Which term best completes the sentence: Gear transmit _______ between machines while changing rotation, speed, and torque.

• A. Power
• B. Energy
• C. Momentum
• D. Force

Answer: (A)

Power is the rate at which energy is transferred, and gears are designed to move mechanical power from one shaft to another while changing rotation speed and torque through the gear ratio. The relationship P = τ · ω shows why this happens: if speed rises, torque falls proportionally (and vice versa) so the transmitted power remains roughly constant aside from losses. Energy describes total work available, not the ongoing rate of transfer, and momentum or force describe different quantities (orbiting around how fast something is rotating or the instantaneous contact force), not the continuous transfer of energy itself. So the term that best fits the sentence is power.