# If an object falls - regarding air resistance - does the Potential or Kinetic energy get converted into thermal energy as it is falling?

I read a paragraph on the transfer of potential energy to kinetic energy and heat from this website:

Even if air resistance slows down the ball, the potential energy is the same (Mb x g x H). But if air resistance is in the way, not all of the potential energy can be converted to kinetic energy. Some of the energy has to be used to push the air molecules out of the way. When that happens, the energy of the air molecules is increased. The air is actually "heated" up by the falling ball.

This text indirectly mentions that the Potential Energy gets converted into heat. However my common sense (for lack of a better term) makes me think that the Potential Energy gets converted into Kinetic Energy which in turn gets converted into Thermal energy. Would someone be able to enlighten me on this please?

Also, as a side question, it isn't called Heat Energy right? A lot of websites seem to be saying that, but heat is just the transfer of Thermal Energy...

• Heat Energy, Thermal Energy - the same thing. Energy manifested in the form of particle motion. The higher the mean particle velocity, the more heat you have and thus a higher temperature. In the end we still don't know what energy 'is'. We only know it's something 'conserved' and we give it many names according to how it manifests itself in space and time. – docscience Jan 11 '15 at 21:12
• It isn't only the air that heats up. the ball gets hotter too. So some of the potential energy is going to heating of the ball. – Peter R Feb 9 '16 at 20:32
• To give some intuition and to answer the question, it is kinetic (u can tell since the drag term always is a function of the velocity explicitly) microscopically see it as the velocity of the shear air is causing the molecules on the side of the object to vibrate vigorously – Russell Yang Mar 11 '17 at 2:51

The friction with the air indeed slows down the falling ball. The friction is minimal if the ball stays in place (i.e. there may be only some friction due to air currents.) But if the ball moves the friction is bigger because as the ball moves, it pushes away the air molecules to make room. The friction opposes the ball movement. So, indeed, the heating takes from the kinetic energy through friction, not from the potential energy. The meaning of the text, as I understand, it that, bottom line, the kinetic energy acquired by the ball during its fall is not equal to the total potential energy $M_b gH$.
• 1) Welcome to SE! 2) you can edit your answer (the edit button at the bottom of your post) to fix the unfinished sentence 3) you say that KE is converted into heat, and not PE. Could you elaborate on this, please? I mean, can you explain the reasoning behind your statement? – AccidentalFourierTransform Feb 9 '16 at 20:26