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Circular Motion

Circular Motion. Why aren’t we getting anywhere?. AXIS OF ROTATION. This is an imaginary line through the center of the spinning. The points on the axis of rotation don’t move due to the spinning. As the circle spins the point on the axis of rotation appears is still.

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Circular Motion

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  1. Circular Motion Why aren’t we getting anywhere?

  2. AXIS OF ROTATION This is an imaginary line through the center of the spinning The points on the axis of rotation don’t move due to the spinning

  3. As the circle spins the point on the axis of rotation appears is still

  4. As the circle spins the point on the axis of rotation appears is still

  5. Here the axis of rotation is not in the center, where is it?

  6. If the axis of rotation is through the object it is called ROTATION If the axis of rotation is outside of the object it is called REVOLVING

  7. The earth rotates and revolves

  8. The earth rotates and revolves

  9. The earth rotates and revolves At the same time

  10. The time it takes an object to complete 1 cycle is called the Period, its symbol is T T What is the unit?

  11. Does the object have a constant speed? Does the object have a constant velocity? Moving in a circle at a constant speed is called uniform circular motion

  12. The speed of an object in a circular path is called its Tangential Speed, vt Its direction is always tangent to the circular path

  13. How could we calculate the balls speed? distance time

  14. For circular motion : 2pr vt = radius (m) T tangential speed (m/s) period (s)

  15. The outer dot has to move faster in order to travel the longer path in the same amount of time Which lady bug has the greater tangential speed?

  16. Does the object (at constant speed) accelerate?

  17. Acceleration v2 -v1 v2 – v1 v1 a = t v2 Why is this a bit harder here?

  18. The acceleration which keeps an object in uniform circular motion is called- Centripetal Acceleration aC centripetal means center seeking

  19. Centripetal acceleration is always pointed to the center of rotation and perpendicular to the tangential velocity aC

  20. The magnitude is given by the equation below. tangential velocity (m/s) vt2 ac = r radius (m) The faster it is going, the harder it needs to turn The smaller the radius, the harder it needs to turn a sharp turn vs. a wide turn

  21. The drum of a washing machine has a radius of 34 cm. During spin cycle the drum rotates with a tangential velocity of 5.5 m/s. a.) What is the centripetal acceleration of the clothes against the drum? b.) What is its direction? c.) What is the period of rotation?

  22. Two race cars are in a turn, the speedometer of 1 car reads a constant 60 mph and the second reads 120 mph. Compare their centripetal accelerations?

  23. The speedometer of a car reads a constant 100 mph, the radius of the second turn is ½ of that of the first. Compare the centripetal accelerations between the turns.

  24. Which penny has the greater acceleration? v2 acentripetal = r Compare the r’s .1 m .2 m Compare the v’s 2 pennies on a lazy susan demo

  25. 2pr Since v = T v2 4p2r2 acentripetal = = r r T2 4p2r ac = T2

  26. 4p2r acentripetal = T2 T = 2 s T = 1 s Compare their accelerations

  27. What is the direction of the net force on the object? What would happen to the ball if there was no net force acting on it? Is there a net force the object?

  28. The force which cause an object to travel in uniform circular motion is called the CENTRIPETAL FORCE It always points to the axis of rotation

  29. A centripetal force is NOT a “new” type of force like FN, FF, FG, FT It is simple one of the above acting in such a way to make an object travel in a circle. But how does it “Know” to always point to the center, it must be COMPLICATED???

  30. The centripetal force is always perpendicular to the velocity! ball on a string demo What is the centripetal force? How does it always point to the middle?

  31. Fg What provides the centripetal force in the scenario Note the centripetal force always points directly towards and perpendicular to the axis of “rotation”

  32. FN What provides the centripetal force in the scenario That keeps the riders moving in a circle?

  33. FF What provides the centripetal force on the penny that keeps in moving in a circle on a record?

  34. FN FN Fg What forces do you experience on a merry go round as it spins? It feels like a force is pushing you to the outside of the circle, what is the dealer of this force?

  35. A C D E F If the string were to be cut what path would the ball take? B Assume there is NO gravity

  36. Anything curved has to go if no force is acting on the ball B A C D E F

  37. Anything curved has to go if no force is acting on the ball B A D

  38. Let’s try it and find out?

  39. What direction was the ball headed just before the string broke B A D

  40. What direction was the ball headed just before the string broke D

  41. An overhead view of a car on a circular track, what provides the centripetal force

  42. What happens if friction is lost?

  43. The only (net) force in uniform circular motion is directed inward There is NO outward directed force it only feels like it. Centripetal force (tension)

  44. The tangential velocity is the velocity is would continue to have if there were no net forces acting on it Tangential Velocity Force

  45. The ball’s speed and KE never change, this means the force doesn’t do any WORK on it. WHY? FC Does its speed change? The force is always perpendicular to its motion

  46. F = ma Fcentripetal = macentripetal

  47. v2 acentripetal = r T = 2 s T = 1 s Compare the centripetal force needed, equal mass

  48. v2 acentripetal = r The velocities are equal Which requires a greater Force?

  49. When the record is spun faster which penny will fly off first? 4p2r acentripetal = T2 .1 m .2 m 2 pennies on a lazy susan demo

  50. 4p2r acentripetal = T2 Which requires a greater Force?

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