[Music] hi welcome back to three sighs lessons cold UK by the end of this video you should be able to describe the difference between distance and displacement you should then be able to state what's meant by speed and finally you should be able to calculate the speed of a moving object I'm showing you a car moving along a road from point A to point B the car moves a distance of 500 meters along the road now this brings us to a key point about distance distance simply tells us how far an object moves distance does not involve direction so all I saying here is that the car moved 500 meters we're not saying anything about the direction the car moved in so because it's got magnitude but no direction distance is a scalar quantity now displacement tells us the distance an object moves in a straight line from the start point to the finish point on displacement must include the direction of that straight line so I'm showing the displacement here in this case the displacement was 380 meters east now because displacement includes both magnitude and direction displacement is a vector quantity now the speed of an object tells us the distance the object traveled in the given time speed is a scalar quantity because it does not involve direction I'm showing you the equation for speed here the speed is the distance traveled divided by the time taken you are not given this equation in the exam so you need to learn it I'm also showing you the triangle for this equation in case you prefer to use that you do need to be careful though in physics the symbol for speed is V and the symbol for distance is s so don't get them confused here's a typical question a car traveled the distance of 260 meters and 20 seconds calculate the speed of the car so pause the video now and try this yourself ok so the speed is the distance traveled divided by the time taken in this case the distance is 260 meters and the time taken is 20 seconds put in these into the equation gives us a speed of 13 meters per second okay now I'm showing you some typical speeds here and you could be asked these in your exams so you do need to learn them normal walking speed is around 1.5 meters per second learning speed is around 3 meters per second and the speed of cycling is around 6 meters per second now I should point out that these can depend on several factors for example a younger fitter person will generally be able to achieve a faster speed than an older or unfit person the speed also depends on the terrain for example people move more rapidly on flat ground rather than moving uphill and finally the speed depends on the distance traveled people who are learning the long distance tend to run faster at the start when they're less tired now you could also be asked to state other speeds as well so I'm showing you those here these are also worth learning a car on a main road has a speed of around 13 meters per second a fast train in the UK has a speed of around 50 meters per second and a cruising aeroplane has a speed of around 250 meters per second now sound is much faster than all of those a typical value for the speed of sound in air is 330 meters per second however the speed of sound in air can vary for example sound travels faster on warmer days than cooler ones it's really important to understand that the speed of a moving object is rarely constant for example a car slows down and speeds off at different points during a journey but to make calculations easier we tend to calculate the average speed over the total length of the journey now if we go back to a previous equation we can rearrange this to calculate the distance travelled by an object moving at a constant speed the distance n meters equals the speed and meters per second multiplied by the time in seconds and again you're not giving this in the exam so here's a question for you a car is moving at a constant speed of 12 meters per second for 8 seconds calculate the distance traveled by the car so pause the video now and try this yourself ok to find the distance we multiply the speed by the time in this case the speed was 12 meters per second and the time was eight seconds multiplying these together gives us a distance of 96 meters remember you'll find plenty of questions on speed and distance in my revision workbook and you can get that by clicking on the link above [Music]