Gravitational potential energy E =mgh We can store energy and release it in different forms. Stored energy is commonly referred to as potential energy. There are many forms of potential energy, elastic, chemical and gravitational are but a few. Things that are high up off the ground are said to have gravitational potential energy. They have the ability to do work. The higher they are, the more work they can do for us, on the way down, therefore the more energy they have stored. Gravitational potential energy is calculated by the formula E =mgh (m is the mass of the object in kilograms, g is a constant related to Earth’s gravitational force accelerating objects towards its centre at 9.8 m/s/s and h is the height of the object in metres. A 267.5kg weight is lifted by a weightlifter 2.1 metres high off the floor. Calculate the gravitational potential energy of the bar at its hieghest point. E=mgh = 267.5 X 9.8 X 2.1 = 5510 Joules of energy. An 80kg firefighter is trapped on top of a burning building. His colleagues, on the ground, suggest he jump onto a blue safety-mat placed at the base of the building. Calculate the firefighter's gravitational potential energy if the top of the building is 200m high. E = mgh = 80 X 9.8 X 200 = 156800j = 156.8 kilojoules. Exercises