2. Chapter machines

3. Machines A device used to multiply forces or simply to change the direction of forces

4. Components of Machines Lever …a bar that is free to pivot, or turn, about a fixed point Fulcrum….Fixed point of the Lever Effort Arm….Part of lever on which the effort force is applied Resistance arm…. Part of the lever that exerts the resistance force

5. Type I or First Class Lever The fulcrum between the force and the load, or between input and output.

6. Type II or Second Class Lever Reverse the position of the load and the fulcrum. The load is in between the fulcrum and the effort force.

7. Type III or Third Class Lever Fulcrum is at one end the load is at the other end….Input force is applied between them

8. Machines Fulcrum Mg Work = F D = N d D d M N F

9. Pulley A Kind of a lever that can be used to change the direction of a force.

10. Mechanical advantage The ratio of resistance force to effort force MA = F r /F e F e ….effort force F r …..resistance force

11. Ideal Mechanical advantage Workout = Workin F r d r = F e d e IMA = d e /d r

12. Efficiency Workout = Workin efficiency = w o / W i X 100 %

13. Compound Machines Consists of two or more simple machines linked….. so that the resistance force of one machine……… becomes the effort force of the second.

14. Rube-Goldberg

15. Machines - An Application of Energy Conservation If there is no mechanical energy losses then for a simple machine... work input = work output ( F d )input = ( F d )output Examples - levers and tire jacks

16. Efficiency Useful energy becomes wasted energy with inefficiency. Heat is the graveyard of useful energy.

17. Comparison of Kinetic Energy and Momentum Kinetic energy is a scalar quantity. Momentum is a vector quantity. Discuss rubber bullets as compared to lead bullets.

18. Example Questions A 10 lb weight is lifted 5 ft. A 20 lb weight is lifted 2.5 ft. Which lifting required the most work? (a) 10 lb weight (b) 20 lb weight (c) same work for each lifting (d) not enough information is given to work the problem (c) same work for each lifting

19. An object of mass 6 kg is traveling at a velocity of 30 m/s. How much total work was required to obtain this velocity starting from a position of rest? (a) 180 Joules (b) 2700 Joules (c) 36 Joules (d) 5 Joules (e) 180 N (b) 2700 Joules

20. A 20 Newton weight is lifted 4 meters. The change in potential energy of the weight in Newton. meters is (a) 20 (b) 24 (c) 16 (d) 80 (e) 5 (d) 80