Energy stores and transfers
Identify kinetic, gravitational potential, elastic potential, thermal, chemical, nuclear, magnetic and electrostatic energy stores. Describe transfers mechanically, electrically, by heating and by radiation, distinguishing stores from transfer pathways.
What a learner can do afterwards
- Names and describes at least five energy stores with a real-world example of each
- Identifies the energy stores at the start and end of a given process (e.g. a falling ball, a burning match)
- Describes the transfer pathway connecting two energy stores in a given scenario
- Traces energy through a system identifying all stores and transfers involved
1 · Read
An energy store describes energy held in an object or system. Kinetic energy is linked to motion. Elastic potential energy is stored by stretching or compressing something. Thermal energy includes energy linked to particle motion inside matter. Heating the same sample without a change of state increases its thermal store and temperature. Cool matter also has a thermal store.
Food, fuel and batteries have chemical stores. Respiration releases energy from food; burning releases energy from fuel. Nuclear stores involve atomic nuclei. Magnetic and electrostatic stores depend on positions of magnets and charges. When an object descends and speeds up, its system's gravitational potential store decreases and its kinetic store increases. Light carries energy by radiation; it is not an energy store in this model.
Energy is transferred mechanically when a force does work, such as pushing a trolley or stretching a spring. It is transferred electrically in a circuit. Heating transfers energy from warmer to cooler matter. Radiation, including visible light and infrared, can transfer energy through empty space. Name both the stores and the pathway connecting them.
A torch's battery chemical store decreases. Energy is transferred electrically to the lamp. The lamp warms, increasing its thermal store, and emits light by radiation. When the light is absorbed by a wall, the wall's thermal store increases. These are different destinations, not a single chain through a light store.
Sunlight reaches Earth by radiation across space. When the ground absorbs it, the ground's thermal store can increase. A burning match also transfers energy to nearby matter by heating and emits radiation. Its chemical store decreases; thermal stores in the match and surroundings increase. Light leaving the match is a transfer, not an electromagnetic store.
Winding a toy car deforms its spring and increases the elastic potential store. Releasing it lets the spring do work, increasing the car's kinetic store. As the car slows, friction transfers energy mechanically into thermal stores in the car and floor. The stores change, but energy has not disappeared.
Energy never disappears. It just moves from store to store along a pathway: mechanically, electrically, by heating, or by radiation.
Original readings about energy stores and transfer pathways written for this learning collection.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.