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What is gravitational potential energy?
Any object that is off the ground has the potential to fall down. Think of a roller coaster at the top of a loop - it is all part of the thrill to be taken up to a great height, and then accelerated back down again.
Gravity wants to pull everything down to Earth, so we say that objects that are off the ground are storing gravitational potential energy (GPE). The more massive an object is, and the higher it is from the ground, the more GPE it stores.
How is it calculated?
The equation for gravitational potential energy is:
GPE = m g h
Where GPE = gravitational potential energy, m = mass, g = gravitational field strength (which is always 9.81 N/kg on Earth), and h = height.
As GPE is a form of energy, its units are Joules. The equation only works if mass is in kilograms and height is in metres.
If we want to calculate how much gravitational potential energy an object has, we just multiply the three numbers together.
Let's do a quick example:
A child holds a 2 kg ball, 1.5 m off the ground. To calculate the ball's gravitational potential energy, we do the following calculation:
GPE = m g h
GPE = 2 x 9.81 x 1.5
GPE = 29.43 J
The principle of conservation of energy will always apply. If the child then drops the ball to the ground, it would transfer 29.43 J of energy in the process.
Now see if you can apply this equation in the questions in this activity.
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