Calculating and comparing gravitational potential energies

Calculation method

To calculate Epp, simply apply the formula Epp = m * g * h, provided that International System units are used: kg for mass, m for height, and N/kg for g. The result is then expressed directly in joules.

Numerical example with table

Let us compare the gravitational potential energy of several objects, taking the ground as the reference point (g = 10 N/kg):

Object	Mass (kg)	Height (m)	Epp (J)
Ball	0.2	2	4
Rucksack	8	1.2	96
Skier	70	50	35,000

We can see that Epp increases in proportion to both mass and height: doubling either one doubles Epp.

Be careful with units

If mass is given in grams or height in centimetres, you must convert them before calculating: m to kg (divide by 1,000), h to m (divide by 100). Forgetting to do this conversion is the most common mistake.

Special case: h = 0 or negative h

If the object is at the reference level, Epp = 0. If the object is below the reference level (for example, at the bottom of a well, with the reference at ground level), h is negative and Epp is negative: this remains physically consistent, as only the change in energy really matters.