Physics 2000 Einstein's Legacy Microwave Ovens

Water and Friction

The rotating water molecule always looks sluggish, like it's trying to move through goo.

Remember back to when we said that motion leads to friction, and then friction leads to heating?

Yeah, I guess.

You are seeing the effects of friction. Since the water molecule slows down in its rotation, there must be friction forces. These forces produce heat energy.

So where does the force of friction come from?

Going back to the compass, there is friction at the point where the needle is connected to the rest of the compass. And sometimes they fill the compass with oil, which will also damp the motion.

And for water?

The friction comes from the other molecules. In a liquid the water is free to bump into anything around it. And there is a lot to bump into in a liquid. For more information on collisions, click here.

By changing the density of the water molecules, you are changing the friction between them.

When the density is all the way down, the water molecule goes wild. Cool.

If there are no other water molecules or anything else around, there is no damping.