What are three types of energy?
Mechanical energy, Electrical Energy, Thermal Energy
Mechanical energy may be further subdivided into potential energy, kinetic energy, spring energy.
Other forms of energy also exist such as sound energy, light energy. mass energy, nuclear energy, etc.
Very important to note is the Law of Conservation of Energy which states that energy cannot be created or destroyed, but can be converted between different forms.
So for example, an object at the top of a steep hill has E joules of gravitational potential energy. As it falls down it loses height but gains speed, heats up and makes a noise due friction, and at the bottom it has lost all its potential energy, but gained an equivalent amount of other forms so that the total of sound, heat and kinetic equals exactly E joules.