Distance-Time Graph- Grade 7 Physics.pptx

Grade 7- Physics (Q3)

1. Understanding the relationship between distance, speed and time Representing Journeys Using Distance-Time Graphs

2. Where shall we go? Liverpool Football Club ground Sydney Opera House The Taj Mahal Tower Bridge in London Let’s find out, as a class, the distance between our school and one of these destinations. How long would it take to get there, and what means of travel should we consider?

3. Today, you will... Explain what a distance-time graph is and what it represents Interpret the slopes in distance-time graphs Calculate the speeds in distance-time graphs

4. 0 m 5 m 10 m 15 m 0 s 5 s 10 s 15 s What do you notice about the distance of the ball?

5. 0 m 5 m 10 m 15 m 0 s 5 s 10 s 15 s What do you notice about the distance of the ball? In the picture, the ball is moving at a constant speed , so it covers the same distance in each interval of time. This is an example of uniform velocity. This means the object covers the same distance in the same amount of time, without speeding up or slowing down. It moves at a steady pace. Example: A car moving at 60 km/h due east without changing speed or direction.

6. x-axis Time Distance or Position y-axis What is a distance-time graph? A distance-time graph are motion graphs that show a change in an object’s location over time. In this type of graph, time is always plotted on the x-axis and the position is plotted on the y-axis

7. SCENARIO 1 A man standing at 10 meter position for five (5) seconds Distance Time 10 m 0 s 10 m 1 s 10 m 2 s 10 m 3 s 10 m 4 s 10 m 5 s

8. Distance Time 10 m 0 s 10 m 1 s 10 m 2 s 10 m 3 s 10 m 4 s 10 m 5 s Time (sec) Distance (m)

9. Time (sec) Distance (m) The horizontal straight line in the graph means that the slope is equal to zero indicating that the object is at rest or not moving. STATIONARY MOTION

10. SCENARIO 2 A man walks 4 meter east for 4 seconds Distance Time 0 m 0 s 1 m 1 s 2 m 2 s 3 m 3 s 4 m 4 s

11. Distance Time 0 m 0 s 1 m 1 s 2 m 2 s 3 m 3 s 4 m 4 s Time (sec) Distance (m)

12. Time (sec) Distance (m) The diagonal line that slopes upward to the right shows a constant and positive slope. This indicates that distance is increasing constantly with time. The object moves at a constant speed. UNIFORM VELOCITY

13. SCENARIO 3 Distance Time 0 m 0 s 2 m 1 s 5 m 2 s 10 m 3 s 18 m 4 s 30 m 5 s A cyclist starts pedaling on a flat road and approaches an uphill slope. As the cyclist begins climbing the slope, they pedal harder and accelerate. The speed increases steadily as the cyclist gains momentum.

14. Time (sec) Distance (m) Distance Time 0 m 0 s 2 m 1 s 5 m 2 s 10 m 3 s 18 m 4 s 30 m 5 s

15. Time (sec) Distance (m) Curved lines indicate that speed is changing. In this graph, the line curving upwards shows that the object is increasing its speed. As time passes, the change in distance increases. ACCELERATING

16. SCENARIO 4 Time Distance Time 30 m 0 s 28 m 1 s 24 m 2 s 18 m 3 s 10 m 4 s 0 m 5 s A car is moving toward a stoplight. As it gets closer, the driver gradually applies the brakes, causing the car to decelerate. The car's speed decreases over time, and it covers less distance in each second until it comes to a stop.

17. Time Time (sec) Distance (m) Distance Time 30 m 0 s 28 m 1 s 24 m 2 s 18 m 3 s 10 m 4 s 0 m 5 s

18. Time Time (sec) Distance (m) The speed is changing as shown by the slope of the line. In this graph, the line curving downwards shows that the object is decreasing its speed. The change in distance decreases as time passes. DECCELERATING

19. Tisha’s Journey to School Tisha left home and walked at a constant speed for the first 6 minutes, covering 20 meters. She saw her best friend, and they stopped at a corner shop for 2 minutes. They realised they would be late for their class and decided to walk at a constant speed, covering 60 meters in just 2 minutes. How can you oganise the given details and model the change in Tisha’s positions over time?

20. Tisha’s Journey to School We can start by highlighting the details from Tisha’s journey and organising them in a table format. Time elapsed (min) Distance (m) from the starting point Description At home 6 20 Walking at a constant speed 8 20 Stopping and chatting with her best friend 10 60 Walking briskly but at a constant speed

21. We can then use a distance-time graph to plot the data and represent Tisha’s journey. What is a distance-time graph and how do we interpret it? Time (min) Distance (m) Tisha’s Journey to School

22. Interpreting Distance-Time Graphs Time Distance or Position slope constant speed The gradient of the line (or slope) on a distance-time graph tells us about the speed of the object. A straight diagonal line means the object is travelling at a constant speed. The steeper the slope, the faster the object is moving.

23. Interpreting Distance-Time Graphs Time Distance or Position slope constant speed The gradient of the line (or slope) on a distance-time graph tells us about the speed of the object. A straight diagonal line means the object is travelling at a constant speed. The steeper the slope, the faster the object is moving.

24. Time Distance or Position constant speed, returning to the starting point When the line on a distance-time graph slopes downwards , it represents ‘returning to the starting point’. If the line descends all the way back to the x -axis, the object has fully returned to its starting point. Interpreting Distance-Time Graphs

25. Learning Check What do these two graphs mean? How would you describe Tisha's journey if this is part of her graph? Time Distance or Position Time Distance or Position A B

26. Answer Key Learning Check What do these two graphs mean? How would you describe Tisha's journey if this is part of her graph? Time Distance or Position A An object is at rest Tisha is stationary Time Distance or Position B An object moves fast at a constant speed Tisha is walking speedily at a constant rate

27. Interpreting Tisha’s Journey At A , Tisha is moving at a constant speed. At B , she is at rest or stationary. At C , she is again moving at a constant speed, but this time faster than her speed in point A. Let’s look again at Tisha’s journey to school! A B C Time (min) Distance (m)

28. Calculating Speed from Distance-Time Graphs gradient = change in y values change in x values The gradient or slope in a distance-time graph equals the speed . The gradient is calculated using: Remember: The unit of speed depends on the units given in the x - and y -axes.

29. Calculating Tisha’s Speed Let’s try to calculate Tisha’s speed on the first leg of her journey! gradient = change in y values change in x values gradient = 20 m - 0 6 min - 0 gradient = 3.33 m/min Tisha walked at a speed of 3.33 metres per minute in section A. Time (min) Distance (m) A B C

30. Try This! Calculate Tisha’s speed in section C. How does it compare to her speed in section A? Time (min) Distance (m) A B C

31. Calculate Tisha’s speed in section C. How does it compare to her speed in section A? gradient = 60 m - 20 m 10 min - 8 min gradient = 20 m/min Tisha walked faster towards the end of her trip than when she first started out from home. Time (min) Distance (m) A B C Answer Key Try This!

32. A Recap gradient = change in y values change in x values The gradient (slope) of the line tells us about the speed of travel. The steeper the line, the faster an object is travelling. Distance-Time Graph Gradient Calculating Speed It is a graph that shows how an object’s position or distance covered changed over time. The speed of an object can be calculated from the gradient of a distant-time graph using:

33. Your Journey to School Sketch a simple diagram of your journey to school with approximate timings. Organise the data in a table format. Then, prepare a distance-time graph to represent your journey.

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