Today as I was rushing out of the house to my car, I dropped my water bottle on my driveway. As it hit the floor and bounced back up to me, I realized that it was an inelastic collision!! Actually my first thought was to get it from under the car so I could take it to school, but that's besides the point. Anyways, I knew it was an inelastic collision because some of the energy the water bottle started with, which was all potential energy because it was not in motion yet, was changed into sound energy as well as the energy used to create a dent in the bottle. So, the water bottle starts off with PE=mgh then is dropped and the energy changes into kinetic. When it hits the floor, the loss of energy is experienced as the bottle is deformed and the noise is heard. Due to conservation of energy, the bottle keeps some energy as not all of it is dissipated which is why it bounces back up off the ground.