What effect does friction have on the motion of a moving object?

• A. Increases speed
• B. Has no effect
• C. Changes direction
• D. Opposes motion and converts kinetic energy to thermal energy

Answer: (D)

Friction acts as a resistive force between surfaces in contact when something is moving. It points opposite to the direction of motion, so it slows the object down. The energy the moving object loses as kinetic energy is turned into heat in the surfaces, which is why brakes warm up when you stop. Friction doesn’t make things go faster, and it doesn’t do nothing to moving objects. It also doesn’t typically make a moving object change direction by itself; it mainly slows motion and converts energy to heat.