1. Chapter 10
Circular Motion

2. 1. CIRCULAR MOTION Which parts on a merry-go-round move fastest?
Which have greater rotational speeds?
Examples of rotational motion:
Earth rotates and revolves
Rotation: AKA Spin – Object moves around an internal axis. (Earth rotates around polar axis)
Revolution: AKA Orbit – Object moves around an external axis. (Earth revolves around the sun)

3. Types of Speed Linear Speed = Distance/Time
Tangential Speed = Speed of something moving along a circular path
Rotational Speed = Number of Rotations/Time
Note that Tangential Speed depends on the rotational speed and the distance from the axis (One complete revolution covers a distance of 2πR).

4. Simple & Complex Objects
Motion of simple objects: Position
Motion of complex objects: Position & Rotation
Axis of
Rotation
SIMPLE
COMPLEX
Notice that the center of mass of the complex object follows the same path as the simple object
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5. Check Yourself 1 2 A pair of wheels are connected by a chain.
Which wheel has higher
rotational speed?
By how much?
Faster tangential speed on rim? 1 2
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6. Bicycles
Notice how gears work on a modern bicycle
SLOW
FAST
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7. Different Tangential Speeds
Circular Motion
Rotational Speed: Revolutions per second Tangential Speed: Total distance per second
Same Rotational Speed
Different Tangential Speeds
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8. 5. CENTRIPETAL FORCE Centripetal force - center seeking force
Examples: tin can and string, sling, moon and earth, car on circular path
Demo – Water in a Bucket
Demo - Loop the Loop

9. 6. CENTRIFUGAL FORCE Centrifugal force - center fleeing force
Often confused with centripetal
Examples: sling and bug in can
Centrifugal force is attributed to inertia.
Notice that an umbalanced force is needed to make an object travel in a circular path (centripetal)

10. CENTRIFUGAL FORCE IN A ROTATING REFERENCE FRAME
A frame of reference can influence our view of nature.
For example: we observe a centrifugal force in a rotating frame of reference, yet it is a fictitious (pseudo) force.
Centrifugal force stands alone (there is no action-reaction pair) - it is a fictitious force.

11. 8. SIMULATED GRAVITY
To get a = g, the proper rotation rate and the proper radius must be determined.
Rotational Force = mv2/r, so a = v2/r = 9.8 m/sec2
Gravity gradients in a rotating spacecraft
Jogging in space

12. Chapter 10 Review Questions

13. In walking, people normally bend their knees. Why?
(a) it is easier to swing their legs because bending lowers the rotational inertia of their legs
(b) it is easier to swing their legs because bending increases the rotational inertia of their legs

14. Which of the following forces is a pseudo force?
(a) tension in a rope (b) force of gravity (c) centripetal (d) friction (e) centrifugal