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Mumbai SSC and HSC Time Table for March 2009 |
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Written by Santosh Mishra
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Saturday, 24 January 2009 |
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Last Updated ( Saturday, 24 January 2009 )
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Written by Santosh Mishra
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Wednesday, 28 March 2007 |
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An airplane supports itself in flight by deflecting the passing airstream downward. The plane's wings push this airstream downward and the airstream reacts by pushing the wings upward. This action/reaction effect is an example of Newton's third law of motion, which observes that forces always come in equal but oppositely directed pairs: if one object pushes on another, then the second object must push back on the first object with a force of equal strength pointing in the opposite direction. Even air obeys this law so that when the plane's wings push air downward, the air must push the wings upward in response. In level flight, the deflected air pushes upward so hard that it supports the entire weight of the plane. Just how the airplane's wings deflect the airstream downward to obtain this upward lift force is a marvel of fluid dynamics. We can view it from at least two perspectives: a Newtonian perspective which concentrates on the accelerations of the passing airstream and a Bernoullian perspective which concentrates on speeds and pressures in that airstream. |
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Last Updated ( Saturday, 24 January 2009 )
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Why do things such as sneakers, T-shirts, and nailpolish change color in the sun? |
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Written by Santosh Mishra
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Wednesday, 28 March 2007 |
Sunlight consists not only of light across the entire visible spectrum, but of invisible infrared and ultraviolet lights as well. The latter is probably what is causing the color-changing effects you mention. Ultraviolet light is high-energy light, meaning that whenever it is emitted or absorbed, the amount of energy involved in the process is relatively large. Although light travels through space as waves, it is emitted and absorbed as particles known as photons. The energy in a photon of ultraviolet light is larger than in a photon of visible light and that leads to interesting effects. |
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