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# Circular Motion

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• ### Circular Motion

1. 1. Physics Cir cu lar Mo tion
2. 2. Circular motion <ul><li>Revision </li></ul><ul><li>Circular motion in horizontal </li></ul><ul><li>Vertical circular motion </li></ul><ul><li>Loop-the-loop </li></ul>
3. 3. Revision <ul><li>Newton’s Laws </li></ul><ul><li>Circular motion in horizontal circles </li></ul><ul><li>Centripetal force and acceleration </li></ul><ul><li>Angular velocity, frequency & linear velocity </li></ul>
4. 4. Newton’s first Law <ul><li>A body continues in a state of </li></ul><ul><li>rest or uniform motion in a </li></ul><ul><li>straight line unless it is acted </li></ul><ul><li>upon by external forces. </li></ul>
5. 5. No external force The body remains at rest. The body moves with a constant speed . Newton’s first Law
6. 6. <ul><li>The rate of change of momentum </li></ul><ul><li>of a body is proportional to and </li></ul><ul><li>in the same direction as the </li></ul><ul><li>resultant force that acts on it. </li></ul>Newton’s second Law
7. 7. For fixed force A body with a larger mass moves with a smaller acceleration . A body with a smaller mass moves with a larger acceleration . Newton’s second Law
8. 8. For fixed mass A body with a smaller net force moves with a smaller acceleration . A body with a larger net force moves with a larger acceleration . Newton’s second Law
9. 9. <ul><li>If one body exerts a force on </li></ul><ul><li>another, there is an equal and </li></ul><ul><li>opposite force, called reaction, </li></ul><ul><li>exerted on the first body. </li></ul>Newton’s third Law
10. 10. Body A exerts a force on body B, then body B exerts an equal and opposite force on body A. Newton’s third Law Body A Body B Force on B by A Force on A by B
11. 11. Newton’s third Law
12. 12. Circular Motion in horizontal circles
13. 13. Circular Motion in horizontal circles Angular velocity  =  / t Linear velocity v =  r Centripetal force F = m r  2 = m v 2 / r Centripetal acceleration a = r  2 = v 2 / r
14. 14. Circular Motion in horizontal circles Conical pendulum
15. 15. Circular Motion in horizontal circles Conical pendulum Do you remember what kind of forces provides the centripetal force to the bob ? Tension T Weight mg Centripetal force
16. 16. Vertical circular motion Bucket and water Does the water spill out the bucket when whirling ? If no, why doesn’t it spill out ?
17. 17. Vertical circular motion Bucket and water What kind of motion does the bucket perform ? Vertical circular motion What kind of force provides the centripetal force F c to the bucket ? Tension T Weight mg
18. 18. Vertical circular motion Bucket and water What kind of force provides the centripetal force F c to the bucket at the highest position ? F c = T + mg Tension T Weight mg
19. 19. Vertical circular motion Bucket and water What kind of force provides the centripetal force F c to the bucket at the lowest position ? F c = T - mg Tension T Weight mg
20. 20. Vertical circular motion Bucket and water What kind of force provides the centripetal force F c to the water at the highest position ? F c = R + W Reaction of the bucket R Weight of water W
21. 21. Vertical circular motion Bucket and water What kind of force provides the centripetal force F c to the bucket at the lowest position ? F c = R - W Reaction of the bucket R Weight of water W
22. 22. Vertical circular motion Loop-the-loop
23. 23. Vertical circular motion Loop-the-loop What kind of force provides the centripetal force F c to the mass ? The reaction of the track
24. 24. Class exercises M.C. Exercise Main menu True or False
25. 25. M.C. Question 1 <ul><li>Which of the following formula </li></ul><ul><li>shows Newton’s second Law ? </li></ul>v = r   =  / t F = ma a = v 2 / r
26. 26. M.C. Question 2 <ul><li>At which position is the tension </li></ul><ul><li>on the bucket largest ? </li></ul>
27. 27. True or False Question 1 <ul><li>If the angular velocity of the bucket </li></ul><ul><li>at the top position is too small, </li></ul><ul><li>water may spill out. </li></ul>True False
28. 28. <ul><li>In the Ocean Park , cart coast rider </li></ul><ul><li>can loop the loop by tension. </li></ul>True or False Question 2 True False
29. 29. You are wrong. Try again ! Sorry ！ 　 return
30. 30. Congratulation ! Correct ! Return