What is the explanation for stones skipping off the water surface? What makes a liquid act as a solid? Is it possible to accelerate water so that it would act a solid body?

Question

anonymous · Answer

Force = mass times acceleration

The flat stone is trying to accelerate the water it contacts, and the force needed may be greater than what is needed to keep the stone from penetrating the water.

anonymous · Answer

It is the impulse provided by the surface tension of the water that makes the stone bounce. Surface tension is an effect of the cohesive property of liquids say water in this case. The mutual attraction of water  gives rise to surface tension creating a visual that there is layer of covering on water. It is a very weak force but it can have disastrous effects when it provides instantaneous change in momentum(impulse) for example when you fall from a great height you exert a great force on the water and it provides an impulse to oppose you motion.

anonymous · Answer

Usually it is barely strong enough to withstand an insect crawling on it. The liquid layer can act as a solid when the force applied on it is very huge and in a very short period of time(instantaneously). Thats why after a certain height it hardly makes a difference whether you fall into a lake or on plain ground. Its going to kill you anyway.

anonymous · Answer

Hmm, so it turns out it is all up to hydrogen bonding. What if intermolecular interactions were weaker? 

The force the object exerts on the surface has a reactive force that causes it to change the direction of the velocity? Is that right?

anonymous · Answer

Yes. It will not change the direction of velocity since the impulse is only instantaneous and it takes time to change velocity.(in the free fall case). And consider it to be something like a normal force which acts on you only when you are in contact with the surface.(A water strider insect can walk on water)

anonymous · Answer

Thank you all for the replies!

anonymous · Answer

I doubt some of what precedes, but never mind. Another factor is the layer of air that is caught between the water surface and  the stone surface, providing some elasticity.

anonymous · Answer

Okay, maybe I missed something. So, the surface tension vector is pointed upwards. The stone arrives at a given angle, and at the point of contact, we have the sum of the impulse, surface tension, friction, elastic forces, and the resultant is pointing away from the surface, sending the stone back in the air. Is that correct?