// physics › Energy
Find the gravitational potential energy of a raised body from its mass and height, or solve for mass or height.
PE = m g h
It is stored-up energy that something has because of how high it is. Lift a ball onto a shelf and it now holds energy, just waiting. Let it go and that stored energy turns into movement as it falls. The higher you lift it, the more it stores. 'Potential' just means 'ready and waiting'.
Because gravity is always pulling things down. When you lift something up, you are working against that pull, and that effort gets stored in the object. The object is now in a position to fall, and falling releases the energy. No height, nothing stored — a ball on the floor has no room to fall.
That is the strength of Earth's gravity. It tells us that everything speeds up by about 9.81 metres per second, every second, as it falls. We use 9.81 as the standard number. On the Moon it would be much smaller, which is why astronauts bounce around so easily.
Of course. Lift a 2 kg book up to a 5 m high shelf. The formula is PE = mass × g × height. Step 1: mass × g = 2 × 9.81 = 19.62. Step 2: multiply by the height: 19.62 × 5 = 98.1. So the book stores 98.1 joules of potential energy. A joule (J) is just the unit for energy.
From whatever level you call 'the bottom' — usually the floor or a table. Height is always measured from a starting line you choose. Just be consistent: if you start counting from the floor, keep using the floor.
A roller-coaster car at the top of the first hill is packed with potential energy — that is why the drop is so thrilling as it turns into speed. Water held high behind a dam, a drawn bow, a ball at the top of a ramp: all storing energy, ready to be released.