Fountain in the sink

My five-year-old called my attention to this interesting little phenomenon when he was supposed to be washing his face.  The water from the faucet hits the sink, and spurts up again in a little fountain.

When he noticed this little scene, my son was quick to say, "I don't know why that happens."   I hope he is always quick to recognize what is beyond his knowledge.  It is a wisdom that leads to greater understanding, and an example I want to follow.

I reminded him of our bumper car activity earlier in the week and asked what happened when a very little car, hit a big one.  "It bounced off."  The same thing is happening here. All those little water molecules are bouncing off of the big sink.  The force of the tiny molecules on the big sink is not enough to significantly move the sink, but the force of the sink on a tiny molecule makes it jump back into the air.  The momentum that the molecules have going into the collision is conserved although redirected.  As the sink fills, the water molecule interact with each other more and more, rather than the sink, and the fountain dies down.

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