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Speed, velocity and acceleration

Speed, velocity and acceleration. 1 Both Mr Rabbit and Mr Tortoise took the same round trip, but Mr Rabbit slept & returned later. Who runs faster?. No, I travelled more distance every second I ran. Me, as I spent less time on the trip. Who is right?.

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Speed, velocity and acceleration

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  1. Speed, velocity and acceleration

  2. 1 Both Mr Rabbit and Mr Tortoise took the same round trip, but Mr Rabbit slept & returned later.

  3. Who runs faster? No, I travelled more distance every second I ran. Me, as I spent less time on the trip. Who is right?

  4. 2 Some kid is lost in the woods. (a) If he walks at a speed of 4 km/hr, try to locate his possible positions on the map.

  5. 2 Some kid is lost in the woods. (b) What else is important to find the kid? The direction in which he has been walking.

  6. Reference Points

  7. All Motion is relative All motion isrelativeto a reference. This means that we describe motion of an object relative to some other object

  8. All Motion is relative In our environment, the reference for motion is the earth’s surface, and speeds are measured relative to the earth The earth moves at 107,000 km/h relative to the sun

  9. Calculating Motion and Speed

  10. 1 Speed How can we describe how fast an object moves? E.g. A car on Beltway 8 travels 90 km in 1 hour. We say that the car travels ata speedof 90 km/hr.

  11. 1 Speed How can we describe how fast an object moves? Speed is a measure of how fast something moves. Speed = distance travelled per unit of time SI unit: m/s or km/h(for long distances)

  12. a Average speed 1 Speed A car travels at 50 km/h, slows down to 0 km/h, and speeds up again to 60 km/. Its average speed over the whole journey overall distance travelled = total time of travel

  13. Question 1 • A bug crawls 10 cm in 5 sec. What was the bug’s approximate speed in cm/sec? 2 cm/sec

  14. a Average speed 1 Speed Average speed does not tell the variations during the journey. On most trips, the speed at any instant is often different from the average speed.

  15. b Instantaneous speed 1 Speed = speed at any instant Instantaneous speed The word ‘speed’ alone  instantaneous speed Instantaneous speed  distance travelled inan extremely short time interval

  16. b Instantaneous speed 1 Speed Speedometer tells the car’s speed at any instant!

  17. ( ) Average speed = 10.49 s Question 2 The world record for women’s 100-m race is 10.49 s. What is the average speed? 100 m = 9.53 m/s

  18. Velocity

  19. direction magnitude (speed) 2 Velocity Velocity is... a speed in a given direction or rate of change of displacement. a vector quantity velocity

  20. 2 Velocity a Speed with direction Train engineers use speed only. speed = 90 km/h Pilots use velocity (direction & speed). speed = 300 km/h direction = west

  21. 2 Velocity b Average velocity overall displacement Average velocity = total time of travel direction of overall displacement direction of velocity =

  22. Question 3 • A student runs around a circular track that is 1000m in length in a time of 30 min. What is the average velocity of the student? 0 m/min If the student runs completely around the track, they are back where they began. So their overall displacement is zero.

  23. 2 Velocity c Instantaneous velocity The velocity atany instant is calledinstantaneous velocity. If a car moves at a constant velocity... … its average and instantaneous velocities have the same value.

  24. Question 4 • Which of these is a correct velocity? • 55 miles per hour • 15 kilometers per second • 30 meters per second east • 400,000,000 meters per hour

  25. Acceleration

  26. 3 Acceleration When an object moves faster and faster, its speed is increasing (velocitychanged).

  27. 3 Acceleration When an object moves slower and slower, its speed is decreasing (velocity changed).

  28. 3 Acceleration When an object changes direction, its velocity changes too.

  29. direction speed 3 Acceleration Acceleration measures the change in velocity Acceleration = velocity per unit time overall change in velocity = total time taken vector quantity Unit: m/s/s = m/s2

  30. 3 Acceleration If a car accelerates at 2 m s–2, what does that mean? v = 0 t = 0 v = 2 m s–1, v = 2 m s–1 t = 1 s 1 m v = 4 m s–1, v = 2 m s–1 t = 2 s 3 m t = 3 s v = 6 m s–1, v = 2 m s–1 5 m

  31. 40 m/s – 20 m/s 60s – 15 s 20 m/s = 45 s Question 5 Tommy accelerates from 20 m/s at 15 sec (t1) to 40 m/s at 60 sec (t2). What is his avg. acceleration between t1 and t2? Avg. acceleration = = .44 m/s2

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