Energy in 3 consecutive forms: potential, kinetic, internal
(Photo credit: Wikipedia) A rock has potential energy (PE)
localized in it when you lift it up above the ground. The rock
is the system; everything else it encounters is the
surroundings. Drop the rock and its PE changes to kinetic energy
(energy of movement, KE), pushing air aside as it falls
(therefore spreading out the rock’s KE a bit) before it hits the
ground, dispersing a tiny bit of sound energy (compressed air)
and causing a little heating (molecular motion energy) of the
ground it hits and in the rock itself. The rock is unchanged
(after a minute when it disperses to the air the small amount of
heat it got from hitting the ground). But the potential energy
that your muscles localized in by lifting it up is now totally
spread out and dispersed all over in a little air movement and a
little heating of the air and ground. A hot frying pan? The iron
atoms in a hot frying pan (system) in a room (surroundings) are
vibrating very rapidly, like fast