1. Force and Motion-II: continued Friction and Drag;Circular Motion Lecture 6 Monday:2 February 2004

9. UNIFORM CIRCULAR MOTION

10. CIRCULAR MOTION When an object travels in a circle, its velocity is constantly changing (in direction-at least). That means the object has a non-zero acceleration even if it moves at constant speed.

11. What is the direction of this acceleration?

12. Acceleration in Circular Motion Centripetal acceleration: Direction: Toward the center of the circle Magnitude:

13. FORCES IN CIRCULAR MOTION An “unbalanced” force must cause the acceleration.

14. Using Freebody Diagrams to Analyze Forces Twirl a ball attached to a string in a vertical circle. What forces act on the ball and what are the direction of these forces?

15. Using Freebody Diagrams to Analyze Forces What forces act on the ball and what are the direction of these forces? Top Bottom T T W W a a Are we missing a force? (the centripetal force)? Is the acceleration =g?

16. Using Freebody Diagrams to Analyze Forces What forces act on the ball and what are the direction of these forces? Top Bottom T T W W a a Are we missing a force? (the centripetal force)? Is the acceleration =g? -T-W=m(-a) or T+W=ma T-W=ma

17. Any force can be a “centripetal” force. -Gravitational Attraction -Tension in a string -Normal Force -A push or pull… Does the planet in orbit here have a gravitational force AND a centripetal force acting on it?

18. PERIOD IN CIRCULAR MOTION