Lesson video

Hello, my name is Mr. Clasper, and today we are going to be looking at velocity-time graphs.

This graph shows the journey of a car for the first 13 seconds of a journey.

Describe what each section of the graph shows.

This part tells me that I start at zero metres per second, or for example, from rest.

This is also known as my initial velocity.

This part of my journey tells me I'm accelerating as the speed is increasing.

This is indicated by a positive gradient.

This part of my journey tells me that I've reached a speed of 35 metres per second, after six seconds.

The horizontal line tells me at this point, my speed is not changing, so I have a constant speed at this point for three seconds.

And this point tells me that I'm decelerating or decreasing in speed.

This is indicated by a negative gradient.

Have a look at these two velocity-time graphs.

What's the same and what's different? Well, if we look at our first graph, this tells us that my acceleration is constant.

This is signified with a straight line.

If I look at my second graph, I have a curve.

This means that I have a variable acceleration, as the acceleration, in this case, increases exponentially.

Here's a question for you to try.

Pause the video to complete your task and click resume once you're finished.

And here are your solutions to part a.

Here is part b.

Pause the video to complete your task and click resume once you're finished.

And here is your solution to part b.

So when we look at the graph, the maximum speed is the highest point on our graph.

And in this case, the highest point in our graph is 150 and this happens after six seconds.

Here is part c.

Pause the video to complete your task and click resume once you're finished.

And here is your solution to part c.

So a constant speed on a velocity-time graph is signified by a horizontal line.

So our horizontal line is covered over three seconds, which was our correct answer.

Here is part d.

Pause the video to complete your task, click resume once you're finished.

And here is your solution.

For this question, it would be useful if you drew a horizontal line from the y-axis at 125 and from here, we're looking at all the parts of our graph that lie above this line.

And in our case, that would happen after five seconds and before 9.

5 seconds, therefore it was a total of 4.

5 seconds that the car was travelling at or greater than 125.

And here is your final question.

Pause the video to complete your task, click resume once you're finished.

And here is the solution for your final problem.

So check your graph with ours very carefully.

Make sure you've read from the graph carefully.

You should have a constant speed after 12 seconds.

And that brings us to the end of our lesson on velocity-time graphs.

Why not have a go at the exit quiz, and show off your brand new skills.

I'll hopefully see you soon.