In Joule’s famous experiment where he determined the specific heat capacity of water, he used a paddle to increase the temperature of the water. That is, the kinetic energy of the paddle went into the thermal energy of the water. My question is exactly how did the paddle’s kinetic energy become the water’s thermal energy? Was it because
- The paddle experienced resistive forces in the fluid that dissipated its energy, much the same way friction converts mechanical energy into thermal energy?
- The paddle exerted a force on the fluid particles that caused them to move in the same rotational motion as the paddle, thus imparting kinetic energy to them (i.e. increased internal energy)?