now energy is a bit like money and it can be stored in different places or maybe transferred from one store to the other or we can also think of it a bit like a liquid that's may be transferred from different store to different store now there are a number of different stores that we need to consider so we have kinetic energy which is due to how quickly things are moving we've got a lastly potential if you maybe deform an object like you squash it or squeeze it gravitational potential is to do with how high you move something and then we've got thermal which is the internal energy store as well as a few others now what we can do is with energy we actually work things out and if we wanted to work out the kinetic energy for example the kinetic energy is equal to 1/2 MV squared where the V here stands for the speed of the object and that's measured in meters per second we should always measure our mass in kilograms and then this means that the unit for energy is the Joule this energy is equal to 1/2 ke squared where e is the extension of that object not how long it is completely but how much longer it has become and again what we do we measure our extension in meters K is the spring stiffness and this is measured in Newtons per meter and once again we measure our energy in joules our gravitational potential energy EP is equal to mg H so here again we have our energy in joules our mass in kilograms H is the height that something moves through in meters and G is what we call the gravitational field strength and on earth this has a value of 9.8 Newton's per kilogram but this does depend on where you are in the universe some things like the moon for example have a much smaller value of their gravitational field strength when it comes to looking at thermal energy what we can do is we can change the thermal energy of something by looking at MC delta theta so here what we have is our theta that's our temperature and that's measured in degrees Celsius we measure our mass in kilograms and this thing down here little C is our specific heat capacity and this is the amount of energy required to raise the temperature of one kilogram of something of the substance by one degrees Celsius so that means a unit for this are joules per kilogram per degree Celsius so we have these different stores of energy but what we can now consider is the different ways that energy is transferred from one store to the other and there are four main transfers that we need to think about so these are our four transfer processes you've got heating electrical working radiation and this could be things like sound waves or it could be light waves and also the rest of the parts of the electromagnetic spectrum and finally we have mechanical now what it's really important to look at the way that energy is transferred from one store to the other and what we might consider is at the start of a process we can maybe consider the energy store we then need to define a clear end point and we can consider how the energy stored at this point and what we can then do is think about the transfer as well so these are some of the things we need to think about if you've got an object projected upwards maybe it starts as the kinetic energy store and ends up transferred to the gravitational potential store if you've got a moving object hitting an obstacle it might end up going from the kinetic store radiated by sound perhaps into the thermal store the surroundings if you've got something which is accelerating depending on what provides his force you might then increase the kinetic energy store you've got to be familiar with all of these and get used to doing different problems where you might have different energy stores and that just comes with practice it's also worth considering how quickly that transfer takes place and what we can then think about is the idea of power so power is defined as the rate at which energy is transferred or at which work is done now that we can say that power is equal to the energy transferred divided by time and the word rate just means the amount per second or we can also look at power as the work done per unit time and we always measure energy and work done in joules if we measure time in seconds this then gives us a power measured in the watt now when we think about an energy transfer process although some of the energy might be transferred to a useful store at the end some of the energy might also be wasted perhaps it's going to heat up the surroundings and what we can then think about is something called efficiency and efficiency is often given a number between zero and one or between zero and a hundred percent and we can work out the efficiency by looking at the useful output energy transfer divided by the total input energy transfer effectively the more energy that's transferred usefully the higher the efficiency and we can do the same thing where we're maybe not thinking about the energy transfer but the power and we can look at the useful power output compared to the useful the total power input and finally we can think about energy resources and what we're talking here is about things as to maybe use for transport for example cars we might think about electrical electricity generation and finally we can also use these for heating our homes and businesses what we could then need to do is think about maybe different ways in which we can generate electricity there are two main categories we've got non-renewable and renewable non-renewable resources once they're used up we can't replenish them so we're thinking about coal oil and gas as well as nuclear fuels and when we talk about nuclear fuel we often thinking about uranium or plutonium when it comes to innumerable energy resources so we have biofuel which can be burnt and the reason we burn all of these or year sister generate heat is to boil water water turns a turbine which then turns a generator which generates electricity one way we can get away with not burning things is to use wind turbines where it's a power of the wind directly which is causing the generator in the top of this to turn we can use solar cells which turn that sunlight into electricity we also have geothermal hydro wave and tidal where these are just different ways of having moving water hitting a turbine to call the generator to turn so that is energy for a QA you