On a chilly day, you can rub your hands together to warm them. Why does rubbing your hands make them warm?
You are made up of molecules, just like all the other kinds of matter around you.
When you rub your hands together, you create friction. You make the molecules in your skin bump and push one another.
That makes the molecules speed up. It gives them more energy. The faster the molecules move, the warmer you get. So if you rub hard enough, your hands feel warm.
Picture Credit : Google