[Music] hi and welcome back to three sighs lessons Cole you K by the end of this video you should be able to describe what's meant by the stopping distance of a vehicle you should then be able to estimate how the distance for a vehicle to make an emergency stop varies with speed and finally you should be able to describe the fact as I can affect the thinking distance on the braking distance okay now a key issue in driving a car is how quickly it can stop in an emergency I'm showing you here a car driving along the road imagine that the driver of the car spots an obstruction for example a child the driver will apply a force to the brake and come to a stop the stopping distance is the total distance traveled from when the driver first spots the obstruction to when the car stops now we can divide the stopping distance into two parts the thinking distance is the distance travelled by the car during the drivers reaction time the reaction time is the time taken for the driver to spot the obstruction make a decision and then move their foot to the brake the braking distance is the distance the car travels from when the driver applies the brakes to when the car stops so as you can see both the thinking distance on the braking distance together make up the stopping distance now there is one key idea here the greater the speed of the vehicle the greater the stopping distance assuming that the same braking force is applied I'm showing you here how the stopping distance varies with speed for a typical family car now a common speed limit in the UK is 30 miles per hour at this speed a typical family car takes around 23 metres to stop that's the equivalent of six car lengths as we said before the thinking distance is the distance travelled by the car during the drivers reaction time so we're gonna look at that now the reaction time varies from person to person under typical ranges between Northpoint 2 seconds unknot 0.9 seconds we can measure a person's reaction time by using a ruler one person holds the ruler and a volunteer places the fingers on either side the rulers then dropped on the volunteer has to catch it the further the ruler falls before it's caught the longer the reaction time by measuring the distance at the lunar fell we can look the reaction time up in a table now it's really important that a driver has a shortest possible reaction time in other words they can react very quickly for example if they see an obstruction a tire driver will have a longer reaction time than one who's alert alcohol and certain drugs can also make the reaction time longer and finally distractions in the car such as a mobile phone will also increase the drivers reaction time so because these factors all increase the reaction time they also increase the thinking distance now the braking distance can also be affected by certain factors wet or icy conditions reduce the friction between the tires on the road and increase the braking distance the braking distance will also increase if a car has worn tires and again that's because this reduces the friction between the tires and the road finally worn brakes also increase the braking distance we're going to be looking at brakes in the next video remember you'll find plenty of questions on stopping distance in my vision workbook and you can get that by clicking on the link above [Music]