1. Mechanical Advantage & Effeciency

2. Objectives Explain how a machine makes work easier
Describe and give examples of the force-distance trade-off that occurs when a machine is used
Describe & Calculate mechanical advantage
Describe & Calculate effeciency
Explain why machines are not 100% efficient

3. What is a machine? Machines make work easier by
Changing the amount of ___________ you exert
Changing the __________ over which you exert the force
Changing the __________ the force is exerted

4. Which is easier? Opening a paint can with your fingers?
Opening a paint can with a screwdriver? OR

5. Which is easier? Pushing a heavy box up a ramp into a truck?
Lifting a heavy box into a truck? OR

6. When using a machine to do work, two forces are involved.
_________ Force (Fin)
The force ____ apply to the machine in doing work (Win)
__________ Force (Fout)
The force that the _________ applies in doing work (Wout)

7. Two types of work are involved.
Work input is the amount of work done _____ a machine.
Input force x input distance
Work output is the amount of work done _____ a machine.
Output force x output distance
How are the two related?

8. Force-distance trade-off
To ________ the force needed, increase the ____________
To _______ the force needed, decrease the ____________
Examples: wheelbarrow and hammer

9. Force-Distance Trade-off (increases force)
Wheel barrow
________ in a greater distance (lift handle of wheelbarrow)
_________ applied a shorter distance (load in wheelbarrow lifted)

10. Force-Distance Trade-off (decreases force)
Hammer
_____________ applied over a short distance
_____________ applied over a long distance

11. Measuring the benefits: Mechanical Advantage
Mechanical Advantage tells you how many times the machine ____________ the force.
a machine with a large mechanical advantage can make lifting a heavy load easier
Actual Mechanical Advantage
Ideal Mechanical Advantage

12. Calculating Mechanical Advantage
What is the mechanical advantage of a machine that applies 200N to an object when you apply 50N to the machine?
Equation

13. Calculating Mechanical Advantage
You apply 2000 N to a machine and the machine applies 200 N to an object. What is the mechanical advantage?
Equation
MA = (Fout)/(Fin)
MA = (200N)/(2000N)
MA = 0.1

14. Calculating Mechanical Advantage
You apply 10 N to a machine and the machine applies 10 N to another object. What is the mechanical advantage.
Equation

15. Mechanical Advantage:What does it mean?

16. However, some output work is lost due to ___________.
Efficiency
We said that the input work _________ the output work, or:
Win = Wout
However, some output work is lost due to ___________.
The comparison of work input to work output is called ___________________.
No machine has ______ percent efficiency due to friction.
What would improve the efficiency of a machine? (Hint: What reduces friction?)

17. Calculating Efficiency
How efficient is a machine that takes 40 J of work and produces 30 J of work?
Equation

18. Calculating Efficiency
You do 250,000 J of work to cut a lawn with a hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower?
Equation