A system is an object or a group of objects. When a system changes, energy is transferred between the ways it is stored. These ways are called energy stores: kinetic, gravitational potential, elastic potential, thermal, chemical, magnetic, electrostatic and nuclear.
Energy moves between stores by work done by a force, by work done when an electric current flows, or by heating. You should be able to describe the changes for common situations:
- An object thrown upwards: energy moves from its kinetic store to its gravitational potential store as it rises.
- A moving object hitting an obstacle: energy moves from its kinetic store to the thermal store of the object and the obstacle.
- An object accelerated by a constant force: the work done by the force transfers energy to the object's kinetic store.
- A vehicle slowing down: energy moves from its kinetic store to the thermal store of the brakes.
- An electric kettle: work done by the electric current transfers energy to the thermal store of the water, which rises in temperature until it boils.
