Identify the energy changes in each of the following examples

Pounding a fist on a table

Raising your fist increases the potential energy of your fist as you plan to strike downwards. The potential energy is converted into kinetic energy as you lower your fist to the table. Finally, the kinetic energy of your fist is converted into thermal energy (yes, it sounds weird, but whenever there is physical contact, there is an exchange of heat energy) when you pound the table.