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Q & A: Falling bullets

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Most recent answer: 10/22/2007
Q:
Getting Back to Bullets! If a bullet is shot into the air... and falls back down slower, could it still injur someone if it hits them falling back down?
- Roni
A:
Yes, a bullet shot up into the air will encounter air resistance on the way up, which resists its upward motion. It also encounters resistance on the way down, resisting its downward motion. Both of these effects result in a slower bullet speed when it returns. Nonetheless, many of these bullets are still traveling fast enough to kill. Each year, people die on New Year's Eve because stray bullets from celebrants' gunfire strike them.

The actual speed of the returning bullet depends on a lot of things. In the absence of air resistance, the speed of the bullet out of the gun will be the same as it is coming back down, and so the muzzle velocity of the bullet affects its return speed. Also, the shape of the bullet affects the air resistance. Winds may blow the bullet off course but probably not change the speed noticeably. If the bullet is very dense (and many are made of lead), the air resistance will change its speed less than if it were less dense (as in a rubber bullet).

Tom

(published on 10/22/2007)

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