- Energy is defined as the capacity to do work.
- Work is done when energy is converted from one form to another.
- The unit of work is Nm or Joule(J)

Gravitational Potential Energy

Gravitational potential energy is the energy stored in an object as the result of its vertical position (i.e., height).

Formula:Gravitational potential energy is the energy stored in an object as the result of its vertical position (i.e., height).

**Example**:

A ball of 1kg mass is droppped from a height of 4m. What is the maximum kinetic energy possessed by the ball before it reached the ground?

**Answer**:

According to the principle of conservation of energy, the amount of potential energy losses is equal to the amount of kinetic energy gain.

Maximum kinetic energy

= Maximum potentila energy losses

= mgh = (1)(10)(4) = 40J

Elastic Potential Energy

Elastic potential energy is the energy stored in elastic materials as the result of their stretching or compressing.

Formula:Elastic potential energy is the energy stored in elastic materials as the result of their stretching or compressing.

**Example**:

Diagram above shows a spring with a load of mass 0.5kg. The extention of the spring is 6cm, find the energy stored in the spring.

**Answer**:

The energy stored in the spring is the elestic potential energy.

$$\begin{array}{l}{E}_{p}=\frac{1}{2}Fx\\ {E}_{p}=\frac{1}{2}(5)(0.06)=0.15J\end{array}$$