Work and power — Physical education, 14–17 years
Work measures energy transferred by a force; power measures how quickly that transfer happens.
Moving energy with a force
In physics, work is done when a force makes an object move in the force’s direction. More force or more distance means more energy transferred. Power is not the amount of work; it is the rate at which the work is done.
Why separate work from power?
Two machines can transfer the same energy but take different times. Saying only “how much work” hides that difference, which matters when comparing engines, lifts or athletes. Work answers “how much energy?”; power answers “how fast?”
Lifting a box
A person lifts a 20 kg box by 1.5 m. Using g = 10 N/kg, its weight is 20 × 10 = 200 N. Work = force × distance = 200 × 1.5 = 300 J. If the lift takes 5 s, power = work ÷ time = 300 ÷ 5 = 60 W.
The tiredness trap
Holding a heavy bag still feels tiring, so it is natural to say that physics work is being done. But if the bag does not move, the lifting force transfers no energy through distance, so the mechanical work on the bag is zero. Your muscles still use chemical energy internally.
Appliances and lifts
A kettle’s power rating tells you how quickly it transfers electrical energy into the water, not how much water it must heat in total. A lift motor needs enough power to raise people quickly, while its total work depends on their weight and the height reached.
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