1. Circular Motion
Chapter 7, Section 3

2. Motion in a Circle
Revolution: If entire object is moving in a circle around an external point. The earth revolves around the sun once a year
Rotation: Axis of rotation is internal and passes through object. The earth rotates on its axis once a day

3. Uniform Circular Motion
Object moving in a circle at a constant speed and constant radius
Even though speed is constant, object is accelerating because direction of motion is constantly changing

4. Velocity in Circular Motion
At any moment, instan-taneous velocity is directed perpendicular to radius of circle
Called tangential velocity because it is tangent to circle

5. Angular Velocity or Speed
Number of revolutions or rotations per unit of time.
All parts of rotating object will have same rotational (angular) speed
Common unit is revolutions per minute (rpm); fundamental unit is radians/second

6. Centripetal Acceleration
Centripetal means “center-seeking”
Velocity vector is directed tangent to circular path and is constantly changing direction
Change in velocity caused by force towards center, creating acceleration towards center of circle

7. Centripetal Acceleration
Directly proportional to linear speed squared.
Inversely proportional to radius of circle for the same linear speed.

8. Centripetal Force
Force needed to cause an object to follow circular path.
Always directed toward center of circle
Always perpendicular to velocity
Can be caused by tension in string, friction, gravity, electrical or magnetic force.

9. Centripetal Force
Example: car turning a corner has centripetal force from friction between tires and road.
If road is icy, not enough friction to provide cent. force and car skids
Other examples: washing machine, centrifuge, carnival rides.

10. Circular Motion Equations
Centripetal Force:
Centripetal Acceleration:

11. Centrifugal force Not an actual force means “center-fleeing”
Is actually caused by inertia
Seems like a force in a turning reference frame
Reference frame: objects around you that appear to be stationary

12. Centrifugal Force
Example: In a car turning a sharp corner, you feel a force pressing you against the opposite side of the car.
Car is actually providing centripetal force causing you to turn with it.
From outside reference frame, centrifugal force does not exist.

13. Vocabulary Centripetal Centrifugal Rotation Revolution Linear speed
Rotational speed
Reference frame

14. Summary Rotation is motion about internal axis
Revolution is motion about external axis
Centripetal force pulls object toward center of circle, causes centripetal acceleration
There is no force pushing outward
Inside rotating reference frame, centrifugal force seems present; can simulate gravity