Mechanical heat energy initiated by movement between objects in contact with one another defines which concept?

• A. Heat of fusion
• B. Heat of vaporization
• C. Heat of friction
• D. Sensible heat

Answer: (C)

Frictional heat is the idea here: when two objects in contact move against each other, mechanical energy from that motion is converted into thermal energy, warming the surfaces and surrounding material. This is the heat produced specifically by the interaction of rubbing surfaces, which can raise temperatures and potentially ignite combustibles if enough energy is generated.

Heat of fusion and heat of vaporization describe energy required for phase changes (melting and boiling), not the ongoing conversion of mechanical energy from sliding into heat. Sensible heat refers to heat that changes temperature without a phase change, but frictional heating is distinct because it centers on the mechanism—friction between moving surfaces—rather than just a temperature change or a phase change.