2. Rotational Motion

3. Uniform Circular Motion 2 Conditions: Uniform speed Circle has a constant radius. Caused by acceleration!

4. Centrifugal Force Not Real! The “force” is actually inertia

5. When a car accelerates You, as a passenger, feel as if you are flung backward. Your inertia (mass) resists acceleration. You are NOT flung backward. Your body wants to remain at rest as the car accelerates forward.

6. When a car decelerates You, as a passenger, feel as if you are flung forward. Your inertia (mass) resists the negative acceleration. You are NOT flung forward. Your body wants to remain in motion at constant velocity as the car accelerates backwards.

7. When a car turns You feel as if you are flung to the outside. Your inertia resists acceleration. You are not flung out, your body simply wants to keep moving in straight line motion!

8. Centripetal Acceleration: Acceleration responsible for uniform circular motion.

9. Centripetal Acceleration ALWAYS points toward the center of the circle. NEVER changes an object’s speed. ALWAYS changes the object’s direction. ALWAYS perpendicular to the velocity. v acac v acac acac v Centripetal Acceleration Bugs

10. Centripetal Acceleration a c = v t 2 /r a c : centripetal acceleration in m/s 2 v: tangential speed in m/s r: radius in meters

11. Concept Check: An object moves in a circular path with a constant speed. a. Is the objects velocity constant? No, direction of v is changing b. Is its a c constant? No, direction of a c is changing

12. Centripetal Force: Force responsible for uniform circular motion. FcFc v FcFc FcFc v Always toward center of circle! NASA on Centripetal Force v

13. Centripetal Force F c = m a c F c = m v t 2 / r F c : centripetal force in N v: tangential speed in m/s r: radius in meters

14. Cause of Centripetal Force Centripetal force is not a new type of force. You can always identify the real force which is causing the centripetal acceleration. Nearly any kind of force can act as a centripetal force.

15. Friction as F c As a car makes a turn, the force of friction acting upon the turned wheels of the car provide the centripetal force required for circular motion.

16. Tension as F c As a bucket of water is tied to a string and spun in a circle, the force of tension acting upon the bucket provides the centripetal force required for circular motion.

17. Gravity as F c As the moon orbits the Earth, the force of gravity acting upon the moon provides the centripetal force required for circular motion.

18. Normal Force as F c Centripetal force when you are upside down arises from a combination of normal force and gravity.

19. Weight on a string moving in vertical circle Centripetal force arises from combination of tension and gravity. Must have a large velocity to accomplish this

20. If a hobo steals your truck keys and does donuts in the Wal-Mart parking lot, what is the centripetal force? The frictional force that exists between your tires and the ground while turning causes the truck to maintain the circular motion necessary to generate a donut. Could the hobo do donuts in a hockey rink if he stole a zomboni?