When a golf ball is struck, the kinetic energy of the club works to flatten the ball. During the instant that the ball is deformed the ball has acquired potential energy. Then as the ball's molecules return to their normal uncompressed form, they richochet the ball forward, and potential energy is converted back into kinetic energy.

When a man climbs with a ball to the top of a mountain, he converts food energy into mechanical energy. At the summit, the motionless man and ball have gravitational potential energy defined as mgh, where m=mass; g= gravity and h=height. If pushed, the ball rolls down the hill, and potential energy gets converted into energy of motion.

The unstable compound NI₃ is like the deformed golf ball or the ball at the summit of a mountain. Literally, with the touch of a feather, part of the energy stored in the bonds between nitrogen and iodine is released; elemental iodine and nitrogen gases expand violently. The energy that had been invested in nitrogen triiodide was far in excess of what was needed to make the new products.The excess potential energy is converted into molecular motion and heat.

photo by Journal of Chemical Education