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 energy stored by an object at height can be calculated using the equation:
Gravitational potential energy = mass × gravitational field strength × height
This is when:
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? ( = 10 N/kg)
= 5 × 10 × 56
= 2,800 J
How much gravitational potential energy does a 500 g book gain when it is lifted up 1.5 m onto a shelf?
= 0.5 × 10 × 1.5
= 7.5 J
For any of these equations you may need to change the subject of the formula.