Physics · Chapter 04
⚡ Work, Energy & Power
Energy never lost, only changed.
💡 Energy Never Disappears
Work is done when a force moves an object: W = F × d. Push a box 5 m with 10 N → you did 50 joules of work.
Energy is the ability to do work. It comes in many forms — but it's never created or destroyed, only transformed.
A ball at the top of a hill has potential energy (stored, ready to fall). As it rolls down, that becomes kinetic energy (motion energy).
KE = ½ × m × v²
Power is how fast you do work: P = W ÷ t. A strong worker lifts the same load faster — more power.
Hydroelectric dam — potential energy of water converted to electrical energyWikimedia Commons / CC BY-SA 3.0
Solar panels — photovoltaic conversion of solar energy to electricityWikimedia Commons / CC BY-SA 3.0
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The Roller Coaster of Energy
AnimationWatch energy convert: high up = potential. Rolling down = kinetic. Total stays constant.
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Calculate Kinetic Energy
ExperimentChange mass and speed. See how KE grows — doubling speed gives 4× the energy (because of v²).
10 kg
5 m/s
KE = ½ × m × v²125 J
A 10 kg object moving at 5 m/s carries 125 joules of energy.