On every flight pilots are exchanging types of energies.

Three forms used in everyday flying are:

Chemical energy (CE) in the form of fuel to offset drag.

Kinetic energy (KE) from motion  = 1/2mV2 (V squared).

Potential energy (PE) from height and gravity = mgh.

m=mass, V = velocity, g = gravitational constant, h = height

A child on a swing is a good example of transfer between energy types.

When the parent pulls the child in the swing back to a high point, chemical energy (CE) has been used (via the parent’s muscles) to increase the potential energy (PE) of both the child and the swing seat and chain. Releasing the swing starts a conversion of PE to kinetic energy (KE) due to gravity. As the swing arc bottoms out, PE is zero and KE is at its maximum. The movement back upward then converts the KE back to PE. The journey downward will begin as the kinetic energy reaches zero and the PE its maximum. The system could theoretically go on forever, except for air resistance (drag) of the child and swing and the energy loss of the system due to friction at the pivot points. If a second child walks into the path of the first, energy will be transferred to child #2 in the form of KE, and possibly PE, depending on the second child’s trajectory. The swinging child will experience a loss in kinetic energy due to the impact and the transfer of energy. The parent will then convert chemical energy into kinetic energy rushing to check on the downed child, who will be changing CE in chest, lungs, and vocal cords into the kinetic energy of sound waves.

A plane in a constant airspeed glide is exchanging potential energy to overcome drag. As the flare is started, kinetic energy is given up to reduce the need for potential energy sacrifice (the round-out). This kinetic energy give-away will accelerate as drag (induced) increases, somewhat offset by ground effect. With luck, the exchange works out perfectly and a “grease-job” results.