1. What is the MA of a forklift that requires 480 N of input force and gives 6,600 N of output force? Round to nearest whole number
MA = OF/IF
MA = 6600 N
480 N
MA = 14
No Units for M.A.!

2. Efficiency

3. A. Factors of Efficiency
Output Work- Work done by a machine.
Input Work- Work done on a machine.

4. B. Efficiency Definition
Efficiency- comparison of output work to input work. Expressed as a percentage (%).

5. C. Efficiency Equation Efficiency = Output work x 100% Input work
E = OW x 100 % IW
Units of Measure:
Work = Joules (J)
Efficiency = percentage (%)

6. D. Practice Problems:
1. You cut the lawn with a hand mower. You do 250,000 J of work to move the mower. If the work done by the mower in cutting the lawn is 200,000 J, what is the efficiency of the lawn mower?
Efficiency = Output work x 100%
Input work
Efficiency = 200,000 J x 100%
250,000 J
Efficiency = 0.8 x 100%
Efficiency = 80%

7. 2. Suppose you left your lawn mower outdoors all winter. It’s now rusty. Of our 250,000 J of work, only 100,000 J go to cutting the lawn by the mower. What is the efficiency of the lawn mower now?
Efficiency = Output work x 100%
Input work
Efficiency = 100,000 J x 100%
250,000 J
Efficiency = 0.4 x 100%
Efficiency = 40%

9. gardening shears to become less efficient?
An old pair of garden shears requires 3,000 J of input work. The gardening shears give 2,200 J of output work. How efficient are the gardening shears?
What force caused the
gardening shears to become
less efficient?
E = OW X 100% IW
E = 2,200 J X 100%
3,000 J
E = X 100%
E = 73%
Friction- rust, parts becoming too tight/loose

10. E. Machines in Action
Efficiency is usually reduced because of friction. List the three types of friction:
Sliding friction
Rolling friction
Fluid friction
Friction causes some of the mechanical energy in a machine to be converted to thermal energy. Thermal energy is usually unwanted!

11. Activity With your Lab Partner
With your lab partner, examine the machine at your table. Try to carefully operate it. Observe and describe where friction might occur and list which type of friction is occurring in the space provided below.

12. Tool Name
Type of Friction
Location of Friction
Scissors
Sliding
Rolling
When blades close and open
On the pin that holds blades together
Stapler
When top and bottom pieces close
On the hinge between top and bottom
Hole Puncher
When handle pushed on bottom piece
When hinges/pins move handle
Ratchet
When metal parts grind past each other
When socket (bottom) rotates
Pliers
When metal parts grind or touch
On the pin that holds handles together
Can Opener
When metal cogs turn on each other
On the pin that hold the handles together

13. F. Why are Machines not 100% Efficient?
Actual mechanical advantage- the mechanical advantage a machine produces in a real situation. Efficiency is usually lost because of friction.
Ideal mechanical advantage- mechanical advantage in the absence of friction.