1. MACHINES and EFFICIENCY
Chapter

2. Key Terms Mechanical Advantage (MA) Ideal Mechanical Advantage (IMA)
A unitless ratio that indicates the number of times a machine multiplies your input force
Ideal Mechanical Advantage (IMA)
The calculated MA, does not consider friction
Actual Mechanical Advantage (AMA)
The measured or real MA, does consider friction
Because of friction, AMA < IMA

3. Key Terms Work = Force x distance Simple machine Compound machine
a device used to multiply forces or change the direction of forces
Compound machine
A machine composed of two or more simple machines

4. Key Terms Efficiency of a machine decreases as friction increases
Friction increases the thermal energy by increasing molecular KE (non-mechanical energy)
In other words… friction causes the particles to speed up, raising the average KE of the particles (and temperature!)
Friction causes the useful work output to be less than the total work input

5. Key Terms Input (effort) Output (resistance)
Input distance: the distance you input the force when using a machine
Input force: the force you use when using a machine
Output (resistance)
Output distance: the distance the object that work is done on moves
Output force: the force required to move the object without a machine (usually the weight of the object in newtons)

6. A simple machine Multiplies and redirects force
Does not reduce the amount of work to be done, but makes work easier.
MA > 1 means that your input force will be less than your output force (easier to do the work!)
More leverage means more mechanical advantage
If you increase MA, then
Input force will decrease
Input distance will increase

7. Key Terms Efficiency (a ratio)
Measures the “wastefulness” of the transfer of energy
More friction causes less efficiency
Efficiency is calculated using the following equations:
Actual mechanical advantage/idealized mechanical advantage
Useful work output/total work input

8. Key Terms When using a machine…
Work is done to move the object
Work is done against friction
Useful work output is the work done to move the object
Total work input is work done to move object + work done against friction

9. Simple Machines Lever Inclined plane Two families --Lever --Pulley
--Wheel and axle
--Ramp
--Wedge
--Screw

10. LEVER FAMILY

11. The Lever
fulcrum

12. Three Classes of Levers
First class
Examples:
Crowbar
See-saw

13. Three Classes of Lever
Second class
Examples:
Wheelbarrow
Door

14. Three Classes of Lever
Third class
Examples:
Human arm
Baseball bat

15. Calculating the Mechanical Advantage of a Lever
MA = input distance/output distance which is… MA = length of effort arm/length of resistance arm.
Effort or input distance
Resistance or output distance
0.5 m
2.5 m
Resistance arm
Effort arm

16. Calculating the Mechanical Advantage of a Lever
2nd class lever
3rd class lever
2nd class levers decrease the input force but increase the input distance.
3rd class levers reduce the output force, but increase output distance and speed

17. Which lever would have the highest mechanical advantage and why?
b has the largest input distance, giving the largest MA c b a

18. Pulley
Fixed pulley
1 support rope
IMA = 1

19. Pulleys
IMA = 2
Two supporting ropes

20. Pulleys
IMA = ? 2

21. Pulley
How many support ropes? 4
What is the IMA? 4

22. Wheel and Axle
Wheel connected to a shaft
GIVES YOU LEVERAGE

23. INCLINED PLANE FAMILY

24. Inclined planes
Ramps

25. Wedge
Two inclined planes stuck together

26. Screw
An inclined plane wrapped around a cylinder

27. What type of machine is this?
Compound: made of two or more machines
Two 1st class levers