a transfer of energy causing particles to create friction which then causes heat *the earth science definition*- The average Kinetic energy of a substance. Kinetic energy is energy at motion....
This question is so short that it's not completely clear exactly what the questioner is after, but I guess they want to know how to convert heat energy to mechanical energy. There are many machines...
Heat energy is, to an extent, unusable energy. If you have a heat DIFFERENCE, you can convert part of the heat energy - but only part of it - to other kinds of energy. That part, you can of course...