Question

When your hands are cold, you can rub them together to warm them. Explain the energy transformations that make this possible.

Answer 1

When we eat out food the chemical energy which we get from our food enables us to do work. This chemical potential energy enables us to rub our hands, i.e., chemical potential energy is converted to kinetic energy. Due to rough surface of our hands a friction force exists which opposes the motion and this friction force converts the kinetic energy to thermal energy which gives us heat and warmth.