Conservation of Energy

For the purposes of this course we will define energy to be the ability to make a change during an interaction. You may like to think of objects in a system as either energy sources or energy receivers. During an interaction the energy sources cause the change and the energy receivers are changed.

The idea of energy sources and receivers implies a conservation law. In a closed system the total amount of energy does not change. However, energy within the system can change form. This differs from the concepts of conservation of momentum and charge which don't change form.

Example of energy changing form
List at least two ways in which you can give an object some energy.

Different forms of energy:
Potential Energy - the potential to make a change, e.g. attraction or repulsion of magnets.

Example of kinetic energy
A neutron and a proton have the same mass. Suppose a neutron is moving twice as fast as the proton. How much greater is the neutron's kinetic energy?

If a system is closed then the total kinetic energy + potential energy remains a constant.

Other forms of energy include:
· Electrical
· Chemical
· Thermal
· Elastic
· Mass-Nuclear
· Light and other electromagnetic radiation
· Sound
· Gravitational

Energy in a closed system is always conserved, so in an interaction we need to consider all forms of energy to ensure energy has not appeared or disappeared.