An object that is lifted from the ground gains energy since it can go on to do something else. A glass on the floor stays stable, one on a table can drop and smash.
The amount of gravitational potential energyThe energy stored by an object lifted up against the force of gravity. Also known as GPE. stored by an object at height can be calculated using the equation:
Gravitational potential energy = mass × gravitational field strength × height
\(\text{E}_{p} = \text{mgh}\)
This is when:
gravitational potential energy (\(\text{E}_{p}\)) is measured in joules (J)
mass (\(\text{m}\)) is measured in kilograms (kg)
gravitational field strength (\(\text{g}\)) is measured in newtons per kilogram (N/kg)
height (\(\text{h}\)) is measured in metres (m)
Learn more on kinetic and gravitational potential energy in this podcast
A 5 kg object is taken to the top of a building. The building is 56 m high. How much gravitational potential energy has the object gained? (\(\text{g}\) = 10 N/kg)
\(\text{E}_{p} = \text{mgh}\)
\(\text{E}_{p}\) = 5 × 10 × 56
\(\text{E}_{p}\) = 2,800 J
Question
How much gravitational potential energy does a 500 g book gain when it is lifted up 1.5 m onto a shelf?
\(\text{E}_{p} = \text{mgh}\)
\(\text{E}_{p}\) = 0.5 × 10 × 1.5
\(\text{E}_{p}\) = 7.5 J
For any of these equations you may need to change the subject of the formula.
