The amount of energy in a system can be changed. It cannot be created or destroyed but it can be transferred, dissipated or stored in different ways.

The amount of gravitational potential energy stored by an object at height can be calculated using the equation:

change in gravitational potential energy = mass x gravitational field strength x change in vertical height

This is when:

- change in gravitational potential energy (
*ΔGPE*) is measured in joules (J) - mass (
*m*) is measured in kilograms (kg) - gravitational field strength (
*g*) is measured in newtons per kilogram (N/kg) - change in vertical height (
*Δh*) is measured in metres (m)

A 3.5 kg cat climbs a tree. The tree is 5.6 m high. How much gravitational potential energy has the cat gained? (g = 10 N/kg)

- Question
How much gravitational potential energy does a 500 g bag of flour gain when it is lifted up 1.5 m onto a shelf?

The amount of kinetic energy of a moving object can be calculated using the equation:

This is when:

- kinetic energy (
*KE*) is measured in joules (J) - mass (
*m*) is measured in kilograms (kg) - speed (
*v*) is measured in metres per second (m/s)

A dancer with a mass of 90 kg moves at a speed of 6 m/s across the stage. What is his kinetic energy?

- Question
How much kinetic energy does a 300 g kitten have when it runs at 4 m/s to chase a butterfly?

For any of these equations you may need to change the subject of the formula.