# How/why to bullets bounce off water?

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Saw a video of bullets being shot at an angle on a lake and them flying right up. I know nothing about guns and very little about physics. HOW??

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If I throw a rock at water in will go into the water. If i throw a rock across the surface of the water it will skip. A bullet does the exact same thing.

It all comes down to conservation of momentum. An object in motion tends to remain in motion unless acted on by an outside force. So if a bullet is traveling across the surface of a lake it will continue to do so unless a force opposes it. If it is fired into the surface at an angle where it is mostly going across the surface and only a bit down, then the water will oppose the downward movement but there will be enough horizontal movement to let it keep moving across the water.

The result is that the bullet will “bounce” off the surface of the water. In reality of course it is a complex interaction of fluid flow, hydrodynamics, etc. but the takeaway point is that opposing the momentum downward doesn’t make the horizontal momentum vanish.

It takes time for water to flow. If you’re going really fast, then the water can’t get out of the way quickly enough. The water will behave like a solid to you. Bullets tend to be going VERY fast so they bounce off the solid (to them) surface of the water.

Barefoot water skiers make use of this. If you’ve seen on of them fall, they do not just sink into the water. They’ll skid across the surface of the water until they slow down enough to sink.