Energy Stores and Systems

Energy is never used up, instead it is transferred between different energy stores and different objects.

Energy is Transferred between stores

When energy is transferred to an object, the energy is stored in one of the object’s energy stores.

There are eight energy stores:

1. Thermal energy stores
2. Kinetic energy stores
3. Gravitational potential energy stores
4. Elastic potential energy stores
5. Chemical energy stores
6. Magnetic energy stores
7. Electrostatic energy stores
8. Nuclear energy stores

Energy is transferred mechanically(by a force doing work, electrically(work done by moving charges), by heating or by radiation(e.g. light or sound)

When a System Changes, Energy is Transferred

1. A system is just a fancy word for a single object or a group of objects that you are interested in.
2. When a system changes, energy is transferred. It can be transferred into or away from the system, between different objects in the system or between different types of energy stores.
3. Closed systems are systems where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero.

Energy can be transferred by heating

1. Take the example of boiling water in a kettle - you can think of the water as the system. Energy is transferred to the water(from the kettle’s heating element) by heating, into the water’s thermal energy stores(causing the temperature of the water to rise).
2. You could also think of the kettle’s heating element and the water together as a two-object system. Energy is transferred electrically to the thermal energy store of the kettle’s heating element which transfers energy by heating to the water’s thermal energy store.

Energy can also be transferred by doing work

Work done is just another way of saying energy transferred. Work can be done when current flows(against resistance in a circuit) or by a force moving an object.