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Presenter Greg Foot investigates what would happen if an asteroid collided with Earth. He calculates how much energy would be transferred at impact using the formula E = 陆mv2 and produces an equivalent explosion to show the size of crater produced by a meteoroid the size of a golf ball. He explains why the size and speed of asteroids matters and how our atmosphere protects from all but the largest asteroids.

Greg does this by showing how air pressure alone can be used to ignite cotton wool and how air and friction cause objects smaller than 35m in diameter to burn up as they enter the Earth鈥檚 atmosphere before reaching the Earth鈥檚 surface. Unlike the Earth, the Moon has no atmosphere and this is why the Moon has a history of more numerous impacts.