at different speeds “slice” the same loaf of bread at different angles, carving out different amounts of duration and extent — and thus disagree about the passage of time and the dimensions of objects. General relativity says that the loaf is rubbery. Massive objects such as the sun warp and curve spacetime as a bowling ball would bend a trampoline. Less massive objects follow these warpings; thus the orbit of the planets, the bending of light by the sun, and the falling of apples. “It’s as if matter and energy imprint a network of chutes and valleys along which objects are guided by the invisible hand of the spacetime fabric,” Greene writes in Fabric. But Einstein’s theory breaks down when matter is packed together cheek by jowl and gravity becomes extremely strong, such as inside black holes or before the Big Bang, which kicked off our universe.
Quantum physics, on the other hand, describes particles of matter. In The Elegant Universe, Greene illustrates the theory by imagining two space travelers who stop at a mysterious bar for drinks. When the drinks arrive, they observe to their astonishment that the ice cubes in the glasses are rattling around of their own accord, like energetic bumper cars. In the smaller of the two glasses, the ice rattles faster, and one of the ice cubes bizarrely teleports through the side of the glass and falls to the floor. The story is designed to demonstrate Werner Heisenberg’s “uncertainty principle,” which dictates that small particles have no definite position in space, and the smaller the region confining them, the more indefinite their position. But mathematically and conceptually, quantum physics butts heads with general relativity.When physicists try to apply the uncertainty principle to general relativity, spacetime becomes infinitely jittery, which makes no sense.
String theory, if proved right, brings quantum physics and general relativity together. Strings inherently obey quantum physics.Their vibrations, the ones that give rise to different particles, are like the rattlings of the ice cubes in the quantum bar. These vibrations can accommodate a huge number of particles, including all the known particles and the graviton, a hypothetical particle that transmits the tug of gravity. So all of the forces are present, all come from the same stuff, and all obey the laws of quantum physics.
Origins of Physicist
Greene’s upbringing offers a hint of his trajectory. He grew up in Manhattan, and his family was enterprising and creative if not academic. His mother managed a veterinarian’s office and his father was a composer and had a minor hit in the 1960s with “Turn Around,” recorded by Harry Belafonte. Alan Greene never finished high school, but he had a great fondness for science and math and taught his son to multiply at a young age. By four or five Greene was solving enormous multiplication problems involving up to 30-digit numbers, written out by his father on construction paper.
When he was 12, in 1975, he had exhausted the high school mathematics curriculum, so his teacher at I.S. 44 on West 77th Street suggested he look for a math tutor at Columbia.With his 14-year-old sister along for moral support, he poked into offices in the computer science and math departments, handing uninterested researchers a note from his teacher requesting help for a precocious kid.The Greene siblings finally found a PhD candidate, Neil Bellinson, to tutor Greene in subjects such as advanced geometry and the theory of numbers, at no expense. “He didn’t have to teach me,” says Greene. “He didn’t get anything out of it beyond the joy of someone younger being initiated into this wondrous world.”
He first discovered and fell in love with physics at Stuyvesant High School in downtown Manhattan, famous for nurturing prodigies.“It became clear that the math I’d spent so much time thinking about and enjoying could actually be used to do something,” he says.“When that realization hit me, it was like a thunderbolt.” In 1980 he entered Harvard at age 17 and was drawn to Einstein’s theory of general relativity. He bought a textbook on the subject and carried it around campus.“It was beyond me, but I just wanted it near me,” he says. “I had this burning urge to learn Einstein’s theory.”
For decades physicists have been trying to unify gravity with the three other forces in the universe: electromagnetism and the strong and weak nuclear forces, which keep the nuclei of atoms together. Einstein struggled for 30 years to fuse general relativity and electromagnetism, to no avail. Gravity refuses to cooperate because the other forces all obey quantum rules. After graduating from Harvard, Greene went as a Rhodes Scholar to Oxford, where he got his first chance to work on the unification problem.
String theory, a weird idea that would combine the forces, had been floating around for about a decade. It had been plagued by mathematical inconsistencies until the year of Greene’s arrival at Oxford, when two pioneers finally showed that this esoteric scheme had a shot at describing the real world. Greene and his adviser, Graham Ross, set to work.“It was a grand opportunity to perhaps work on the theory that Einstein himself was looking for but never found,”Greene says.“That was a temptation none of us could, or even would, think about resisting.”
String theory requires space to have 9 or 10 dimensions — more than the 3 that we can easily observe.The 6 or 7 dimensions that we can’t observe are “curled up” and too small to see. If that seems difficult to imagine, think of the way that a clothes-line looks one-dimensional from far enough away. If you never got close enough to the line, you might never know it had thickness. Similarly, unless you were the size of the strings in string theory, you would never be able to wiggle around in these hypothetical extra dimensions. Physicists are willing to bother with such a strange idea because their current theories leave tantalizing gaps in our understanding of the universe. String theory is one of the most mathematically daunting fields in physics, but Greene’s facility with numbers helped him achieve a prominent place among its younger practitioners. He and two other students constructed a model describing how the extra dimensions of string theory might get curled up in such a way to produce known particle physics.“It failed in the details, but it was the first one of its time to get close,” says Ross. (All other string theory models have so far failed to match precisely the known particles, too — something critics of string theory point to.) The attempt brought Greene and his classmates recognition. “They’d sort of gone from scratch to world leaders,” Ross says.
At Oxford, Greene began taking intensive acting classes. “I really enjoyed having my mind go in a very different place than it generally is when I’m doing my own work,” he says. “I used to go to these three-hour acting classes and after I left, it’d be like, ‘Wow, I was just in a completely different universe than I ordinarily am,’ and I love that.”
Theater was common at Oxford, but his other qualities set Greene apart even from the highly talented crowd at the school, says Ross. “It was clear that Brian was unusual,” he recalls.“He was very, very smart and he had an ability to communicate. He was always a very charismatic character.”
After Oxford, Greene, then 23, returned to Harvard as a postdoctoral fellow. There he began making his biggest scientific contributions so far. As he thought about the extra dimensions of string theory, he found himself convinced of a surprising conjecture by other theorists. In general relativity, every spacetime geometry, or shape, is unique. Each one corresponds to a different network of the “chutes and valleys.” In 1990, shortly before he took a position at Cornell University, Greene helped prove that string theory’s extra dimensions could be curled up in two geometrically distinct ways but still yield the same physics.The relationship between the two distinct but equivalent shapes is called “mirror symmetry” (although the pairs of extra dimensions are not literally mirror images of each other).“Mirror symmetry remains a deep mathematical mystery,” says John Morgan, chair of Columbia’s mathematics department.The beauty of the symmetry is that it sometimes allows very difficult calculations to be recast in an easier form by switching to an equivalent version of a problem. In an example of such a switch, Greene and two colleagues, Paul Aspinwall and David Morrison, both of Duke, discovered that the extra dimensions of string theory could rip and reseal without causing catastrophic problems for the theory. Part of the extra dimensions of space can become pinched off as if it were a ball of dough or clay being pulled in different directions. It starts looking like a dumbbell and then rips in the middle. But just after it rips, a new sphere grows from the ripped spot and seals it.There is no rip in the mirror description, and the process is consistent with known physics.
Impressed, Columbia’s mathematics department lured Greene from Cornell in 1996, right before his second career as popular science expositor took off. At first he had no desire to return home to New York City. “It just didn’t strike me as a quiet enough place to sit and think,” he says. But he was dating an aspiring actress who wanted to move there. Although he and the actress split up, he has since married Tracy Day, a television producer he met doing a segment for ABC News. Their son, Alec, was born early last year. Manhattan also offers numerous opportunities for Greene to indulge his taste for what he calls “nontraditional” approaches to education. Consider “Strings and Strings,” his collaboration with the Emerson String Quartet, which was performed in 2000 as part of the Works and Process series at the Guggenheim Museum. Greene and the quartet took turns in a seamless physics-music dialogue: Greene would speak briefly about string theory, segueing into metaphorical language that the quartet would then expand upon by playing a few minutes of music designed to capture an aspect of the science. The Canadian director Robert Lepage is working with Greene to expand “Strings and Strings” into a “theatrical piece with a narrative backbone that will intertwine physics and music, with the core being the way they interface with time,” says Greene. Tentatively scheduled for Lincoln Center’s 2008 season, it will be part of a massive science-forthe- public gathering now being developed by the Science Festival Foundation — a nonprofit company founded by Greene and his wife. The festival will bring together cuttingedge scientists from around the world for a week of panel discussions, lectures, and debates at a number of universities, including Columbia, throughout the city. Cultural institutions will hold music, dance, and other types of performances, with all of the works emphasizing a scientific connection. Greene still finds time for work, too.
His interests have swung back and forth between the more mathematical side of string theory, such as the work that led him to mirror symmetry, and research more grounded in observation and known physics. He cofounded the University’s Institute for Strings, Cosmology, and Astroparticle Physics (ISCAP) in 2000, reflecting his current interests in applying string theory to the origin of the universe and finding consequences of the theory that could be observed with telescopes. Lately, he has been studying whether strings could have left an impression on the microwave radiation that fills the universe. The universe expanded rapidly in its early moments, which might have blown up the signatures of strings — like writing on a balloon as it’s being inflated — resulting in tiny temperature variations across the cosmos that might be detectable.While Greene views this possibility as a long shot, a successful outcome would provide the first experimental support for string theory. Greene draws on other ways of thinking as well.
He dabbled in Buddhism as an undergraduate. In the introduction to Fabric, he tells of the lasting impression left on him by the existentialist philosopher Albert Camus’s book The Myth of Sisyphus, which he pulled down from his father’s bookcase as a teenager. “I think it’s exciting,” he says, “that so many of us, in so many different ways, seek the true nature of reality.”
Whither String Theory?
String theorists have to be persevering. Despite making great progress in understanding the theory, they have yet to devise an ironclad way of testing it.The trouble stems from string theory’s extra dimensions, which can twist themselves together into a huge variety of shapes, each of which results in particles having slightly different masses, charges, and other properties. Nothing in the theory tells physicists which shape to choose. Even some string theorists have begun to abandon the idea of selecting one shape for the extra dimensions, arguing that the different dimensional contortions are equally realized in a larger “multiverse.”
Critics such as Peter Woit, a physicist in Columbia’s mathematics department, dwell on this point, complaining that the theory has virtually monopolized particle physics for two decades, with nothing to show. “The models they are working with just aren’t connected to the real world,” said Woit in a recent interview in Discover magazine.“There’s an ongoing discussion now almost at the level of philosophy of science: Is this even a science?”
Both camps have given up too early for Greene’s taste.The lack of a unique prediction may be a result of physicists’ poor understanding of the theory, he says. Quantum mechanics, which deals with molecules and atoms, took 30 years to formulate. “What we’re trying to do now is extend the reach of theory to things 100 billion billion times smaller” — and potentially that much further removed from experimental contact.“We’re on our own searching in mathematical realms for physical truth.”
Friday, April 16, 2010
How Rocket Engines Work
One of the most amazing endeavors man has ever undertaken is the exploration of space. A big p art of the amazement is the complexity. Space exploration is complicated because there are so many problems to solve and obstacles to overcome. You have things like:
The vacuum of space
Heat management problems
The difficulty of re-entry
Orbital mechanics
Micrometeorites and space debris
Cosmic and solar radiation
The logistics of having restroom facilities in a weightless environment
But the biggest problem of all is harnessing enough energy simply to get a spaceship off the ground. That is where rocket engines come in.
Rocket engines are, on the one hand, so simple that you can build and fly your own model rockets very inexpensively (see the links on the last page of the article for details). On the other hand, rocket engines (and their fuel systems) are so complicated that only three countries have actually ever put people in orbit. In this article, we will look at rocket engines to understand how they work, as well as to understand some of the complexity surrounding them.
Wh en most people think about motors or engines, they think about rotation. For example, a reciprocating gasoline engine in a car produces rotational energy to drive the wheels. An electric motor produces rotational energy to drive a fan or spin a disk. A steam engine is used to do the same thing, as is a steam turbine and most gas turbines.
Rocket engines are fundamentally different. Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction." A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result.
This concept of "throwing mass and benefiting from the reaction" can be hard to grasp at first, because that does not seem to be what is happening. Rocket engines seem to be about flames and noise and pressure, not "throwing things." Let's look at a few examples to get a better picture of reality:
If you have ever shot a shotgun, especially a big 12-gauge shotgun, then you know that it has a lot of "kick." That is, when you shoot the gun it "kicks" your shoulder back with a great deal of force. That kick is a reaction. A shotgun is shooting about an ounce of metal in one direction at about 700 miles per hour, and your shoulder gets hit with the reaction. If you were wearing roller skates or standing on a skateboard when you shot the gun, then the gun would be acting like a rocket engine and you would react by rolling in the opposite direction.
If you have ever seen a big fire hose spraying water, you may have noticed that it takes a lot of strength to hold the hose (sometimes you will see two or three firefighters holding the hose). The hose is acting like a rocket engine. The hose is throwing water in one direction, and the firefighters are using their strength and weight to counteract the reaction. If they were to let go of the hose, it would thrash around with tremendous force. If the firefighters were all standing on skateboards, the hose would propel them backward at great speed!
When you blow up a balloon and let it go so that it flies all over the room before running out of air, you have created a rocket engine. In this case, what is being thrown is the air molecules inside the balloon. Many people believe that air molecules don't weigh anything, but they do (see the page on helium to get a better picture of the weight of air). When you throw them out the nozzle of a balloon, the rest of the balloon reacts in the opposite direction.
Action and Reaction: The Space Baseball Scenario
Imagine the following situation: You are wearing a space suit and you are floating in space beside the space shuttle; you happen to have a baseball in your hand.
If you throw the baseball, your body will react by moving in the opposite direction of the ball. The thing that controls the speed at which your body moves away is the weight of the baseball that you throw and the amount of acceleration that you apply to it. Mass multiplied by acceleration is force (f = m * a). Whatever force you apply to the baseball will be equalized by an identical reaction force applied to your body (m * a = m * a). So let's say that the baseball weighs 1 pound, and your body plus the space suit weighs 100 pounds. You throw the baseball away at a speed of 32 feet per second (21 mph). That is to say, you accelerate the 1-pound baseball with your arm so that it obtains a velocity of 21 mph. Your body reacts, but it weighs 100 times more than the baseball. Therefore, it moves away at one-hundredth the velocity of the baseball, or 0.32 feet per second (0.21 mph).
If you want to generate more thrust from your baseball, you have two options: increase the mass or increase the acceleration. You can throw a heavier baseball or throw a number of baseballs one after another (increasing the mass), or you can throw the baseball faster (increasing the acceleration on it). But that is all that you can do.
A rocket engine is generally throwing mass in the form of a high-pressure gas. The engine throws the mass of gas out in one direction in order to get a reaction in the opposite direction. The mass comes from the weight of the fuel that the rocket engine burns. The burning process accelerates the mass of fuel so that it comes out of the rocket nozzle at high speed. The fact that the fuel turns from a solid or liquid into a gas when it burns does not change its mass. If you burn a pound of rocket fuel, a pound of exhaust comes out the nozzle in the form of a high-temperature, high-velocity gas. The form changes, but the mass does not. The burning process accelerates the mass.
Thrust
The "strength" of a rocket engine is called its thrust. Thrust is measured in "pounds of thrust" in the U.S. and in Newtons under the metric system (4.45 Newtons of thrust equals 1 pound of thrust). A pound of thrust is the amount of thrust it would take to keep a 1-pound object stationary against the force of gravity on Earth. So on Earth, the acceleration of gravity is 32 feet per second per second (21 mph per second). If you were floating in space with a bag of baseballs and you threw one baseball per second away from you at 21 mph, your baseballs would be generating the equivalent of 1 pound of thrust. If you were to throw the baseballs instead at 42 mph, then you would be generating 2 pounds of thrust. If you throw them at 2,100 mph (perhaps by shooting them out of some sort of baseball gun), then you are generating 100 pounds of thrust, and so on.
One of the funny problems rockets have is that the objects that the engine wants to throw actually weigh something, and the rocket has to carry that weight around. So let's say that you want to generate 100 pounds of thrust for an hour by throwing one baseball every second at a speed of 2,100 mph. That means that you have to start with 3,600 1-pound baseballs (there are 3,600 seconds in an hour), or 3,600 pounds of baseballs. Since you only weigh 100 pounds in your spacesuit, you can see that the weight of your "fuel" dwarfs the weight of the payload (you). In fact, the fuel weights 36 times more than the payload. And that is very common. That is why you have to have a huge rocket to get a tiny person into space right now -- you have to carry a lot of fuel.
You can see the weight equation very clearly on the Space Shuttle. If you have ever seen the Space Shuttle launch, you know that there are three parts:
The Orbiter
The big external tank
The two solid rocket boosters (SRBs)
The Orbiter weighs 165,000 pounds empty. The external tank weighs 78,100 pounds empty. The two solid rocket boosters weigh 185,000 pounds empty each. But then you have to load in the fuel. Each SRB holds 1.1 million pounds of fuel. The external tank holds 143,000 gallons of liquid oxygen (1,359,000 pounds) and 383,000 gallons of liquid hydrogen (226,000 pounds). The whole vehicle -- shuttle, external tank, solid rocket booster casings and all the fuel -- has a total weight of 4.4 million pounds at launch. 4.4 million pounds to get 165,000 pounds in orbit is a pretty big difference! To be fair, the orbiter can also carry a 65,000-pound payload (up to 15 x 60 feet in size), but it is still a big difference. The fuel weighs almost 20 times more than the Orbiter [source: The Space Shuttle Operator's Manual].
All of that fuel is being thrown out the back of the Space Shuttle at a speed of perhaps 6,000 mph (typical rocket exhaust velocities for chemical rockets range between 5,000 and 10,000 mph). The SRBs burn for about two minutes and generate about 3.3 million pounds of thrust each at launch (2.65 million pounds average over the burn). The three main engines (which use the fuel in the external tank) burn for about eight minutes, generating 375,000 pounds of thrust each during the burn.
The vacuum of space
Heat management problems
The difficulty of re-entry
Orbital mechanics
Micrometeorites and space debris
Cosmic and solar radiation
The logistics of having restroom facilities in a weightless environment
But the biggest problem of all is harnessing enough energy simply to get a spaceship off the ground. That is where rocket engines come in.
Rocket engines are, on the one hand, so simple that you can build and fly your own model rockets very inexpensively (see the links on the last page of the article for details). On the other hand, rocket engines (and their fuel systems) are so complicated that only three countries have actually ever put people in orbit. In this article, we will look at rocket engines to understand how they work, as well as to understand some of the complexity surrounding them.
Wh en most people think about motors or engines, they think about rotation. For example, a reciprocating gasoline engine in a car produces rotational energy to drive the wheels. An electric motor produces rotational energy to drive a fan or spin a disk. A steam engine is used to do the same thing, as is a steam turbine and most gas turbines.
Rocket engines are fundamentally different. Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction." A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result.
This concept of "throwing mass and benefiting from the reaction" can be hard to grasp at first, because that does not seem to be what is happening. Rocket engines seem to be about flames and noise and pressure, not "throwing things." Let's look at a few examples to get a better picture of reality:
If you have ever shot a shotgun, especially a big 12-gauge shotgun, then you know that it has a lot of "kick." That is, when you shoot the gun it "kicks" your shoulder back with a great deal of force. That kick is a reaction. A shotgun is shooting about an ounce of metal in one direction at about 700 miles per hour, and your shoulder gets hit with the reaction. If you were wearing roller skates or standing on a skateboard when you shot the gun, then the gun would be acting like a rocket engine and you would react by rolling in the opposite direction.
If you have ever seen a big fire hose spraying water, you may have noticed that it takes a lot of strength to hold the hose (sometimes you will see two or three firefighters holding the hose). The hose is acting like a rocket engine. The hose is throwing water in one direction, and the firefighters are using their strength and weight to counteract the reaction. If they were to let go of the hose, it would thrash around with tremendous force. If the firefighters were all standing on skateboards, the hose would propel them backward at great speed!
When you blow up a balloon and let it go so that it flies all over the room before running out of air, you have created a rocket engine. In this case, what is being thrown is the air molecules inside the balloon. Many people believe that air molecules don't weigh anything, but they do (see the page on helium to get a better picture of the weight of air). When you throw them out the nozzle of a balloon, the rest of the balloon reacts in the opposite direction.
Action and Reaction: The Space Baseball Scenario
Imagine the following situation: You are wearing a space suit and you are floating in space beside the space shuttle; you happen to have a baseball in your hand.
If you throw the baseball, your body will react by moving in the opposite direction of the ball. The thing that controls the speed at which your body moves away is the weight of the baseball that you throw and the amount of acceleration that you apply to it. Mass multiplied by acceleration is force (f = m * a). Whatever force you apply to the baseball will be equalized by an identical reaction force applied to your body (m * a = m * a). So let's say that the baseball weighs 1 pound, and your body plus the space suit weighs 100 pounds. You throw the baseball away at a speed of 32 feet per second (21 mph). That is to say, you accelerate the 1-pound baseball with your arm so that it obtains a velocity of 21 mph. Your body reacts, but it weighs 100 times more than the baseball. Therefore, it moves away at one-hundredth the velocity of the baseball, or 0.32 feet per second (0.21 mph).
If you want to generate more thrust from your baseball, you have two options: increase the mass or increase the acceleration. You can throw a heavier baseball or throw a number of baseballs one after another (increasing the mass), or you can throw the baseball faster (increasing the acceleration on it). But that is all that you can do.
A rocket engine is generally throwing mass in the form of a high-pressure gas. The engine throws the mass of gas out in one direction in order to get a reaction in the opposite direction. The mass comes from the weight of the fuel that the rocket engine burns. The burning process accelerates the mass of fuel so that it comes out of the rocket nozzle at high speed. The fact that the fuel turns from a solid or liquid into a gas when it burns does not change its mass. If you burn a pound of rocket fuel, a pound of exhaust comes out the nozzle in the form of a high-temperature, high-velocity gas. The form changes, but the mass does not. The burning process accelerates the mass.
Thrust
The "strength" of a rocket engine is called its thrust. Thrust is measured in "pounds of thrust" in the U.S. and in Newtons under the metric system (4.45 Newtons of thrust equals 1 pound of thrust). A pound of thrust is the amount of thrust it would take to keep a 1-pound object stationary against the force of gravity on Earth. So on Earth, the acceleration of gravity is 32 feet per second per second (21 mph per second). If you were floating in space with a bag of baseballs and you threw one baseball per second away from you at 21 mph, your baseballs would be generating the equivalent of 1 pound of thrust. If you were to throw the baseballs instead at 42 mph, then you would be generating 2 pounds of thrust. If you throw them at 2,100 mph (perhaps by shooting them out of some sort of baseball gun), then you are generating 100 pounds of thrust, and so on.
One of the funny problems rockets have is that the objects that the engine wants to throw actually weigh something, and the rocket has to carry that weight around. So let's say that you want to generate 100 pounds of thrust for an hour by throwing one baseball every second at a speed of 2,100 mph. That means that you have to start with 3,600 1-pound baseballs (there are 3,600 seconds in an hour), or 3,600 pounds of baseballs. Since you only weigh 100 pounds in your spacesuit, you can see that the weight of your "fuel" dwarfs the weight of the payload (you). In fact, the fuel weights 36 times more than the payload. And that is very common. That is why you have to have a huge rocket to get a tiny person into space right now -- you have to carry a lot of fuel.
You can see the weight equation very clearly on the Space Shuttle. If you have ever seen the Space Shuttle launch, you know that there are three parts:
The Orbiter
The big external tank
The two solid rocket boosters (SRBs)
The Orbiter weighs 165,000 pounds empty. The external tank weighs 78,100 pounds empty. The two solid rocket boosters weigh 185,000 pounds empty each. But then you have to load in the fuel. Each SRB holds 1.1 million pounds of fuel. The external tank holds 143,000 gallons of liquid oxygen (1,359,000 pounds) and 383,000 gallons of liquid hydrogen (226,000 pounds). The whole vehicle -- shuttle, external tank, solid rocket booster casings and all the fuel -- has a total weight of 4.4 million pounds at launch. 4.4 million pounds to get 165,000 pounds in orbit is a pretty big difference! To be fair, the orbiter can also carry a 65,000-pound payload (up to 15 x 60 feet in size), but it is still a big difference. The fuel weighs almost 20 times more than the Orbiter [source: The Space Shuttle Operator's Manual].
All of that fuel is being thrown out the back of the Space Shuttle at a speed of perhaps 6,000 mph (typical rocket exhaust velocities for chemical rockets range between 5,000 and 10,000 mph). The SRBs burn for about two minutes and generate about 3.3 million pounds of thrust each at launch (2.65 million pounds average over the burn). The three main engines (which use the fuel in the external tank) burn for about eight minutes, generating 375,000 pounds of thrust each during the burn.
Monday, April 5, 2010
Manufacturing Process
Chapter 1
Manufacturing - def - to convert raw material into useful articles with the help of labour or machining.
Chapter 2
Metal casting
Def- of casting- the flow of molten metal into the mould where it solidifies the shape of the mold cavity
Advantage
- Complex shape
- Net shape ability
- very large part
- Variety of metal
- Mass production
Disadvantage
- Poor accuracy
- Poor surface
- Internal defects
- mechanical properties
- environmental impact
Casting technology
Sand casting
Fluilidity
The measure of the capability of a molten metal to flow into the mold cavity before freezing.
Factors effecting fluilidity
1. Pouring temperature
2. Heat transfer
3. Viscosity
4. Metal composition
Riser design
Solidification of metal ( graph)
Solidification of the volume shrinkage (graph)
Shrinkage
Sand casting benefits
1. Cheap casting process
2. Can go up to several tons
3. Cheap machining shapes from bar stock
4. Can be used with most pourable metal and alloy
5. Can intricate shape
The sand casting process
The sand
1. FLOWABILITY
2. PLASTIC DEFORMATION
3. GREEN STRENGTH
4. PERMABILITY
Metal casting
- Shell moulding
- Investment casting process
- Die casting
Molten metal is injected into a closed metal die under high pressure
Pressure maintained during solidification
Die separated and casting ejected
- cold chamber
- hot chamber
Hot chamber
Advantage
- No transfer of molten metal
- Offer fast cycling time
- Good strength product
- Excellent dimensional
Disadvantage
- expensive
- requires high production rates to justify the usage
- cannot be used for high melting point metals
Cold chamber
Advantage
- Good advantage
- Excellent dimensional
- Excellent surface
Disadvantage
- Expensive
- requires high production rates to justify the usage
- The need to transport molten metals
Centrifugal casting
Utilize inertial force by rotation to distribute molten metal into mold cavities.
Process :
Pour molten metal into rotating mould
Metal is held against the mould wall by centrifugal force until it is solidifies
3 types of centrifugal casting
1. True centrifugal casting
2. Semi centrifugal casting
3. Centrifuging
Continuous casting
Fundamental of Metal Cutting
- Plastic deformation in cutting
- Type's of cutting
- Orthogonal cutting => the cutting edge is straight and is set in a position perpendicular to the direction of the primary motion.
- Oblique cutting => the cutting edge is set as an angle, the tool of the cutting edge is inclined , λs.
- Cutting condition
cutting velocity, v
Depth of cut, d
Feed,f
- Chip formation
3 types of chip produced in casting.
1. Discontinuous chip
2. Continuous chip
3. Continuous chip with BUE (build up edge)
Manufacturing - def - to convert raw material into useful articles with the help of labour or machining.
Chapter 2
Metal casting
Def- of casting- the flow of molten metal into the mould where it solidifies the shape of the mold cavity
Advantage
- Complex shape
- Net shape ability
- very large part
- Variety of metal
- Mass production
Disadvantage
- Poor accuracy
- Poor surface
- Internal defects
- mechanical properties
- environmental impact
Casting technology
Sand casting
Fluilidity
The measure of the capability of a molten metal to flow into the mold cavity before freezing.
Factors effecting fluilidity
1. Pouring temperature
2. Heat transfer
3. Viscosity
4. Metal composition
Riser design
Solidification of metal ( graph)
Solidification of the volume shrinkage (graph)
Shrinkage
Sand casting benefits
1. Cheap casting process
2. Can go up to several tons
3. Cheap machining shapes from bar stock
4. Can be used with most pourable metal and alloy
5. Can intricate shape
The sand casting process
The sand
1. FLOWABILITY
2. PLASTIC DEFORMATION
3. GREEN STRENGTH
4. PERMABILITY
Metal casting
- Shell moulding
- Investment casting process
- Die casting
Molten metal is injected into a closed metal die under high pressure
Pressure maintained during solidification
Die separated and casting ejected
- cold chamber
- hot chamber
Hot chamber
Advantage
- No transfer of molten metal
- Offer fast cycling time
- Good strength product
- Excellent dimensional
Disadvantage
- expensive
- requires high production rates to justify the usage
- cannot be used for high melting point metals
Cold chamber
Advantage
- Good advantage
- Excellent dimensional
- Excellent surface
Disadvantage
- Expensive
- requires high production rates to justify the usage
- The need to transport molten metals
Centrifugal casting
Utilize inertial force by rotation to distribute molten metal into mold cavities.
Process :
Pour molten metal into rotating mould
Metal is held against the mould wall by centrifugal force until it is solidifies
3 types of centrifugal casting
1. True centrifugal casting
2. Semi centrifugal casting
3. Centrifuging
Continuous casting
Fundamental of Metal Cutting
- Plastic deformation in cutting
- Type's of cutting
- Orthogonal cutting => the cutting edge is straight and is set in a position perpendicular to the direction of the primary motion.
- Oblique cutting => the cutting edge is set as an angle, the tool of the cutting edge is inclined , λs.
- Cutting condition
cutting velocity, v
Depth of cut, d
Feed,f
- Chip formation
3 types of chip produced in casting.
1. Discontinuous chip
2. Continuous chip
3. Continuous chip with BUE (build up edge)
Sunday, April 4, 2010
Awesome =)
Life is so interesting now. Nothing much to complain about besides MONEY!
So excited! Finally after ages, now I am catching up with all my old friends. We are planning to meet up and I believe there's allot to catch up about all these years. Few of them are already in the verge of marriage. Best wishes and congratulations.
Easter was an awesome one this year. Baked cake for the orphanage. Satisfied!The kids were so adorable!
Preparing for the small test this Wednesday! Hope I'll give my best shot!ere
America here I come =)
So excited! Finally after ages, now I am catching up with all my old friends. We are planning to meet up and I believe there's allot to catch up about all these years. Few of them are already in the verge of marriage. Best wishes and congratulations.
Easter was an awesome one this year. Baked cake for the orphanage. Satisfied!The kids were so adorable!
Preparing for the small test this Wednesday! Hope I'll give my best shot!ere
America here I come =)
Thursday, April 1, 2010
Seven Steps to Better Presentations
I find this tips really effective, I personally tried these tricks on better presentations during my Presentation on power plants generations. Thank you @Prakash Chandran.
Hope this will also help my fellow friends as well.
Here they are:
Seven Steps to Better Presentations
“I’ve noticed a lot of talk about Powerpoint lately. About how it’s so terrible and how it enables awful presentations. But the problem isn’t Powerpoint, of course. The problem is bad content delivered poorly.
I speak for a living, and hear lots and lots of presentations at the conferences I attend. Here are some notes I wrote up for someone who is about to give his first ever public presentation.”
1. Tell stories. Seriously. People could care less about the five ways some XML vocabulary will enable enterprise whatever. Rather, put a screenshot of your project up, tell people what you learned while doing it, then give them a slide that reiterates those ideas in easy to digest bullets. That’s interesting. Even more interesting are before-and-after screenshots. Better yet: a step-by-step evolution. Just do not go from bullet-point slide to bullet-point slide trying to tell people what to think.
2. Show pictures. Got a good metaphor? Use it. “The Web is like a school of fish.” But go to images.google.com and type in “sardines” or “school of fish” or whatever. Make it a slide. Then say the Web is like that. Much more powerful and memorable.
3. Don’t apologize. Ever. If something is out of order, or if something occurs to you as a mistake during the presentation, keep it to yourself. They’ll never know. Besides, nobody cares about the presentation itself. This is really hard, because you know the whole backstory, and you’ll be tempted to explain why something isn’t quite perfect. Skip it. Also, you don’t need to apologize about the color on the projector, or the fact that your mic just popped off your lapel, or that a staff person spilled a pitcher of water. Commiserating is fine, however. “If it gets another 5 degrees colder in here, I’ll be able to see my breath!”
4. Start strong. I can’t believe how many presenters forget this. Do not get up there and say, “Um, well, I guess we should probably get started.” Instead, say, “Hi, I’m Jeff. It’s really great to be here, and thank you so much for coming to my session. Today, we’re going to talk about….” Make sure those are the absolute first words you say out loud. No need for a joke or an opening or any of that. Just start strong and confident.
5. End strong too. “…so that’s why I like social software. I appreciate your attention today. Thank you.” Then stand there and wait. Everyone will clap, because you just told them you were done. When they’ve finished, ask them if they have any questions. If nobody asks anything, break the uncomfortable silence with “Well, I guess I told you everything you need to know then. [heh heh] I’ll be around after if you think of anything. Thanks again!” and start packing up your stuff.
6. Stand. Away from the podium. Out from behind the presenter table. Keep your hands out of your pockets. Take off your conference badge (the lights will catch it and be distracting). I pace a little bit around the stage, timed with my points, saying one thing from over here, and another from over there. But don’t move too much.
7. Pause. When you say something important, leave a gap after it. Let it hang there for a few seconds. Try it when talking to your friends. “You know what I think? (pause…two…three…four…) I think Bush is bankrupting this country for the next twenty years. (pause…two…three…four…) Here’s why…”
Hope this will also help my fellow friends as well.
Here they are:
Seven Steps to Better Presentations
“I’ve noticed a lot of talk about Powerpoint lately. About how it’s so terrible and how it enables awful presentations. But the problem isn’t Powerpoint, of course. The problem is bad content delivered poorly.
I speak for a living, and hear lots and lots of presentations at the conferences I attend. Here are some notes I wrote up for someone who is about to give his first ever public presentation.”
1. Tell stories. Seriously. People could care less about the five ways some XML vocabulary will enable enterprise whatever. Rather, put a screenshot of your project up, tell people what you learned while doing it, then give them a slide that reiterates those ideas in easy to digest bullets. That’s interesting. Even more interesting are before-and-after screenshots. Better yet: a step-by-step evolution. Just do not go from bullet-point slide to bullet-point slide trying to tell people what to think.
2. Show pictures. Got a good metaphor? Use it. “The Web is like a school of fish.” But go to images.google.com and type in “sardines” or “school of fish” or whatever. Make it a slide. Then say the Web is like that. Much more powerful and memorable.
3. Don’t apologize. Ever. If something is out of order, or if something occurs to you as a mistake during the presentation, keep it to yourself. They’ll never know. Besides, nobody cares about the presentation itself. This is really hard, because you know the whole backstory, and you’ll be tempted to explain why something isn’t quite perfect. Skip it. Also, you don’t need to apologize about the color on the projector, or the fact that your mic just popped off your lapel, or that a staff person spilled a pitcher of water. Commiserating is fine, however. “If it gets another 5 degrees colder in here, I’ll be able to see my breath!”
4. Start strong. I can’t believe how many presenters forget this. Do not get up there and say, “Um, well, I guess we should probably get started.” Instead, say, “Hi, I’m Jeff. It’s really great to be here, and thank you so much for coming to my session. Today, we’re going to talk about….” Make sure those are the absolute first words you say out loud. No need for a joke or an opening or any of that. Just start strong and confident.
5. End strong too. “…so that’s why I like social software. I appreciate your attention today. Thank you.” Then stand there and wait. Everyone will clap, because you just told them you were done. When they’ve finished, ask them if they have any questions. If nobody asks anything, break the uncomfortable silence with “Well, I guess I told you everything you need to know then. [heh heh] I’ll be around after if you think of anything. Thanks again!” and start packing up your stuff.
6. Stand. Away from the podium. Out from behind the presenter table. Keep your hands out of your pockets. Take off your conference badge (the lights will catch it and be distracting). I pace a little bit around the stage, timed with my points, saying one thing from over here, and another from over there. But don’t move too much.
7. Pause. When you say something important, leave a gap after it. Let it hang there for a few seconds. Try it when talking to your friends. “You know what I think? (pause…two…three…four…) I think Bush is bankrupting this country for the next twenty years. (pause…two…three…four…) Here’s why…”
Canon PowerShot SD3500 Digital Camera
Canon PowerShot SD3500 Digital Camera
The Canon PowerShot SD3500 digital camera boasts an innovative 3.5" touch screen, optical image stabilization and smart auto mode but Chris Hardwick and Alison Haislip find out if these features are worth the $330 cost.
Find the full review from Gadget Pron on Attack of the Show after the cut.
What You Need To Know
The camera measures about 4" across and is under 1" thick.
It might be bigger than most cameras you are used to.
This camera features a much improved touch screen.
It's much more responsive and acts the way you'd expect it to.
Just tap on your subject to auto-focus.
There are also tactile controls like tapping the camera to start a slide show, and tilting it to move to the next image.
overall, the experience is much better.
They added a few features like Creative Effects and Smart Shutter (which takes a picture when you smile or wink), all of which work well for the most part.
The effects like fish-eye and miniature are fun to have, and really do add value.
Most of the time, effects on digital cameras are worthless.
Smile shutter works like a charm, but the wink timer has trouble detecting whether or not you're closing your eye.
Canon was close to make their pictures look just as good as their previous point-and-shoot cameras.
Normal light pictures have a lot of detail and accurate colors, but they don't pop like we're used to seeing.
Low light pictures look good, too, but occasionally, you might get a little too much noise or soft focus.
Most of the time, images are super clear.
Price
$330
Rating
3 Seals of Approval out of 5 (How do we rate gadgets?)
The camera is good in many respects, but the super high price and barely above average image quality means you'll have to decide for yourself on whether or not this is a buy.
The Canon PowerShot SD3500 digital camera boasts an innovative 3.5" touch screen, optical image stabilization and smart auto mode but Chris Hardwick and Alison Haislip find out if these features are worth the $330 cost.
Find the full review from Gadget Pron on Attack of the Show after the cut.
What You Need To Know
The camera measures about 4" across and is under 1" thick.
It might be bigger than most cameras you are used to.
This camera features a much improved touch screen.
It's much more responsive and acts the way you'd expect it to.
Just tap on your subject to auto-focus.
There are also tactile controls like tapping the camera to start a slide show, and tilting it to move to the next image.
overall, the experience is much better.
They added a few features like Creative Effects and Smart Shutter (which takes a picture when you smile or wink), all of which work well for the most part.
The effects like fish-eye and miniature are fun to have, and really do add value.
Most of the time, effects on digital cameras are worthless.
Smile shutter works like a charm, but the wink timer has trouble detecting whether or not you're closing your eye.
Canon was close to make their pictures look just as good as their previous point-and-shoot cameras.
Normal light pictures have a lot of detail and accurate colors, but they don't pop like we're used to seeing.
Low light pictures look good, too, but occasionally, you might get a little too much noise or soft focus.
Most of the time, images are super clear.
Price
$330
Rating
3 Seals of Approval out of 5 (How do we rate gadgets?)
The camera is good in many respects, but the super high price and barely above average image quality means you'll have to decide for yourself on whether or not this is a buy.
Whats happening!
I know It has been sometime since I last Blogged.
I was happy that I could hunt back my old 'skool' friends.
It has been sometime since I last meet them all up.
Its Easter, great feeling. I'm into fasting, 'oh well it's just for a day'
We're thinking of some charity to carry on this weekend. I and the girl's going to bake cake *back-to-back*
It's going to be an awesome one, because we have decided to bake those cake for the orphan kids. And of coarse Egg painting will be on and following by our all time BBQ party!
Excited though.
At the same time - bloody exams around the corner, many sleepless night.
Will upload more of the current event soon =)
I was happy that I could hunt back my old 'skool' friends.
It has been sometime since I last meet them all up.
Its Easter, great feeling. I'm into fasting, 'oh well it's just for a day'
We're thinking of some charity to carry on this weekend. I and the girl's going to bake cake *back-to-back*
It's going to be an awesome one, because we have decided to bake those cake for the orphan kids. And of coarse Egg painting will be on and following by our all time BBQ party!
Excited though.
At the same time - bloody exams around the corner, many sleepless night.
Will upload more of the current event soon =)
Friday, January 8, 2010
Kick start 2010
Kick start of 2010, started As a great big challenging year. Thinking back of 2009 it was an awesome and a wonderful year that I can never forget for the entire of my life. Was filled with alot of love, hatred, betrayal,happiness, joy, tears, smile, party's, hangovers, family, big buck. Missing those days of 2009 but did spent the best minutes of 2009. NO REGRETS!
2010, started this year with plenty of sweet memories.
started this year with a slogan ' live like we're dying' okay I know its a songs title of KRIS ALLEN but did inspire me much.
Certainly, the reason to start writing blog of myself is because with the today's busy world, the people use to be around me are now far at some other continent.
Friends,family also my cousins are now all busy, so to keep my 'people' updated with me!
We still have Facebook but seriously i find it as a very dangerous hub. I will update my blog time-to-time.
HAPPY NEW YEAR!!
2010, started this year with plenty of sweet memories.
started this year with a slogan ' live like we're dying' okay I know its a songs title of KRIS ALLEN but did inspire me much.
Certainly, the reason to start writing blog of myself is because with the today's busy world, the people use to be around me are now far at some other continent.
Friends,family also my cousins are now all busy, so to keep my 'people' updated with me!
We still have Facebook but seriously i find it as a very dangerous hub. I will update my blog time-to-time.
HAPPY NEW YEAR!!
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