1. Classical Mechanics Friction: Examples Work &Kinetic Energy
Midterm 2 will be held on March 13. Covers units 4-9
Classical Mechanics Friction: Examples Work &Kinetic Energy
Discussion Sections
Wednesdays 3-4PM
Thursdays 2-3 PM
Fridays 3-4PM
JFB B-1
NS 203 ?
Janvida
Cassie
Wayne
Help Lab Schedule
Thursdays 9AM-1:30 PM
Thursdays 3:15 - 4PM

2. Schedule

3. Schedule

4. Accelerating Blocks

5. Accelerating Blocks

6. Carnival Ride

7. Carnival Ride x x

8. Accelerating Truck

9. Accelerating Truck

10. Mass on Incline

11. Mass on Incline

12. Mass on Incline

13. Mass on Incline 2

14. Mass on Incline 2

15. Mass on Incline 2

16. Mass on Incline 2

17. Classical Mechanics Lecture 7
Midterm 2 will be held on March 13. Covers units 4-9
Classical Mechanics Lecture 7
Today’s Concepts:
Work & Kinetic Energy

18. Lecture Thoughts

19. Kinetic Energy and Work

20. Work-Kinetic Energy Theorem
The work done by force F as it acts on an object that moves between positions r1 and r2 is equal to the change in the object’s kinetic energy:

22. What about Potential Energy??….next Unit!

23. Work-Kinetic Energy Theorem
The work done by force F as it acts on an object that moves between positions r1 and r2 is equal to the change in the object’s kinetic energy:
But again…!!!

25. Newton’s 2nd law Work & Kinetic Energy

28. Vector Multiplication

29. The Dot Product

30. The Dot Product

31. The Dot Product

32. Work –Kinetic Energy Theorem: Work on sliding box
Forces that act perpendicular to displacement perform no work!!!

33. Work –Kinetic Energy Theorem

34. Work done by Weight

35. Work –Kinetic Energy Theorem Applied

37. Work done by a Spring
On the last page we calculated the work done by a constant force when the orientation of the path relative to the force was changing. On this page we will calculate the work done by a spring in one dimension. In this case the orientation of the path relative to the force is simple, but the magnitude of the force changes as we move.
If the coordinate system is chosen such that x=0 is the relaxed length of the spring as shown, then the force exerted by the spring on some object attached to its end as function of position is given by Hookes law [F = -kx]. As we move the object between two positions x1 and x2, the force on the object clearly changes. Breaking the movement into tiny steps we see that the work done by the spring along each step will depend on the position : [dW = F(x)*dx = -kxdx]. To find the total work done we need to integrate this expression between x1 and x2 [show].
The mathematics of doing this is straightforward, but its very important to realize what it means conceptually. Evaluating a one dimensional integral of some function F(x) between two points x1 and x2 is really just finding the area under the curve between these points [show] . Evaluating the above integral to find the work done is therefore just finding the area under the force versus position plot between the points x1 and x2. [show]
Notice that the formula for the work done by a spring that we just derived depends only on the endpoints of the motion x1 and x2, hence we see that this is a conservative force also. 37

38. Main Points

39. Main Points

40. Main Points