STARTER:

• List the different types of POTENTIAL energy

• What does the word POTENTIAL in this context mean?

• Can you give some examples of potential energy being transferred to a different type of energy?

When a bungee jumper starts to fall he starts to lose GPE.

As the elastic cord pulls the bungee jumper back up, he gains GPE.

The gravitational potential energy (GPE) of an object on Earth depends on its mass and its height above the Earth’s surface.

What is gravitational potential energy?

Chemical kinetic gravitational

Gain in GPE = work done = m x g x h

Work = mass x g x height

How is GPE calculated?The GPE of an object can be calculated using this equation:

GPE = mass x gravitational field strength x height

Height is measured in metres (m).

Mass is measured in kilograms (kg).

GPE is measured in joules (j).

Gravitational field strength is measured in newtons per kilogram (N/kg), usually taken as 10 N/kg on Earth.

Example

A dog of mass 12 kg falls from an aeroplane at a height of 3.4 km. How much gravitational energy does the dog have as it leaves the aeroplane?

Woof! (help!)

ExampleOn earth g = 10 m/s2

Height = 3.4 km = 3400 m

Mass of dog = 12 kg

ExampleOn earth g = 10 m/s2

Height = 3.4 km = 3400 m

Mass of dog = 12 kg

GPE of dog = mgh = 12kg x 10m/s2 x 3400m = 408 000 J

Example

GPE of dog = mgh = 12kg x 10m/s2x 3400m = 408 000 J

Just before the dog hits the ground, what has this

GPE turned into?

Kinetic energy

An osprey with a mass of2 kg flies at a height of200 m above the ground.

Calculating GPE Group question

How much gravitational potential energy does the osprey have?

= 2kg x 10 m/s2 x 200m

GPE = mass x gravitational field strength x height

= 4,000 J

I´m big, Scottish

and I like fish

An apple with a mass of 200

g falls 3 m from its branch to the ground.

Calculating GPE Group Question

How much GPE will the apple have lost when it reaches the ground?

= 0.2kg x 10m/s2 x 3m

= 6 J

= mass x gravitational field strength xGPElost

changein height

Newton stole my

idea

Time to try it for ourselves!

• Collect data using the method detailed on your worksheet

• Write a conclusion for your experiment

Extension 

Calculate the g.p.e. gained by Olaf of mass 55kg when he climbs up stairs of height 3m.

Calculate the mass of Sven if she gains 400J of g.p.e. when she climbs up stairs of height 4m.

Calculate the height gained by Inge, of mass 50kg, if he gains 2500J of g.p.e.

Calculate the g.p.e. gained by a fly of weight 0.05N when it climbs up a height of 200mm.

Calculate the gravitational field strength in a place when Orla of mass 20kg gains 100J of g.p.e when climbing up a height of 3m.

Energy transfer of falling objects

What happens to the kinetic energy (KE) and GPE of a rollercoaster?

The law of conservation of energy means that as an object falls, the GPE it loses must turn into a different form.

This is only true if air resistance and friction are ignored.

GPE lost = KE gained

The relationship between GPE and KE

In reality, GPE would also be transferred into heat and sound energy so the KE of rollercoaster would be less than the GPE lost.