An object will have potential energy due to its position relative to a zero point. This could be in a gravitational field (gravitational potential energy) or due to a stretched spring (elastic potential energy). This may be a little harder to understand than kinetic energy initially due to the spring constant and gravitational field strength, but don’t worry!
Gravitational potential energy
Gravitational potential energy in Joules
Mass in kilograms
Gravitational field strength in Newtons per kilogram
Height in metres
Any object on Earth that is raised above the ground does work against gravity and therefore gains potential energy. The amount of energy depends on the mass of the object and the height above ground. In the below example, the bird on the bottom wire has less potential energy than the bird with the same mass above it, and in turn the bird with greater mass will have greater potential energy than the other bird on it’s wire.
For example:
The top wire is at a height of 10m, the smaller bird has a mass of 900g and the large bird has a mass of 1.5kg, what is the difference in their gravitational potential energy (gravitational field strength on Earth = 9.8 N/kg)? Look out for SI units!
Potential Energy of small bird = 0.9 kg x 9.8 N/kg x 10 m = 88.2 J
Potential Energy of large bird = 1.5 kg x 9.8 N/kg x 10 m = 147 J
Difference in potential energy = 147 - 88.2 = 58.8 Joules
Elastic potential energy
Ee = ½ k e2
Potential energy in Joules
The spring constant in Newtons per metre
Extension in metres
The spring constant, denoted by k, is derived from Hooke's Law