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Velocity-time graph

Gradient gives acceleration. Velocity-time graph. Velocity/. Time/s. Velocity-time graph. Velocity/. Time/s. Velocity-time graph. Velocity/. Time/s. Velocity-time graph. Velocity/. Time/s. Example 8:. Describe the motion of the object. Velocity/. Time/s. Example 8:.

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Velocity-time graph

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  1. Gradient gives acceleration Velocity-time graph Velocity/ Time/s

  2. Velocity-time graph Velocity/ Time/s

  3. Velocity-time graph Velocity/ Time/s

  4. Velocity-time graph Velocity/ Time/s

  5. Example 8: Describe the motion of the object. Velocity/ Time/s

  6. Example 8: • From to , the object is moving from rest with increasing velocity. The object has uniform acceleration of . • From to , the object is moving with constant velocity of . • From to , the object is moving with decreasing velocity. The object has uniform acceleration of until it comes to a stop.

  7. Need a break?

  8. Area under v-t graph is displacement Velocity-time graph A car moves at constant velocity of for a period of 30 s. What is the displacement of the car? Displacement = velocity time = 25 30 = 750 m Velocity/ Time/s

  9. Velocity-time graph • Gradient of v-t graph gives acceleration. • Area under v-t graph gives displacement.

  10. Example 9: The graph shows the velocity of the object over a period of time. Calculate the average velocity of the object from 0 s to 8 s. Velocity/ Time/s

  11. Acceleration due to gravity • Video on golf ball and bowling ball • Question: What does this tell us about how objects fall when released from the same height? • The change in velocity is the same hence they take the same time to reach the ground regardless of their masses. (Ignoring air resistance) • Not in syllabus: Find out about Galileo Galilei’sfalling bodies experiment

  12. Acceleration due to gravity • Acceleration due to gravity, g is a constant. • The value of g is 9.81 • For O level, we take it as 10 . • g is constant for object close to the Earth. • Not in syllabus: Is g really constant everywhere on the surface of the Earth? Where is g minimum or maximum on the surface of the Earth?

  13. Example 10: An object is released from rest at the top of a building. If the acceleration due to gravity is 10 and the object takes 5 s to reach the ground (neglecting air resistance), • What is the speed of the object just before it hits the ground? • What is the height of the building?

  14. Example 11 The graph shows the velocity of an object over a period of 8 s. Velocity/ Time/s

  15. Example 12 A cyclist is travelling along a path and its displacement-time graph is as shown. Deduce and sketch its velocity-time graph. Displacement/m Time/s

  16. Displacement/m Time/s Velocity/m s-1 Time/s 0 10 2030

  17. 10 minute quiz

  18. Exit card

  19. What you have learnt (a) state what is meant by speed and velocity (b) calculate average speed using distance travelled / time taken (c) state what is meant by uniform acceleration and calculate the value of an acceleration using change in velocity / time taken (d) interpret given examples of non-uniform acceleration (e) plot and interpret a displacement-time graph and a velocity-time graph

  20. What you have learnt (f) deduce from the shape of a displacement-time graph when a body is: • at rest • moving with uniform velocity • moving with non-uniform velocity (g) deduce from the shape of a velocity-time graph when a body is: • at rest • moving with uniform velocity • moving with uniform acceleration • moving with non-uniform acceleration

  21. What you have learnt (h) Calculate the area under a velocity-time graph to determine the displacement travelled for motion with uniform velocity or uniform acceleration (i) state that the acceleration of free fall for a body near to the Earth is constant and is approximately 10

  22. Homework • 4 practice questions (Worksheet 2) • 2 not in syllabus questions (optional) • By 5thApril, next Friday.

  23. References & links • Falling bodies experiment http://www.youtube.com/watch?v=Z789eth4lFU • “How steep is your slope?” song. http://www.youtube.com/watch?v=ds_7fPIRFPM • Falling feather and ball bearing http://www.youtube.com/watch?v=_XJcZ-KoL9o

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