How do rocks skip on water when thrown?
In: Physics
Usually they spin which makes them less likely to turn any other way, and then they get pushed (thrown) very fast. Good skipping rocks are curved all around usually, so it’s like hitting the water at an angle. Because of these things and probably surface tension too, when the stable, fast, rock slaps the water, it slaps back and makes the rock go back up a bit.
If something is moving quickly enough when it hits the surface of the water, the force of the impact is actually reflected by the surface of the water, rather than absorbed and submerged. Because the stone is spinning very quickly (angular velocity), it doesn’t need to be flying through the air (linear velocity) as quickly to achieve this because the rotation of the stone is generating enough force to compensate for a slower flight.
A smooth stone is also really important because the smooth, rounded stone helps to preserve surface tension in the water. If a sharp edge or spiky point hit the water instead, all of that force would be focused in a very small surface area that would punch right through the surface (Look up bodkin arrows if you want a good example of how low surface can amplify force).
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