Why does rubbing your hands together make them warmer?

Friction causes the hands to warm up when rubbed together. The greater the amount of friction between two objects is, the more heat is generated.

Friction is a force, and it tries to prevent objects from moving. Friction has benefits as well as negative consequences. This force exists in all mechanical objects where two or more moving parts have contact with each other. This causes parts to break down quickly unless a lubricant is used to reduce the friction. The friction between a car's tires and the road is the primary reason a car doesn't slide on a wet road or while going around a corner.