1. Universal Gravitation & Universal Circular Motion Review Questions Divided by Category

2. Definitions What is the direction of the centripetal force at this point? It is spinning clockwise.

3. Definitions - Answer What is the direction of the centripetal force at this point? It is spinning clockwise. “centripetal force” – is a “center pointing” force. It is always directed towards the inside of the circle. It doesn’t matter which way the circle is spinning.

4. Definitions What is the centripetal force for an angry bird spinning on a string?

5. Definitions - Answer What is the centripetal force for an angry bird spinning on a string? Tension Force The tension force of the rope pulls on the bird, keeping it from flying off of the string.

6. Definitions What is the centripetal force that keeps the moons of Mars orbiting around Mars?

7. Definitions - Answers What is the centripetal force that keeps the moons of Mars orbiting around Mars? Force of Gravity For objects in space, the force of gravity pulls on the object, keeping it from flying away. It is a center pointing force.

8. Definitions What is the direction of the tangential velocity at this point? It is spinning clockwise.

9. Definitions - Answers What is the direction of the tangential velocity at this point? It is spinning clockwise. The direction of tangential velocity is always tangent to the circle at that point. It is the direction the object will fly off at if the centripetal force is suddenly released.

10. Definitions When an object is moving at a constant speed in a circle, is there acceleration? If so, what value does that acceleration change?

11. Definitions – Answers When an object is moving at a constant speed in a circle, is there acceleration? If so, what value does that acceleration change? Yes, there is always centripetal acceleration if an object is moving in a circle. The direction changes – you need acceleration to change direction.

12. Definitions What is the name for the apparent force experienced by a person rotating in a circular reference frame?

13. Definitions - Answers What is the name for the apparent force experienced by a person rotating in a circular reference frame? Centrifugal force. – This is not a “real” force – It means “center-fleeing”, and points away from the center.

14. Definitions What is the term for the amount of time it takes to complete one rotation in circular motion?

15. Definitions - Answers What is the term for the amount of time it takes to complete one rotation in circular motion? Period – One period is the time it takes to make a single rotation. – It is calculated by dividing seconds by the number of rotations

16. Gravity Relationships If the moon doubled its distance from the earth, what would happen to the pull of the moon’s gravity on the earth?

17. Gravity Relationships - Answers If the moon doubled its distance from the earth, what would happen to the pull of the moon’s gravity on the earth? It would decrease by a factor of 4. (x ¼) – The distance was increased by a factor of 2 (x2) – Distance and Force of gravity have an inverse squared relationship so… 2 squared = 4. Inverse = decrease or x 1/4

18. Gravity Relationships The earth has a mass 6x10^22 times greater than yourself. When the earth pulls you down with a force of 980N with what force do you pull up on the earth?

19. Gravity Relationships - Answers The earth has a mass 6x10^22 times greater than yourself. When the earth pulls you down with a force of 980N with what force do you pull up on the earth? Answer: 980 N up. The force you exert on the earth is the same as the force the earth exerts on you.

20. Gravity Relationships If the mass and radius of the earth doubled, what would happen to your weight?

21. Gravity Relationships - Answer If the mass and radius of the earth doubled, what would happen to your weight? Weight would decrease by a factor of 2 (x ½) – Weight is your force of gravity (Fg) Mass increased by a factor of 2. (x2) Distance increased by a factor of 2. Mass has a direct relationship with Fg. Distance has an inverse squared relationship with Fg. Fg was increased by a factor of 2 (x2) Fg was decreased by a factor of 4 (x1/4) Fg decreased by a factor of 2 (x2, x ¼)

22. Circular Relationships If you want to travel as fast as possible on a merry go round, where should you sit?

23. Circular Relationships - Answer If you want to travel as fast as possible on a merry go round, where should you sit? Answer: On the outside. The amount of time it takes to make one rotation is the same wherever you are on the merry-go-round. The closer you are to the center, the less distance you have to travel, so your speed is faster near the outside (as your radius increases).

24. Circular Relationships When moving clockwise in a circle, draw the direction of your acceleration and the direction of your velocity at the given point.

25. Circular Relationships - Answer When moving clockwise in a circle, draw the direction of your acceleration and the direction of your velocity at the given point. In circular motion, acceleration and velocity are perpendicular. velocity acceleration

26. Circular Relationship If you double your radius, what will happen to your centripetal acceleration?

27. Circular Relationship - Answer If you double your radius, what will happen to your centripetal acceleration? Your centripetal acceleration will decrease by a factor of 2 (x1/2) Radius and acceleration have an inverse proportional relationship. If radius increases by a factor of 2 (x2), then acceleration will decrease by that same factor (x1/2).

28. Circular Relationship If you triple your radius, but maintain the same velocity, what happens to your period of rotation?

29. Circular Relationship - Answers If you triple your radius, but maintain the same velocity, what happens to your period of rotation? Your period of rotation triples as well. – If you have more distance to travel, but you go the same speed, it will take more time to go that distance. – Radius and period are directly proportional. – V= (2πr)/T((2πr) = Circumference, T= period)

30. Circular Calculations If your tangential velocity is 15 m/s around a 30 m radius, what is the centripetal force acting on you if you have a mass of 70 kg?

31. Circular Calculations - Answer If your tangential velocity is 15 m/s around a 30 m radius, what is the centripetal force acting on you if you have a mass of 70 kg? 525 Newtons You use 2 formulas for this problem.

32. Circular Calculations If a record spins 100 times in 60 seconds, what is its period?

33. Circular Calculations - Answers If a record spins 100 times in 60 seconds, what is its period? Period =.6 seconds Period is time/rotations, so 60/100 =.6 seconds.

34. Circular Calculations What is the velocity of a rollerderby player that loops around a track with a 7 meter radius in 12 seconds?

35. Circular Calculations - Answers What is the velocity of a rollerderby player that loops around a track with a 7 meter radius in 12 seconds? 3.66 m/s You need to find the circumference of the track, and divide it by the time to travel the track.

36. Gravity Calculations The mass of the earth is 6x10^24 kg. What is the force of gravity between the sun and earth if the sun has a mass of 2x10^30 kg and the distance between them is 1.5 x 10^11 m?

37. Gravity Calculations - Answer The mass of the earth is 6x10^24 kg. What is the force of gravity between the sun and earth if the sun has a mass of 2x10^30 kg and the distance between them is 1.5 x 10^11 m?

38. Gravity Calculations If a rollercoaster makes a person accelerate at 27 m/s^2, how many g’s do they experience?

39. Gravity Calculations - Answers If a rollercoaster makes a person accelerate at 27 m/s^2, how many g’s do they experience? 2.75 g’s “g” is the acceleration of gravity = 9.8 m/s^2 To find the number of “g’s” just divide your acceleration by 9.8 27/9.8 = 2.75

40. Gravity Calculations What is the force of gravity between two objects with a mass of 35 kg and 100 kg, if they are 2 meters apart?

41. Gravity Calculations - Answers What is the force of gravity between two objects with a mass of 35 kg and 100 kg, if they are 2 meters apart?