Whenever an object is moving, it has energy in its kinetic energy store. The amount of kinetic energy depends on the mass and velocity of the object.

You can calculate the amount of energy in an object's kinetic energy store ($Ek$) using the following formula:

• $m$ = the mass of the object in kilograms (kg)
• $v$ = the velocity of the object in metres per second (m/s).

When an object is lifted in a gravitational field, it gains energy in its gravitational potential energy store. The amount of gravitational potential energy depends on the mass of the object, how high it has been lifted and the strength of the gravitational field. On Earth, the gravitational field strength is approximately 9.8 m/s

The amount of energy in the gravitational potential energy store ($Ep$) can be calculated using the following formula:

• $m$ = the mass of the object in kilograms (kg)
• $g$ = the gravitational field strength in newtons per kilogram (N/kg)
• $h$ = the change in the height of the object in metres (m). You may have to calculate the height the object has been lifted by subtracting the starting height from the final height.

When an object is stretched or squashed, it gains energy in its elastic potential store. The amount of elastic potential energy depends on the extension (distance the object is stretched or squashed) and the spring constant of an object. The spring constant is individual to each object and is measured in Newtons per metre (N/m).

The amount of elastic potential energy ($Ee$) stored in an object can be calculated using the following formula:

• $k$ = the spring constant of the object measured in newtons per metre (N/m)
• $x$ = the extension (or compression) of the object in metres (m). This is shown on the diagram on the right. You may have to calculate the extension of the object by subtracting the final length from the starting length.