Physics Question #1356

Jennifer Easterly, a 23 year old female from Sydney, NS asks on March 28, 2003,

What happens to a bullet fired straight up into the air? Does gravity eventually slow it down so it comes back to Earth? And if so, will it disintegrate before it hits the ground (or, theoretically, someone)?

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The answer

Barry Shell answered on March 28, 2003

It doesn't have enough velocity to escape Earth's gravity. An object must have a speed of about 40,200 km/h at the surface of the Earth to break free of the pull of gravity. Even the most powerful rifle has a muzzle velocity (the speed of the bullet as it leaves the end of the gun) of about 3,000 km/h so this is far short of the requirement.

On its way back the bullet probably will not disintegrate because it will not have gone high enough, and on re-entry it will not reach speeds great enough to cause a sufficient amount of friction to burn up. The bullet will hit the ground, and hopefully not a person.

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