1. Chapter 8: Conservation of Energy & Simple Machines

2. Conservation of Energy
Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.

3. A little Review

4. Try these questions.

5. The answers
A: PE = 40 J (since the same mass is elevated to 4/5-ths height of the top stair)
B: PE = 30 J (since the same mass is elevated to 3/5-ths height of the top stair)
C: PE = 20 J (since the same mass is elevated to 2/5-ths height of the top stair)
D: PE = 10 J (since the same mass is elevated to 1/5-ths height of the top stair)
E and F: PE = 0 J (since the same mass is at the same zero height position as shown for the bottom stair).

6. Practice Problem

7. Work Input = Work Output
Machine: A device used to multiply forces or simply to change the direction of forces.
Work Input = Work Output
Fd = fd

8. Simple Machines

9. Mechanical Advantage: The ratio of output force to the input force of a machine.

10. A machine lifts a 575 N mass, but the person using the machine
only exerts 25 N. What is the mechanical advantage of
the machine?

11. A lever is used to lift a load weighing 300 N
A lever is used to lift a load weighing 300 N. The force needed was 600 N. What is the mechanical advantage of this first class lever?

12. Lever: A bar that turns around a fixed point(fulcrum). 3 types

13. Class 1 lever •M.A. = 1, when Load arm = Effort arm, e.g. beam balance
Relative positions of load, fulcrum and effort of class I lever
•M.A. = 1,
when Load arm = Effort arm, e.g. beam balance
•M.A. > 1,
when Effort arm > Load arm, e.g. Cutting pliers
•M.A. < 1,
when Effort arm < Load arm, e.g. Garden scissors

14. Class 2 lever MA is always greater than 1 Force multiplier
effort arm is always greater than the load arm

15. Class 3 lever MA always less than 1
Gain speed, larger movement of load

16. Pulley: A lever that can change the direction of a force.
MA is determined by the strands the support the load.

17. Efficiency: The ratio of useful work output to total work input.

18. A machine requires an put of 600 J of energy to lift a 25 N box into the air a distance of 4 meters. Calculate the efficiency of the machine.

19. A machine operates with an efficiency of 65 %
A machine operates with an efficiency of 65 %. How much energy would the machine require if the machine was to lift a 3 kg box into the air 20 m?