Science Questions

Some scientific friends of mine assured me that a bullet fired from a rifle held horizontally will hit the ground at exactly the same time as a bullet from a rifle held vertically, pointing at the ground.

Sun, 2nd Nov 2008

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Question

Edwin asked:

My question is about rifles and bullets. Some scientific friends of mine assured me that a bullet fired from a rifle held horizontally will hit the ground at exactly the same time as a bullet from a rifle held vertically, pointing downwards. Fair enough, Iím a linguist. I was rotten at science but that seems to defy common sense.

Answer

Dave - This is a mangling of quite a famous experiment. What the actual thing they should have told you is that if you fire a rifle horizontally and drop the bullet from the same place at the same time then theyíll both hit the ground at the same moment.

Chris - So youíve got a bullet in one hand, rifle in the other. You fire the gun at the same moment you let go of another bullet from your hand. The two bullets should actually hit the ground...

Dave - At exactly the same time. If thereís no air resistance basically how fast youíre going horizontally has no relationship to how fast you accelerate downwards. The bullet which is moving and the one which is accelerating downwards both move at exactly the same speed. Theyíll both hit the ground at the same time. If you take a gun and fire it straight downwards then the bulletís going to come out of the gun at several hundred metres per second. Itís going to hit the ground far quicker than the one you fire horizontally.

Chris - We did an amazing experiment at school which I remember to this day which shows how good this experiment was: the monkey and hunter experiment. We had a sort of blow-pipe with tinfoil across the end of the blow pipe which was making an electrical contact to an electro-magnet that was holding a tin can at a distance. A ball bearing was put into the glass tube. You blow down the glass tube so the ball bearing leaves the blow pipe, breaking the piece of foil in the process. Therefore it cuts the supply to the electromagnet. The tin can starts to fall at exactly the same rate as the ball bearing leaves the tube. If all things are equal, i.e. the can is being accelerated down by gravity at the same rate as the ball bearing is being accelerated down by gravity the two will hit each other. They always do. Itís called the monkey and hunter experiment because the idea is that the monkey is dangling in the distance on a tree and the person fires the gun. Assuming it takes no time for the gun discharge to reach the monkey. The monkey lets go of the tree and starts to drop at the same minute the bullet leaves the gun. Therefore the bulletís falling and the monkeyís falling and they should still reach each other. Itís a very elegant way of explaining it.

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