**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.