 Have you ever wondered, when driving in a car, why you are pushed back into your seat when the driver hits the gas pedal? This is because the car is accelerating and your body isn't. Your body is slowly catching up to the speed of the car. In this video, we're going to look at different types of acceleration and compare acceleration in different experiences. So what is acceleration? Acceleration is the rate in which an object changes its speed. It can be quick or it can be slower. Accelerate means to speed up and decelerate means to slow down. There are two things that affect acceleration. Firstly, how much the speed changes. So is it from 0 to 100 km per hour? Or is it only from 40 km per hour to 50 km per hour? And secondly, how much time the change in speed takes. So have you gone from 0 to 100 km per hour in 10 seconds or 20 seconds? So how can acceleration be measured? Since acceleration is the rate at which an object changes its speed, you can say that acceleration is the change of speed over time. The unit of acceleration is meters per second squared. If we look at acceleration on a velocity time graph, the different options look like this. This is faster acceleration than this because it's steeper, so it's reaching each velocity in less time. No acceleration is happening and then decelerating. So slowing down is coming back from 8 m per second velocity back down to 0 m per second. What is constant acceleration? It is when the speed or velocity is increasing at the same rate over the same period of time. So a straight line. But maybe you start off just giving a little gas and then once you're on the motorway you want to hit full speed sooner, so you accelerate faster. This would be a curve line like this on the graph. Or maybe you're decreasing your acceleration. So you started off with a big push accelerating quickly and now you're accelerating up to your max speed at a slower rate. What do you think this would look like on a graph? So your velocity is increasing but at a slower rate than before. Pause the video and have a think. Did you think a curve like this? The car is still accelerating but the rate of acceleration is slowing. Can you think of acceleration in the real world? Pause the video and have a think. Obviously any vehicle is driving. But elevators, rockets, aeroplanes, amusement parks, a diver jumping off a cliff accelerates towards the water, a skier on a mountain. There are so many examples. So what are some common acceleration values? We already know acceleration is measured in m per second squared. A common hatchback car can reach 100 km an hour in 6.7 seconds. This gives it an acceleration of 4.15 m per second squared. This calculation is because we have to turn the 100 km into meters first, then turn the per hour into seconds by turning it into minutes and then seconds and divide it by 6.7 seconds to get the acceleration. How does a Formula 1 car and a roller coaster compare to the car and the space shuttle? Pause the video and work it out. Did you get them right? The roller coaster ride actually has the fastest acceleration. In this video we have learnt that acceleration is the rate at which an object changes its speed. Two factors affect it. How much change in speed there is and how quickly that change happens. Hence the equation.