1. Circular Motion
Q: What makes you dizzy on a rollercoaster ride?

2. Uniform Circular Motion
Uniform circular motion is motion along a circular path in which there is no change in speed, only a change in direction.
Velocity v tangent to path. v Fc
Centripetal force Fc toward center.
Q: What is the direction
of acceleration?
ac is directed toward center.

3. Uniform Circular Motion
1. Is there an outward force acting on the ball?
No, the so called centrifugal force does not exist.
2. How does the ball move if the string breaks?
Ball moves along the tangent to path, NOT outward as might be expected. v
When centripetal force Fc is removed, ball continues in straight line.
Centripetal force Fc is needed to change direction.

4. A Car on an Exit
You are sitting on the seat next to the outside door. What is the direction of the resultant force on you as you turn? Is it away from center or toward center of the turn? Fc
Car going around a curve.
Force ON you is toward the center.

5. A Car on an Exit (continued)
The centripetal force is exerted BY the door ON you. (Centrally) F’
Reaction Fc
There is an outward force, but it does not act ON you. It is the reaction force exerted BY you ON the door. It affects only the door.

6. “Gravitron” at the Fair
Disappearing platform at fair. r Fc
What exerts the centripetal force in this example and on what does it act?
The centripetal force is exerted BY the wall ON the man. It is the normal force. A reaction force is exerted by the man on the wall, but that does not determine the motion of the man. It acts on the wall.

7. Spin Cycle on a Washer
How is the water removed from clothes during the spin cycle of a washer?
Does the centripetal force throw water off the clothes?
NO. Actually, it is the LACK of a force that allows the water to leave the clothes through holes in the circular wall of the rotating washer.