Hi, I'm Donald Sinclair. I'm a science teacher with Greater London Tutors and today, we are going to look at a few in chemistry. These are how to do calculations involving potential energy. The gravitational potential energy are measurements of about how much work you have to do against the force of the weight caused by gravity. A quick review of our work done is the work done is simply the force against which you are doing the work multiplied by the distance over which something is moved. So,for example, if you are pushing a box with a resistive force of twenty newtons over a distance of two meters, the work done would simply be twenty times two equals forty joules. A very common force in on which you are familiar with is weight which is caused by gravity and so there is great deal of examples where you have to work on how the work done against more commonly expressed gravitational potential energy. Consider for example, a crane lifting a five hundred kilogram mass, up a height of sixteen meters. If we are to use this equation here, you would have work done equals a force against which the crane is working, which in this case, is a weight of mass. So, would be the mass times the acceleration due to gravity g and then multiplied by the distance, which we can call a height in this case to be moving up and down, that the crane is to be moved. And this is more commonly given a different symbol. I'm going to use EP and E for energy, P for potential energy, gravitational potential energy in this case. So for this example, the mass five hundred multiplied by the acceleration due to gravity, which I am going to use the simple value ten here, if you ought to be more precise, it's nine point eight one, this keeps the sums easier multiplied by the height over which it is moved. This gives us a total of eighty thousand joules and now this is a gain in energy, this is not if we have had zero joule to start and eight thousand in the end. It simply means that after it has been raised this height been given an extra eighty thousand joules. If we have something falling for example, a fifty kilograms skydiver falling out of a plane, falling a height of eighteen hundred meters, there will be a loss of potential energy. In this case, potential energy equals the mass of the skydiver times gravity times height of eighteen hundred meters, which will give us a total energy loss, in this case of nine hundred thousand joules. So something being raised up gains potential energy, something falling losses potential energy. Remember that the g is measure of gravitational field strength and it depends on which planet you are on. You don't only use nine point eight one newtons per kilograms of here on Earth, on the Moon, it would be one point six. For example, see it would be weighed less. When in Jupiter, it would be twenty-seven, seems to weigh more. Make sure you use the right value in your calculations. And that's how you do these simple calculations involving potential energy. .