Mechanical heat energy initiated by the movement between objects in contact with one another is:

• A. Dielectric heating
• B. Heat of friction
• C. Static electricity
• D. Resistance heating

Answer: (B)

Frictional heating occurs when moving contact between surfaces converts kinetic energy into thermal energy. As the surfaces rub, the friction force resists motion and does work on the materials, and that work appears as heat. The amount of heat generated is roughly the friction force times the sliding distance, so more intense rubbing or longer contact leads to more heating. This is different from dielectric heating, which comes from energy losses in insulating materials under alternating electric fields, and from resistance heating, which comes from electrical resistance in a conductor carrying current. Static electricity involves charge buildup with little to no heat produced. A practical example is rubbing hands together—the warmth comes from frictional heating.