A system is an object or a group of objects.
Energy is what makes things happen or change.
Energy stores are where objects keep energy.
There are eight main types of energy stores: thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, nuclear.
Thermal energy is the energy stored in an object from the movement of the particles that the object is made of.
Kinetic energy is the energy stored in an object because it is moving.
Gravitational potential energy is the energy stored in an object from the gravitational force pulling the object towards the Earth.
Elastic potential energy is energy stored in an object when it is stretched out or compressed.
Chemical energy is energy stored in an object’s chemical bonds.
Magnetic energy is energy stored when two magnets, or a magnet and a magnetic material, are attracted or repelled.
Electrostatic force is the energy stored when charged objects are attracted or repelled.
Nuclear energy is the energy stored inside the nucleus of an atom and released during nuclear reactions.

The total energy of the system is the sum of all the energy in all the energy stores in the system.
Net energy is the change in the total energy of a system.
Net energy can be calculated as the energy transferred into the system, minus the energy transferred out of the system.
The unit of energy is joules (J).
Closed systems are systems where no energy or objects can enter or leave the system.
The total energy of a closed system is always the same.
The net energy of a closed system is always zero as no energy can enter or leave the system.

When a system changes, energy is always transferred.
The movement of energy from one energy store to another is called an energy transfer.
Energy can be transferred in two ways, by doing work or by heating.
Work done means energy transferred.
There are two ways work can be done, by a force being exerted or by an electrical current flowing.
Heating is the energy transfer from one object’s thermal energy stores to another object’s thermal energy stores.

When a person throws a ball up, the force exerted by the person on the ball does work. Energy is transferred from the person’s chemical energy stores to the ball’s kinetic energy stores.
When a ball falls down, the gravitational force does work on the ball. Energy is transferred from the ball’s gravitational potential energy stores to its kinetic energy stores.
When an electric kettle brings water to a boil, heating takes place. Energy is transferred from the kettle’s heater's thermal energy store, to the water’s thermal energy.
When car brakes are pressed, friction between the car’s brakes and the wheels of the car exerts a force that does work. Energy is transferred from the wheels’ kinetic energy stores to the thermal energy stores of the surroundings.
When a cyclist hits a fence the normal contact force between the cyclist and the fence does work. Energy is transferred from the cyclist’s kinetic energy stores to other types of energy stores in the fence and surroundings.

Module Review