i'm currently discussing this with a friend. anyway. here is the conversation: he said It started as "If something doesn't have a mass, it cannot have a force", due to Newton's second law, F = ma (Force = Mass x Acceleration). Logically, if you substitute 0 in for the Mass, you will get a result of 0 Force. My brother then argued that there are things which have no mass but still have a force and the main example we discussed was wind. Does wind have a mass? After a while we got to the fact that wind is just heat. After long debating about "does heat have mass" we got to the fact that heat is just energy. Now we are at "does energy have mass". Apparently there are conflicting arguments all over the place with this. I believe for there to be energy, it must have mass, due to Einstein's formula E = mc^2 (Energy = Mass x Speed of Light^2). As with F = ma, if you substitute 0 in for the Mass, you will get a result of 0 Energy. My thinking: my understanding is that hot air rises because it is less dense than air that is colder. which is a change in pressure, which is what causes air particles to move. hence wind. so heat causes wind but that doesnt mean wind is heat. is my understanding screwed? my understanding of heat is that it is a form of energy and that heat does not have a mass and that there must be a flaw in his logic of wind being heat. So i said that he is overcomplicating things and that the air particles have a mass. he said: Well yes, but the thing moving that air... does it have a mass? Because it is able to move the air, meaning it exerts a force, which Newton's Second Law tells us must mean it has a mass. Although this heat, as I said, energy, so the question is, does energy have mass...? So he doesn’t actually want to know about wind but the force on wind. i asked him how wind was heat and he couldn’t remember. so the force that causes wind is the force that causes heat i guess. unless the name of that force is wind. in which case I’m thoroughly confused. I think I need a scientific definition of wind here so now i'm asking you about your opinion of the force that causes wind being heat and how heat is energy and about the force that causes heat And also I guess this could be related to convection currents.