Hi and welcome back to freesciencelessons.co.uk. By the end of this video you should be able to calculate the amount of gravitational potential energy gained by an object raised above ground level. So we're going to start by looking at what's meant by gravitational potential energy. Gravitational potential energy is the energy stored in an object due to its position above the Earth's surface. and this is due to the force of gravity acting on an object.
We're going to start by looking at a simple example. This shows a ball sitting on the ground. I'm now going to lift the ball off the ground and place it on a shelf like this.
To do this I'm using the chemical energy stored in my muscles and I'm changing this to gravitational potential energy in the ball. So the ball now has a store of gravitational potential energy. If I now allow the ball to fall off the shelf back to the ground like this, then the store of gravitational potential energy is now changed to other forms of energy, such as thermal energy and kinetic energy. So the ball now has no gravitational potential energy.
We can calculate the gravitational potential energy of an object by using this equation. The gravitational potential energy in joules equals the mass in kilograms multiplied by the gravitational field strength multiplied by the height in meters. The gravitational field strength is a measure of the force of gravity and this value will be given in the question. Now you are not given the equation for gravitational potential energy in the exam.
You've got to make sure that you learn it. Okay, let's take a look at a sample question. A crane lifts a 75 kilogram mass a height of 8 meters.
Calculate the gravitational potential energy gained by the mass. The value of the gravitational field strength is 9.8 newtons per kilogram. So, here's the equation that we're going to use. The mass of the object is 75 kilograms.
The gravitational field strength is 9.8 newtons per kilogram and the height is 8 meters. Putting these numbers into the equation gives us a gravitational potential energy of 5880 joules. Here's a question for you to try.
A ball with a mass of 500 grams is lifted onto a shelf which is 1.5 meters above the ground. calculate the gravitational potential energy gained by the ball. Pause the video now and try this yourself.
Okay, here's the equation that we're using. The mass is 500 grams, so first we've got to convert this to kilograms by dividing by 1000. 500 grams is 0.5 kilograms. The value of the gravitational field strength is 9.8 newtons per kilogram and the height is 1.5 meters. Putting these numbers into the equation gives us a value for the gravitational potential energy of 7.35 Joules.
Remember you'll find plenty more questions on gravitational potential energy in my revision workbook, and you can get that by clicking on the link above. Okay, so hopefully now you should be able to calculate the amount of gravitational potential energy gained by an object raised above ground level.