9-1 9-2 9-3

1. 9-1 9-2 9-3 Location

2. Concept Development 9-1 Created for CVCA Physics By Dick Heckathorn 4 January 2K + 5

3. Circular Motion • a.If there is no relative motion between the train and the edge of the platform, how fast must the train move compared to the rim speed of the rotating platform?

4. Circular Motion • b. Why is the stairway located at the center of the platform?

5. White Water Landing

6. Circular Motion • a. How is the size of the round platform and train speed related to the amount of time that passengers have for boarding?

7. Circular Motion • b. Why would this rotating platform be impractical for high speed trains?

8. Circular Motion • a. The platform is not rotating on its axis and the people are at rest.

9. Circular Motion • b. When the platform rotates, the person in the middle stands as before. The person at the edge must lean inward as shown. • b. Make a sketch of the missing people to show how they must lean in comparison.

10. Circular Motion • The sketch on the left shows some toy ducks floating on the water. • The sketch on the right shows the container rotating about a central axis at constant speed. • Make a sketch showing the orientation of the other two ducks with respect to the water surface.

11. Circular Motion • The sketch on the left shows the water surface when the tire is not rotating. • The sketch on the right show the water surface when the tire and water rotate about its central axis.

12. Circular Motion • Now suppose the tire is rotating about the same axis while orbiting in outer space. • Draw the shape of the water surface in the cross-sectional view above. • Where would the people be and how would they be affected? • Scale up the rotating tire model to a rotating space habitat orbiting in space.

13. Concept Development 9-2 Created for CVCA Physics By Dick Heckathorn 15 December 2K+3

14. Accelerating & Circular Motion • You’re in a car at a traffic light. The light turns green and the driver steps on the gas. v a • a. Your body lurches: backward • b. The car accelerates: forward • c. Force on car acts: forward

15. Accelerating & Circular Motion • You’re driving along and approach a stop sign. The driver steps on the brakes. v a • a. Your body lurches: forward • b. The car accelerates: backward • c. Force on car acts: backward

16. Accelerating & Circular Motion • You continue driving and round a sharp curve to the left at constant speed. a v • a. Your body leans: outward • b. Direction of acc. is: inward • c. Force on car acts: inward

17. Accelerating & Circular Motion 4. In general, the directions of lurch and acceleration, and therefore the direction of lurch and force are: the same not related opposite

18. Accelerating & Circular Motion • a. If it moves faster, its direction changes: faster slower 5. The whirling stone’s direction of motion keeps changing. • b. This indicates that as the speed increases, acceleration: • increases decreases stays the same

19. Accelerating & Circular Motion 6. Consider whirling the stone on a shorter string – that is, of smaller radius a. For a given speed, the rate that the stone changes direction is: less more the same b. This indicates that as the radius decreases, acceleration: increases decreases stays the same

20. Centripetal Force p 40 Ftable on rock Fstring on rock Fearth on rock 1. A rock tied to a post moves in a circle at constant speed on a frictionless horizontal surface. All the forces acting on the rock are shown.

21. Centripetal Force p 40 Ftable on rock Fstring on rock Fearth on rock a. The vector responsible for circular motion is: Fstring on rock b. The net force on the rock is: Fstring on rock

22. Centripetal Force p 40 Fequilibrium T Fstring on rock Fnet Fearth on rock W 2. The rock is tied to a string and swings in a circular path. It is not resting on a surface. No friction. Find the net force.

23. Centripetal Force p 40 T Fnet W a. What is the direction of Fnet? to center b. Does Fnet lie in plane of circular path? Y c. Is Fnet horizontal Component of T? Yes d. Is Fnet the centripetal force? Yes

24. Centripetal Force p 40 Fdisk on rock Ffriction Fearth on rock 3. The rock rides on a horizontal disk that rotates at constant speed about the vertical axis. Friction prevents the rock from sliding. Draw and label all vectors.

25. Centripetal Force p 40 Fdisk on rock Ffriction Fearth on rock b. Which force is centripetal? Ffriction c. Which force provides net force? Ffriction d. Why do we not say net force is zero? because centripetal acceleration is not zero

26. Centripetal Force p 40 Ffriction Fwall on rock Fearth on rock 4. Now the rock is held in place by friction against the inside wall of the rotating drum. Draw and label all forces that act on the rock.

27. Centripetal Force p 40 Ffriction Fwall on rock Fearth on rock a. Which force is centripetal? Fwall on rock b. Which force provides net force? Fwall on rock

28. Centripetal Force p 40 Fe Fwall on rock Fnet Fearth on rock 5. The rock rests against a frictionless wall of the cone which rotates about its vertical axis. The rock does not slide up or down. Draw and label all forces on the rock.

29. Centripetal Force p 40 Fwall on rock Fnet Fearth on rock a. Should Fnet lie in the plane of the circular path? Yes b. Why It provides the centripetal force for circular motion

30. Concept Development 9-3 Created for CVCA Physics By Dick Heckathorn 15 December 2K+3

31. 1. From Bob’s point of view, he is at rest and sees Suzie moving: • clockwise • counter clockwise

32. 2. When Bob rides in the opposite direction as the habitat rotates, Suzie sees him moving: • faster • slower

33. 3. As Bob’s bicycle speedometer reading increases, his rotational speed • decreases • and the normal force that feels the weight • decreases. • So friction between the tires and the floor • decreases.

34. 4. When Bob gets his speed up to 30 km/hr, as read on his bicycle speedometer, Suzie sees him: • motionless

35. 5. Bouncing off the floor a bit while riding at 30 km/hr, and neglecting wind effect, Bob: • hovers in midspace as the floor whizzes by him at 30 km/hr. • and he finds himself • in the same frame of reference as Suzie

36. 6. Bob now rides in a clockwise direction, with the rotation of the habitat. Now Suzie sees him moving • faster. • 7. As Bob gains speed, the normal support force that feels like weight • increases.

37. 8. When Bob’s speedometer reading gets up to 30 km/hr, Suzie sees him moving • 60 km/hr • and Bob finds himself: • pressed harder against the floor.

38. Next, Bob goes bowling. You decide whether the game depends on which direction the ball is rolled!

39. That’s all folks!

43. Bob is standing on a people mover (conveyor belt) at the airport which is moving toward the west at a speed of 6.0 m/sec. • Susie is standing to one side looking at Bob.

44. 1. From Bob’s point of view, he is at rest and sees Suzie moving: • westward • eastward • not moving

45. Thus Bob sees Suzie moving at the same speed but in the • same • opposite • direction.

46. 3. Bob starts walking to the east. Suzie will see Bob • speeding up • or • slowing down

47. As Bob walks faster and faster, Suzie sees Bob • speeding up more • or • slowing down more

48. When Bob gets his speed up to 6.0 m/s, Suzie sees him • moving at 6 m/s • motionless • moving at 12 m/s

49. 6. Bob makes a slight push on the conveyer belt while walking at 6.0 m/s (east). • From Suzie’s point of view, he • will be moving towards the east • will be motionless • will be moving towards the west

50. 7. Bob now finds himself • in the same frame of reference • moving west • moving east • relative to Suzie