1. Circular Motion

2. Which horse on a merry-go-round moves faster… One on the outside rail One near the inside rail?

3. Or…how about a turntable?

4. More than one kind of speed… Linear speed (velocity)  Distance  time  Greater for outside horse  AKA tangential speed Rotational speed (velocity)  # of rotations per unit of time  Same for all horses  AKA angular speed

5. Interesting application… Rims of train wheels are tapered

6. Washer on a string… The washer’s speed does not change, but its velocity does  Centripetal acceleration

7. What would Isaac say? Newton’s 1 st Law Newton’s 2 nd Law  Force needed to cause an acceleration

8. A new force… Centripetal force – force that causes an object to follow a circular path

9. What’s wrong with this picture?

10. Be careful… Centripetal force sometimes called “centrifugal” force  A “fictitious” force

11. Centripetal Acceleration a c = v 2 /r

12. Circular Motion Problems #1 a - d

13. Back to Isaac... F = ma F c = m (v 2 /r) F c = mv 2 r

14. Circular Motion Practice #1 e #2

15. Centripetal Force Lab

16. Fill in the blank… A ____________ causes acceleration. A ____________ causes rotation. force torque

17. Let’s pretend... You need to loosen a stuck bolt with a wrench... You aren’t strong enough...what do you do?

18. When opening a door... Is it easier to open if you push close to or far away from the hinges?

19. Torque Produces rotation   = Fr  Long arm, less force  More force, shorter arm Ex. wrench, screwdriver, doorknob

20. Circular Motion Practice #3

21. Rotational Inertia Resistance to change in rotational motion Greater distance from center of mass to rotation point = greater inertia

22. Why do baseball players “choke up” on the bat?  “ Choking up” on a baseball bat will increase speed of swing

23. Why do giraffes have a slower gait than Chihuahuas?

24. Why do longer pendulums swing more slowly than shorter ones?

25. Angular Momentum mvr Ice skater pulls in arms – r decreases Momentum is conserved mvr = mvr

26. Quiz Next Class!