"Always vote for principle, though you may vote alone, and you may cherish the sweetest reflection that your vote is never lost." -- John Quincy Adams
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There was an awsome book written a couple of years ago called the Science of Superman. It examined the legends behind each of his superpowers and how the laws of physics could or could not support them. The book was geared toward finding ways to make the powers conform to the laws of physics. It was fascinating.
Doug
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How does Superman achieve this initial velocity of more than 200 feet/sec? Through a mechanical process that physicists term “jumping.” Superman crouches down and applies a large force to the ground, causing the ground to push back (since forces come in pairs, according to Newton's third law). As one would expect, it takes a large force in order to jump up with a starting speed of 140mph. To find exactly how large a force is needed, we make use of Newton's second law of motion, F = ma —that is, Force is equal to mass multiplied by acceleration. If Superman weighs 220 pounds on Earth, he would have a mass of 100 kilograms. So to find the force, we have to figure out his acceleration when he goes from standing still to jumping with a speed of 140mph. Recall that the acceleration describes the change in velocity divided by the time during which the speed changes. If the time Superman spends pushing on the ground using his leg muscles is 1/4 second, then his acceleration will be the change in speed of 200 feet/sec divided by the time of 1/4 second, or 800 feet/sec 2 (approximately 250 meters/sec 2 in the metric system, because a meter is roughly 39 inches). This acceleration would correspond to an automobile going from 0 to 60mph in a tenth of a second. Superman's acceleration results from the force applied by his leg muscles to get him airborne. The point of F = ma is that for any change in motion, there must be an applied force and the bigger the change, the bigger the force. If Superman has a mass of 100 kilograms, then the force needed to enable him to vertically leap 660 feet is F = ma (100 kilograms) x (250 meters/sec 2 ) = 25,000 kilograms meters/sec 2 , or about 5,600 pounds.
Is it reasonable that Superman's leg muscles could provide a force of 5,600 pounds? Why not, if Krypton's gravity is stronger than Earth's, and his leg muscles are able to support his weight on Krypton? We calculated that when making his greatest leap, Superman's legs must provide a force of 5,600 pounds. Suppose that this is 70 percent larger than the force his legs supply while simply standing still, supporting his weight on Krypton. (This is being generous, as when most people jump they can only apply a force approximately equal to their standing weight.) In this case, Superman on his home planet would weigh 3,300 pounds. His weight on Krypton is determined by his mass and the acceleration due to gravity on Krypton. We assumed that Superman's mass is 100 kilograms, and this is his mass regardless of which planet he happens to stand on. If Superman weighs 220 pounds on Earth and nearly 3,300 pounds on Krypton, then the acceleration due to gravity on Krypton must have been 15 times larger than that on Earth.
So, just by knowing that F = ma , making use of the definitions “distance5speed3time” and “acceleration is the change in speed over time,” and the experimental observation that Superman can “leap a tall building in a single bound,” we have figured out that the gravity on Krypton must have been 15 times greater than on Earth .
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"Always vote for principle, though you may vote alone, and you may cherish the sweetest reflection that your vote is never lost." -- John Quincy Adams
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