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I recall a science exercise where it was said that if you drop a bullet from outside the barrel of a rifle at the same time as you pull the trigger, the fired bullet and the droped bullet will hit the ground at the same time.
Yup, that's right.
Quote:What I want to know is the proof of this premise. Any other conditions? Does it have to be in a vaccuum? Does the rifle velocity have anything to do with it? Does the bullet size or shape? We know the fired bullet is subject to gravity as well as the droped bullet. What else?
Objects only CHANGE their motion in response to forces that are applied to them. Period.
What forces are applied to a bull when you drop it? Just one force: gravity, pulling it down. This speeds up descent downwards from an initial speed of 0.
What forces are applied to a bullet that has been fired from a gun? Gravity, pulling it downwards. There is NO force in the direction that it is being shot. There was a quick initial impulse force from the explosion, which initially sped the bullet up from 0 in the horizontal to 900-3000 FPS in the horizontal...but after than first split second, there is no more force.
Technically, there are some forces pushing in the opposite direction of the bullet speed...basically drag force, which slows down the bullet.
In the downward direction, there is still only one force: gravity. It pulls the bullet down towards earth at the same speed as if it weren't moving horizontally.
Other conditions? Assume a spherical bullet, assume no drag...