More on Gravity and Orbits An interesting and fun site with Orbital simulations . Pull what you can from it. Basics of Space Flight, Chapter 3. We have a good sense of matter and energy from our everyday experience. Energy is what makes matter move.
Potential energy is energy being stored for later conversion into kinetic energy.
Kinetic energy is energy of motion. A ball has gravitational potential energy when it sits on a ledge. When it rolls off, that potential energy is gradually converted to kinetic energy as it falls. When the ball hits the floor, all of its energy is in the form of kinetic energy. Into thermal energy heating the ball as it compresses and heating the floor.