energy isn't something you can hold in your hand it's just an idea it's a number that tells us what will happen when objects interact in what we call a system total energy in any interaction is always conserved energy cannot be created or destroyed now there is a small caveat with that as energy can be turned into matter Mass but it's still technically true the whole Mass to energy thing is only important for triple people in topic four when it comes to nuclear fision and fusion there are what some people call different stores of energy normal people just say types of energy but these days the exam boards are obsessed with the word stores so that's what we're going to have to use the energy in these energy stores changes when objects interact energy is measured in Jewels an object can have energy in the following stores kinetic energy we calculate it with e = half mv^ 2 half * mass in kilog time speed or velocity squared the faster an object goes the more kinetic energy it has gravitational potential energy or GP for short we calculate that by eal MGH that's mass time gravitational field strength either 10 or 9.8 in Newtons per kilogram you'll be given it in any question that involves it Times by height in meters technically this only gives you a change in gpe as the H here should really be change in height the higher off the ground on object is the more gpe it has or rather the more gpe it has available to lose if it falls to the ground ground elastic potential energy is what we find in say a spring this is given by eal half k^2 that's half times the spring constant in Newtons per meter sometimes called stiffness times extension in me squar that's how much further the spring has stretched from its original length thermal energy or change in thermal energy is calculated with the shc equation energy equals mass time shc * temperature change in De C in simple form that's e equal MC delta T that Delta Ro triangle just means change in that's change in temperature here shc is short for specific heat capacity this tells you how much energy is needed to raise 1 kilogram of a substance by 1° celsus it's different for every material out there remember that an increase in thermal energy results in particles moving faster so this is essentially a way of measuring the kinetic energy gained by particles in a substance more on this in the particles topic we don't really talk about sound or vibrational energy as this is just particles moving so in reality it's kinetic again chemical potential energy say in food or fuels there's no equation for that and that's more chemistry's remit but you might have to mention at some point that these two things do have a store of chemical potential energy in order for anything to happen in a system energy must be transferred from one object to another or one store to another store in a closed system no energy is lost to the surrounding ings no energy in from the surroundings either which allows us to equate two lots of energy that just means saying that two lots of energy are the same for example a roller coaster car teetering at the top of a ride just has gpe gravitational potential energy basically zero kinetic energy as it starts to roll down gpe is turned into K okay I should probably say that it GP store is decreasing while it's K store is increasing instead but all that really matters is that at the bottom it's lost that gpe using this height here so we can say gpe lost equals ke gained gpe equals K so if it had this many jewels of gpe at the top it must have the same number of jewels of K at the bottom we can then rearrange the K equation to find its speed for example I always recommend rearranging equations using symbols not words so here I want to make V the subject leave it by itself so to move something from one side of an equation to the other we just do the opposite with it to get rid of the half we double the other side then to get rid of the mass from the right hand side well we're multiplying by it on the right so we just divide by it on the left finally to get rid of the square on the V we square root the other side so speed V is equal to 2 * the kinetic energy divided by the mass or square rooted then just pop in your numbers punch it into your calculator and boom you got your answer you could also equate elastic potential energy and kinetic energy say if a toy car is pulled back on a spring and let go there is a shortcut with the whole GP Tok scenario by the way if we just equate the two equations you'll notice that mass m is on both sides so they actually cancel out so rearranging this we find that V is equal to the < TK of 2 g h so really we only need to know the height from which something Falls in order to know its speed at the bottom if you have to rearrange the GP equation just remember that the two things you have to move from the right hand side have to go on the bottom of the left hand side multipli together in Brackets you could get a situation where for example the roller coaster has more gpe at the top than k at the bottom where's the rest of the energy gone you might ask well it must have been lost to the surroundings so that means it cannot be a closed system this could be due to work done against air resistance or friction work is just another word for energy used by the way this really does belong in the particles topic but for some reason it's here so we're going to cover it now it's the specific heat capacity practical we can find the specific heat capacity of a material by heating it up and measuring the change in its temperature for example we can use an electric heater that slots into cylinders made of different Metals we turn the heater on use a voltmeter to measure the PD and ameter to measure the current and we multiply these to get power more on this later by the way we use a balance to measure the mass of the block we use a timer and a thermometer to measure how much the temperature of the block has increased by in a certain time say 60 seconds we take the power and we multiply it by the time to get the energy that's gone into the block and then we pop these numbers into our rearranged shc equation the issue is that while heating some energy will be transferred to the surroundings which means that the temperature change that we measure will be less than what it should be so invariably our final value for the shc will be higher than the True Value power is just the rate of energy transferred any rate is a change in something divided by time here's the equation P equal e / T the unit for power is W for wats but this is just the same as Jews per second so my laptop has a 200 W power supply which just means that it uses 200 Jews of energy every second to find out how much energy it uses in a minute we just rearrange this equation so e is equal to P * T this is how you'll see it in your formula sheet by the way efficiency is a measure of how much energy going into a system is used usefully it's just a ratio or a fraction so we calculate it by doing the bit divided by the lot so in this case it's the useful energy out divided by the total energy in it also works with power too let's say that my power supply only supplies 120 wat of useful power to the laptop even though it uses 200 so its efficiency is 120 / 200 which is 0.6 as a decimal multiply that by 100 to turn it into a percentage and that means that it's 60% efficient you could be asked to give efficiency as a decimal or a percentage that means that 40% of the power or energy in is wasted this is usually as heat lost to the surroundings as usual if houses or other buildings don't have sufficient insulation a lot of heat can be lost through walls Windows Doors and the roof Etc just for triple real quick we can do a practical on this by wrapping up cans with different insulating materials or different thicknesses of the same material pouring in hot water from a kettle and measuring the temperature after a certain amount of time the higher the temperature is at the end the better the insulation energy sources are not the same as energy stores rather energy sources are where we harness energy from in the world around us finite or non-renewable sources include fossil fuels like coal oil and gas all burn to create heat for example in electrical power stations finite means that once used up no more can be obtained nuclear fuel like uranium is also finite although would not run out for a very long time renewable sources include wind power hydroelectric power stations both of these are used to turn generators to generate electricity solar pan convert light energy into electricity directly geothermal power stations involve water being pumped deep underground to be heated and biofuel is the term for any biological matter that's burned to produce energy so I hope you found that helpful leave a like if you did and pop any questions or comments below I'll see you in the next video