Gravitational Potential Energy

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Gravitational Potential Energy

Gravitational potential energy (GPE) is a type of stored energy.

If flower pots fall out of a tall building, one from the ground floor window and one from the fourth floor window. Which plant would be more likely to survive after it has hit the ground?

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The higher up an object is the greater its gravitational potential energy. The larger the distance something falls through the greater the amount of GPE the object loses as it falls. As most of this GPE gets changed into kinetic energy, the higher up the object starts from the faster it will be falling when it hits the ground.

So a change in gravitational potential energy depends on the height an object moves through.

Lifting an apple up 1 metre is easier work than lifting an apple tree the same height. This is because a tree has more mass, so it needs to be given more gravitational potential energy to reach the same height.

So a change in gravitational potential energy also depends on the mass of the object that is changing height.

Put the following pictures in order, starting with the object that you think will have the most GPE.

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The amount of gravitational potential energy can be found using:

Change in G.P.E.= mass x gravity x change in height

Gravitational potential energy is measured in joules, J.

Gravity is measured in newtons per kilogram, N/kg (or metres per second squared m/s2)

Height is measured in metres, m. (Not cm!!)

Note: The formula above is the same as:

Work done (or energy) = Force x distance

Where force is the weight of the object changing height. Weight is calculated using:

weight = mass x gravity

And the distance is the change in height. 

Here's one to try!

In the example below, a car rolls down a frictionless slope.

How much gravitational potential energy does it lose by the time it reaches the bottom?

Enter the correct values in the boxes below:

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If your answer was incorrect, did you remember to use the right distance. Remember the force and distance must be in the same direction. Weight is downwards, so you must use the distance downwards, not the distance along the slope!

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