Lesson 15.1 notes
Energy stores, the four ways energy is transferred, conservation of energy, and wasted energy.
Energy is kept in energy stores, such as kinetic (moving things), gravitational (raised things), elastic (stretched or squashed things), chemical (food, fuels, batteries) and thermal (hot things).
Energy is transferred between stores in four ways: by forces (mechanically), by an electric current, by heating, and by waves such as light and sound.
As a ball falls, its gravitational store empties and its kinetic store fills. When it lands, the energy is transferred by heating and sound, ending up in the thermal store of the surroundings.
Energy can't be created or destroyed, only transferred. This is the law of conservation of energy: the total energy is the same before and after any change.
An energy transfer diagram shows where the energy goes, with arrow widths showing amounts. Of every 100 J a filament bulb takes in, only about 10 J comes out as light.
Wasted energy is dissipated: it spreads out into the surroundings, usually warming them a little. Once it is that spread out, it can't do anything useful.
Stretching a spring moves energy from your muscles' chemical store to the spring's elastic store. Burning fuel and lighting a lamp move energy from chemical stores to thermal stores.
Choose something that happens and move through it. Watch the energy stores change while the total stays the same.
When a battery goes flat, its energy hasn't vanished. It has been transferred, mostly to the thermal store of the surroundings. Energy is never used up; it ends up so spread out that it is no longer useful.
GCSE: Energy stores and transfers → GCSE: Conservation of energy → GCSE: Efficiency →