[Music] hi and welcome back to three sighs lessons Cole you K by the end of this video you should be able to calculate the velocity of an object which is accelerating at a constant rate you should then be able to describe the acceleration of an object falling through a fluid in the last video we looked at acceleration we calculate acceleration using this equation acceleration equals a change in velocity divided by the time and remember you're not in this equation in the exam now if an object accelerating at a constant rate then we can use a different equation and I'm showing you that here the final velocity squared minus the initial velocity squared equals two multiplied by the acceleration multiplied by the distance now I want to make a couple of points about this firstly you are given this equation in the exam so you don't need to learn it secondly this is pretty tricky so I think it's more likely to appear on the higher paper than the foundation I could be wrong though so if you're a foundation tier student then you do need to keep watching but please don't panic over this equation also you should pay close attention to the second part of the video as that's more straightforward here's a sample question a car is driving at a velocity of 8 meters per second it accelerates by 2 meters per second squared to a final velocity of 12 meters per second calculate the distance traveled okay so here's the equation and we're calculating the distance to do that we need to rearrange the equation like this the final velocity was 12 meters per second and the initial velocity was 8 meters per second the acceleration was 2 meters per second squared putting these numbers into the equation gives us a distance traveled of 20 meters here's a question for you to try a cyclist is moving at a velocity of 3 meters per second and accelerates to 5 meters per second over a distance of 50 meters calculate the acceleration of the cyclist now for this question have we arranged the equation for you so pause the video now and try this yourself okay so the initial velocity is three meters per second and the final velocity is five meters per second the distance travel is 50 meters putting these into the equation it gives us an acceleration of nought point one six meters per second squared here's a final question for you a train has an initial velocity of 20 meters per second it accelerates at five meters per second squared over a distance of 50 meters calculate the final velocity now in this case I'd like you to rearrange the equation yourself if a higher tier student then you should be able to do this if you're a foundation tier student then don't worry because I'll be giving you the equation in a second okay so here's the rearranged equation to calculate the final velocity I'd like you to pause the video now and carry out this calculation okay the initial velocity is 20 meters per second and the acceleration is 5 meters per second squared the distance is 50 meters put in the numbers into the equation gives us a final velocity of 30 meters per second okay we're going to finish now by looking at how objects accelerate towards the Earth I'm showing you have a skydiver who has just jumped out of an airplane now the key fact is that when any object Falls towards the surface of the earth it initially accelerates at around 9.8 meters per second squared this acceleration is due to the force of gravity acting on the object now as the skydiver Falls he experiences an upward force of friction with the air particles this is called air resistance and after some time the force of air resistance balances the force due to gravity at this point the object stops accelerating and moves at a constant velocity scientists call this the terminal velocity and you need to learn that expression this applies to any object falling through a fluid in the case of the skydiver the fluid is air but we see the same effect with an object falling through a liquid now the terminal velocity that the object reaches depends on the object some objects experience a greater force of friction due to their shape so they will have lower terminal velocity remember you'll find plenty of questions on acceleration in my revision world book and you can get that by clicking on the link above [Music]