Conservation of energy — Physical education, 14–17 years
Energy can move between objects and change form, but it is not simply destroyed. Tracking the transfers explains machines, falls, heating, and many everyday changes.
Energy changes form
Energy is a way of tracking the ability to cause change. It can be stored in height, motion, stretched materials, fuel, or electrical systems, then transferred or transformed. In every process, the total amount is conserved, although some may spread into the surroundings as thermal energy.
Why follow energy?
Machines rarely produce useful effects without transfers: a motor needs an input, and a lamp changes electrical energy into light and heat. The conservation idea arose because scientists needed a reliable account of what happened in engines, collisions, and heating experiments. It prevents us from inventing energy that was never supplied.
A falling ball
A 2 kg ball is held 5 m above the ground. Using gravitational energy mgh, with g ≈ 10 N/kg, it starts with 2 × 10 × 5 = 100 J of gravitational energy. Just before impact, ignoring air resistance, this has become about 100 J of kinetic energy. The energy changed form; it did not vanish.
“Wasted” energy
It is tempting to say that energy is lost when a machine becomes warm or makes noise. That is reasonable because the intended useful output is smaller, but the energy has usually been transferred into heating, sound, or movement of the surroundings. “Wasted” means less useful for us, not destroyed.
Making technology efficient
Engineers use energy accounts to improve cars, heaters, solar panels, and power stations. They ask where the input energy goes and how much becomes the intended output. Better insulation reduces heating transfers to the surroundings, while regenerative braking sends some car motion back into the battery.
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