Question

Why do our hands get heated while we rub each other

Answer 1

It is due to the frictional force existing . When we rub two surfaces over each other, even it be our hands, frictional force will arise between them. This force will produce heat. Due to the heat loss due to friction in machines, we use various methods like ball bearings, lubricants etc to reduce it.

Answer 2

When we rub our two hands each other , our hands come into contact and generates friction.
Friction creates heat . So, our hands too get heated .