when something is dropped, its potential energy is turned into kinetic energy. as the object stops [as if it is bouncing back up and starting to slow to fall back down] kinetic energy decreases and becomes potential energy again. the energy of a system is the total kinetic plus potential, so whatever isnt kinetic energy is potential energy [and vice versa]. the same principle applies for spring systems. i hope this helps. sorry if its confusing. kake~<3
