2. Dynamics zWhy things move yAccelerations caused by Forces

3. Forces Non ContactContact PushesPullsGravitationalElectromagneticNuclear NormalFrictionTension M T f N W ElectricMagnetic perpendicular to surface

4. Labeling Forces What forces are acting on the yellow ball? F

5. Labeling Forces What forces are acting on the yellow ball? F by, on

6. Labeling Forces What forces are acting on the yellow ball? W by, on

7. Labeling Forces What forces are acting on the yellow ball? W Earth, Ball

8. Labeling Forces F by, on ANYTHING LESS IS AN INCOMPLETE ANSWER!!!

9. Sir Isaac Newton (1642-1727)

10. Newton’s Laws of Motion z1 st Law: no net force  no acceleration no acceleration  no change in motion Objects at rest will remain at rest and objects in motion will remain in motion at constant speed, in a straight line, unless acted on by a net force

11. Newton’s Laws of Motion z1 st Law: no net force  no acceleration no acceleration  no change in motion Objects at rest will remain at rest and objects in motion will remain in motion at constant speed, in a straight line, unless acted on by a net force

12. Mass zMeasure of how much ‘stuff’ zMeasure of how hard it is to speed up or slow down the object zMass and weight are very different

15. POP!

16. More net force - more acceleration (constant mass) F a F a  aF net

17. More mass - less acceleration (constant net force) F a a F  a M 1

18. Putting it all together a  M F net Constant * Newton is defined such that constant = 1.  a M F net  aM Newton’s 2 nd Law

19. Newton’s Laws z1 st yObjects at rest will stay at rest and objects in motion will stay in motion, at a constant speed, in a straight line, unless acted on by a net force. z2 nd  Objects with a non-zero net force accelerate in the direction of the net force via F net = ma

20. THE BRICK OF DEATH!!! I Physics

21. What THING is pushing on the rocket? Is this a contact or non-contact force?

22. Poor Gary: Gary has a major problem. After studying Newton’s Third Law in his physics class, he has convinced himself of its validity. Unfortunately, he has convinced himself while sitting in a closed room with a single door. He reasons to himself: “If I push on the door to go out, Newton’s 3rd Law tells me that the door is going to push back with an equal force. That force is going to cancel the force that I push with. Even if I push as hard as I can, that door is going to push back just as hard! Oh no! I’m stuck in this room! Why did I ever take physics!”

23. The famous bug problem: A bug splats on the windshield of a car moving at 100 mph. Which feels the greater force, the car or the bug? Which has the worst day?

24. W EP N SP person N FS W ES N PS scale Apparent Weight True Weight Newton’s 3 rd Law and the Scale

25. Apparent weight measured as the reading of the scale equal to the normal force of the scale on your feet equal to weight for a=0

26. Elevator W EP N SP v = constant a = 0 Apparent Weight True Weight

27. Elevator W EP N SP a is upward a Apparent Weight True Weight

28. Elevator W EP N SP a is downward a Apparent Weight True Weight

29. Elevator W EP N SP How large should the normal force be? a =9.8 m/s/s down g

30. Elevator W EP a =9.8 m/s/s down How large should the normal force be? g Weightless?? Apparently

31. The weightlessness of space!

32. What’s his mass? 80 kg

33. What’s his weight? 648 N ! What ?

34. Apollo 17 Earth as seen from the Moon

35. What is the correct orbit of the space shuttle?

38. a = 8.1 m/s 2

39. Orbit z“…there is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss.” –Douglas Adams Life, The Universe, and Everything

41. Circular motion Which direction is the instantaneous velocity?

42. Uniform Circular motion Which direction is the instantaneous velocity? Which direction is the acceleration?

43. Uniform Circular motion W E,B T S,B Freebody Which direction is the instantaneous velocity? Which direction is the acceleration?

44. Uniform Circular motion Which direction is the instantaneous velocity? Which direction is the acceleration? W E,B T S,B Freebody

45. Uniform Circular motion Which direction is the instantaneous velocity? Which direction is the acceleration? Freebody Aren’t we missing something? TyTy W E,B TxTx

46. THE CENTRIFUGAL FORCE!  Centrifugal. adj. Moving or directed away from the center. TyTy W E,B TxTx

47. THE CENTRIFUGAL FORCE! CENSORED  Centrifugal. adj. Moving or directed away from the center. TyTy W E,B TxTx CENSORED

48. Forces Non ContactContact PushesPullsGravitationalElectromagneticNuclear NormalFrictionTension M T f N W ElectricMagnetic perpendicular to surface

49. TyTy W E,B TxTx THE CENTRIFUGAL FORCE! CENSORED  Centrifugal. adj. Moving or directed away from the center. zThe centri*&%#l force DOES NOT EXIST! zFor uniform circular motion the net force must be towards the center of the circle. zTherefore: The acceleration is ‘center seeking’ CENSORED

50. TyTy W E,B TxTx THE CENTRIFUGAL FORCE! CENSORED  Centrifugal. adj. Moving or directed away from the center. zThe centri*&%#l force DOES NOT EXIST! zFor uniform circular motion the net force must be towards the center of the circle. zTherefore: The acceleration is centripetal CENSORED

51. The swinging bucket of death A B C I Physics Draw freebody diagrams for the water at points A, B, and C.

52. Centripetal Acceleration zFor U.C.M. there must be a centripetal net force

53. Centripetal Acceleration zFor U.C.M. there must be a centripetal net force  centripetal acceleration