most materials B) Expand when thermal energy is added. For example, if you have a ping pong ball that has a dent in it and you put it in boiling water, after a few minutes the dent will disappear, meaning the ball expanded. the reason why this happened is because the ping pong ball is hollow inside and the air inside heats up and it makes the particles bounce harder against the ball's inside and that makes the ball's dent rise and disappear.