PHY 113 C General Physics I 11 AM – 12:15 P M MWF Olin 101 Plan for Lecture 10

1. PHY 113 C General Physics I • 11 AM – 12:15 PM MWF Olin 101 • Plan for Lecture 10 • Chapter 9 -- Linear momentum • Impulse and momentum • Conservation of linear momentum • Examples – collision analysis • Notion of center of mass PHY 113 C Fall 2013 -- Lecture 10

2. PHY 113 C Fall 2013 -- Lecture 10

3. Summary of physics “laws” PHY 113 C Fall 2013 -- Lecture 10

4. Another way to look at Newton’s second law: • iclicker question: • Why would you want to define linear momentum? • To impress your friends. • To exercise your brain. • It might be helpful. • To distinguish it from angular momentum. PHY 113 C Fall 2013 -- Lecture 10

5. Relationship between Newton’s second law and linear momentum: (if m is constant) PHY 113 C Fall 2013 -- Lecture 10

6. PHY 113 C Fall 2013 -- Lecture 10

7. Suppose that a tennis ball with mass m=0.057 kg approaches a tennis racket at a speed of 45m/s. What is the impulse the racket must exert on the ball to return the ball in the opposite direction at the same speed. Assume that the motion is completely horizontal. PHY 113 C Fall 2013 -- Lecture 10

8. Example: A 1500 kg car collides with a wall, with vi= -15m/s and vf=2.6m/s. What is the impulse exerted on the car? PHY 113 C Fall 2013 -- Lecture 10

9. Example of graphical representation of F(t) PHY 113 C Fall 2013 -- Lecture 10

10. Physics of composite systems PHY 113 C Fall 2013 -- Lecture 10

11. Example – completely inelastic collision; balls moving on a frictionless surface PHY 113 C Fall 2013 -- Lecture 10

12. Energy loss in this example: PHY 113 C Fall 2013 -- Lecture 10

13. Example – completely elastic collision; balls moving on a frictionless surface PHY 113 C Fall 2013 -- Lecture 10

14. Completely elastic collision; numerical example: PHY 113 C Fall 2013 -- Lecture 10

15. iclicker exercise: • We have assumed that there is no net force acting on the system. What happens if there are interaction forces between the particles? • Analysis still applies • Analysis must be modified PHY 113 C Fall 2013 -- Lecture 10

16. Example from homework: PHY 113 C Fall 2013 -- Lecture 10

17. Example from homework: -- continued • iclicker question • Do you expect Kf-Ki to be • >0 • <0 PHY 113 C Fall 2013 -- Lecture 10

18. Another example: before vf after PHY 113 C Fall 2013 -- Lecture 10

19. Examples of two-dimensional collision; balls moving on a frictionless surface PHY 113 C Fall 2013 -- Lecture 10

20. Examples of two-dimensional collision; balls moving on a frictionless surface PHY 113 C Fall 2013 -- Lecture 10

21. Example: two-dimensional totally inelastic collision m1=1500kg m2=2500kg PHY 113 C Fall 2013 -- Lecture 10

22. iclicker exercise: • Can this analysis be used to analyze a real collision? • Of course! The laws of physics must be obeyed. • Of course NOT! In physics class we only deal with idealized situations which never happen. PHY 113 C Fall 2013 -- Lecture 10

23. Another example of 2-dimensional elastic collision: vf m vi m PHY 113 C Fall 2013 -- Lecture 10

24. Energy analysis of a simple nuclear reaction : Q=4.87 MeV PHY 113 C Fall 2013 -- Lecture 10

25. Energy analysis of a simple reaction : Q=4.87 MeV PHY 113 C Fall 2013 -- Lecture 10

26. Elastic collision in two dimensions PHY 113 C Fall 2013 -- Lecture 10

27. Elastic collision in two dimensions -- example of elastic proton-proton scattering PHY 113 C Fall 2013 -- Lecture 10

28. Elastic collision in two dimensions -- example of elastic proton-proton scattering PHY 113 C Fall 2013 -- Lecture 10

29. The notion of the center of mass and the physics of composite systems PHY 113 C Fall 2013 -- Lecture 10

30. PHY 113 C Fall 2013 -- Lecture 10

31. Finding the center of mass PHY 113 C Fall 2013 -- Lecture 10

32. Example from webassign : y m1 m2 m3 m4 x PHY 113 C Fall 2013 -- Lecture 10

33. Finding the center of mass • For a solid object composed of constant density material, the center of mass is located at the center of the object. PHY 113 C Fall 2013 -- Lecture 10