What is heat?

• A. The speed at which energy is transferred between objects.
• B. The measure of how hot something is.
• C. A form of energy that is transferred by a difference in temperature.
• D. The thermal energy contained in a body.

Answer: (C)

Heat is the energy in transit between objects because of a temperature difference. It’s not the temperature itself, nor the total thermal energy stored inside a body, but the transfer of energy from hotter regions to cooler ones. The statement that defines heat as a form of energy that is transferred by a difference in temperature captures this idea: heat describes the process of energy moving due to temperature differences. The other ideas mix up what heat is: measuring how hot something is refers to temperature, while the thermal energy inside a body refers to internal energy, not the transfer process. The notion of how fast energy is transferred describes the transfer rate (power), not heat itself. In practice, heat can move by conduction, convection, or radiation, and is measured in joules (with the rate of transfer described in watts).