[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to describe what's meant by kinetic energy you should then be able to calculate kinetic energy for a moving object all of the objects I'm showing you here have got kinetic energy we've got a train a Formula One car and a roller coaster so what exactly is kinetic energy kinetic energy is the energy stored in moving objects so a stationary object such as a parked car has got no kinetic energy now we calculate kinetic energy by using this equation kinetic energy in Jews is 0.5 multiplied by the mass of the object in kilograms multiplied by the speed of the object squared and the unit of speed is me/ second now I should point out something really important here you're not given this equation in the exam so you've got to learn it so so I'm showing you here a car traveling at a constant speed let's take a look at the energy changes taking place the car runs on petrol and that's a store of chemical energy a chemical reaction takes place in the engine and some of the energy is converted to kinetic energy stores as the car moves so we're going to calculate kinetic energy of a moving object here's a sample question a car with a mass of 700 kg is moving with a speed of 20 m/s Cal calate the kinetic energy of the car so here's the equation kinetic energy equals .5 MTI the mass multiplied by the speed squared the mass is 700 kg and the speed is 20 m/s putting these numbers into the equation gives us a kinetic energy of 140,000 Jew now scientists often convert Jews into kles to do this we divide by 1,000 so in this case the kinetic energy is 140 k here's a question for you to try a cyclist and bike have a total mass of 100 kg and a speed of 15 m/s calculate the kinetic energy you should pause the video now and try this yourself okay so here's the equation and remember you need to learn this kinetic energy is .5 multiplied by the mass multiplied by the speed squared the mass is 100 kg and the speed is 15 m/s putting these numbers into the equation gives us a kinetic energy of 11,250 Jew dividing this by 1,000 gives us 11.25 K here's a final question for you a tennis ball is traveling at 50 m per second and has a kinetic energy of 75 Jew calculate the mass of the tennis ball pause the video and try this yourself okay now on this question we're given the kinetic energy and we've got to use this to calculate the mass so we need to rearrange the equation for kinetic energy like this the mass is the kinetic energy divided by .5 multipli by the speed squared putting our numbers into the equation gives us a mass of .06 kg for the tennis ball remember you'll find plenty more questions on calculations involving kinetic energy in my vision workbook which you can get by clicking on the link above okay so hopefully now you should be able to describe what meant by kinetic energy you should then be able to calculate kinetic energy for a moving [Music] object