how is it possible that rubbing a piece of metal on emery pa

how is it possible that rubbing a piece of metal on emery paper can result in an increase in the temperature of the metal? how is it possible that running electric current through a piece of metal can result in an increase in temperature? in each case, what is being transferred to the metal?

Solution

When the metal is rubbed across emery paper, there is friction that comes into play, resisting the motion. Hence as a result of that friction some energy is dissipated as heat. The force of friction due to that movement has to be nullified, so that total energy of the whole system remains constant. So that is attained by releasing the energy as heat.

Also when electric current is passed through a piece of metal, the energy that is imparted to the metal is dissipated as heat as a result of internal resistance of the metal.