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Circular Motion

This demo explores circular motion and vertical circles through various examples, including tennis dodge-ball, penny & coat hanger, bucket of water & rope, and more. Learn about forces, acceleration, and the behavior of objects in circular motion.

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Circular Motion

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  1. Circular Motion Created by Craig Smiley (Harrison HS, West Lafayette, IN) Supported by grant PHY-0851826 from the National Science Foundation and by Purdue University

  2. Uniform Circular Motion Demo: Tennis dodge-ball, penny & coat hanger, bucket of water & rope, circle path on floor

  3. Circular Motion You left a cup of coke on the top of your car, and somehow it stayed on until you made a left-hand turn. Which way would it travel when it falls off? A.  B.  C. ↑ D.

  4. Circular Motion You are riding on a merry-go-round and fell off (you didn’t jump nor were you pushed). Which way would your body travel before hitting the ground? A.  B. ↘ C. ↓ D.

  5. Circular Motion When you were younger, your uncle grabbed onto your hands and swung you around and around in a circle at a constant speed. What force(s) are acting on you? • A force acting in the direction of motion • A force acting radially inward • A force acting radially outward • Both A and B • Both A and C • A, B & C

  6. Circular Motion You are a passenger in a car and not wearing your seat belt. Without increasing or decreasing its speed, the car makes a sharp left turn, and you find yourself colliding with the right-hand door. What horizontal forces are acting on you? (ignore friction) • Before and after the collision, there is a rightward force pushing you into the door. • Starting at the time of collision, the door exerts a leftward force on you. • both of the above. • neither of the above.

  7. Circular Motion You’re in your car on an non-banked circular entrance ramp going onto the interstate making a hard right-hand turn while going pretty fast. What kind of force is acting on your car playing the role of centripetal force? • Gravity • Normal • Applied • Friction • It’s just centripetal force

  8. Circular Motion What is the correct FBD of your car when it is turning on a frictionless banked curve while moving fairly quickly around the curve looking at the back of the car? A. B. C. D. E. None of these

  9. Circular Motion If you are on a right-hand exit ramp going at a constant speed, what is the direction of your acceleration at this moment? • ← • ↑ • → • ↗ • There is not accel

  10. Circular Motion When turning on a banked curve what is the direction of the centripetal force? Follow up: How should you orientate the axis?

  11. Circular Motion What is the correct FBD of your car when it is turning on a banked curve while moving fairly quickly around the curve? A. B. C. D.

  12. Circular Motion You are spinning a tennis ball at the end of a string. If you increased the length of the string and but kept the speed at which the tennis ball was going the same, what would happen to the tension in the string? • Increase • Decrease • Stay the same

  13. Circular Motion You are spinning a tennis ball at the end of a string. If you triple the speed at which the tennis ball was going, but kept the length of the string the same, what would happen to the tension in the string? • Increase by x 9 • Increase by x 3 • Remain the same • Decrease by x 1/3 • Decrease by x 1/9

  14. Circular Motion You are spinning a tennis ball at the end of a string. If you doubled the length of the string and doubled the speed at which the tennis ball was going, what would happen to the tension in the string? • Increase • Decrease • Stay the same

  15. Circular Motion You are spinning a tennis ball at the end of a string. If you increased the tension in the string and kept length of the string the same, what would happen to the period of the tennis ball? • Increase • Decrease • Stay the same

  16. You are riding on a merry-go-round near the edge and moving at a certain speed. A friend tries to get on, and you move in towards the center to make room for him (1/4 the distance away from the center from where you were). The process of him getting on slows your speed by ½ of your original speed. What happened to your centripetal force? • Increased • Decreased • Stayed the same

  17. Non-Uniform Circular Motion Demos: Hotwheel loop, water in bucket, bridge swing video

  18. Vertical Circles You are driving over a hill at a constant speed. What is the direction that you should make positive if you want the acceleration of the car to be positive? • The way car is moving • In direction of Fg • Radially inward, towards center of circular path • Radially outward, away from center of circular path • There is no acceleration, so it doesn’t matter.

  19. Vertical Circles You are driving over a hill at a constant speed. What is the direction of the net force acting on the car at the top of the hill? • ↑ • → • ↓ • ↗ • ΣF = 0

  20. Vertical Circles You are driving over a hill at a constant speed. What is correct set-up for the forces acting on the car at the top of the hill? • Fg – FN = Fc • FN – Fg = Fc • FN – Fg = 0 • FN + Fg = Fc • None of these

  21. Vertical Circles As a hotwheel car goes quickly around a loop-a-loop, what is the FBD of the car at the highest point? (assume frictionless) A. B. C. D. E. None of these

  22. Vertical Circles A hotwheel car goes quickly around a loop-a-loop. When the car is at the highest point, the force set-up looks like: • Fg – FN = Fc • FN – Fg = Fc • FN – Fg = 0 • FN + Fg = Fc • None of these

  23. Vertical Circles Moving at the top of a loop, what is the apparent weight if the car is going the minimum speed needed to just go in a circular path around the loop? • FN = mg • FN = mv2/r – mg • FN = mg + mv2/r • FN = mv2/r E. FN = 0

  24. Vertical Circles Moving at the top of a loop, what is the apparent weight if the minimum speed needed to make the loop is exceeded? • FN = mg • FN = mg – mv2/r • FN = mg + mv2/r • FN = mv2/r E. FN = mv2/r – mg

  25. Vertical Circles What is the minimum speed needed at the top for a hotwheel car to make a loop that has a radius of 40cm? • 0 m/s • 1.5 m/s • 2 m/s • 7.5 m/s • 10 m/s

  26. Vertical Circles A boy is swinging on a tire swing. What is the force set-up when the child is at the lowest point? • Fg – FT = Fc • FT – Fg = Fc • FT – Fg = 0 • FT + Fg = Fc • None of these

  27. Vertical Circles A boy is swinging on a tire swing. When he is at the lowest point, which force is the greatest? • Fg • Fc • FT • FT = Fg • They are all the same

  28. Vertical Circles Moving at the bottom of a loop, what is the Normal force equal to? • FN = mg • FN = mg – mv2/r • FN = mg + mv2/r • FN = mv2/r • None of these

  29. Vertical Circles You are driving over a hill that has a radius of curvature of 40m. What is the maximum speed at which you can drive and still move along the road? • 10m/s • 20m/s • 60m/s • 200m/s • Not enough info given

  30. Circular Motion If you on an entrance ramp to the interstate speeding up while making a right-hand turn, what is the direction of your acceleration? • ← • ↑ • → • ↖ • ↗

  31. Vertical Circles What is the direction of the net force acting on the car that this point as it travels up vertical loop. • ↙ • ← • ↖ • ↑ • None of these

  32. At which location did the cart experience the greatest acceleration? E. All the same

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