1. Work & Mechanical Advantage
Introductory Video

2. The Meaning of Work
You do work on an object when you exert a force on the object that causes the object to move some distance.
Pushing a child on a swing
Pulling your books out of your book bag
Lifting a bag of groceries out of a shopping cart
The object must move some distance as a result of your force!
No movement = No work!
The force you exert must be in the same direction as the object’s motion.

3. Yes No Work or Not Work? Example Direction of Force
Direction of Motion
Doing Work?
Yes No

4. Yes No Work or Not Work? Example Direction of Force
Direction of Motion
Doing Work?
Yes No

5. Calculating Work
The amount of work you do depends on both the amount of force you exert and the distance the object moves.
Work (J) = Force (N) X Distance (m)
Joule = 1 N•m
The amount of work you do when you exert a force of 1 N to move an object a distance of 1 m.
Work = Force X Distance

6. Calculating Work If you exert a force of 20 N to push a desk
10 m, how much work did you do?
Formula:
Work:
Answer:
W = F X D
W = 20 X 10
W = 200 J

7. What is a Machine? A device that makes work easier or more efficient.
Changes the size of the force.
Changes the direction of the force.
2 types of work are done using machines:
Work Input
Work Output

8. Work Input/Work Output
Work Input – the work you do on the machine.
You apply a force and move it through a certain distance.
Work Output – The work done by the machine.
Machines apply the force through a distance.
Opposes the force you and the machine are working against.
A screwdriver lifting up on the lid of a can.
Output
Force
Input
Force

9. Work Input/Work Output
Force and distance don’t need to be equal, only the products do!
If I wanted to raise this rock off the ground, the lever will need to expert 60N of force to lift it 2 meters into the air. How much output work is required to do this?
Formula:
Work:
Answer:
W = F X d
60 X 2
120 J

10. Work Input/Work Output
If my input work is equal to my output work, how much force will I need to put into the lever to push it 6 meters down?
Formula:
Work:
Answer:
F = W/d
120/6
20 N
The lever and I do the same amount of work but I traded a
greater distance on my end for a greater force on the other end.

11. Mechanical Advantage
Mechanical Advantage – how many times a machine multiplies a force.
Compares input force with output force.
Work output is always less than work input because of friction.
Mechanical Efficiency – compares the machine’s work output to the work input but also takes into consideration friction.
MA = output force/input force
ME = work output/work input X 100

12. Calculating MA
Tom’s pulley has an output force of 60N and an input force of 15N, what is the Mechanical Adavantage of Tom’s pulley?
Formula:
Work:
Answer:
MA = output force/input force
MA = 60/15
MA = 4N

13. Calculating MA and ME
Tom’s pulley has an output work of 6J with 12J of work being put into it. What is the Mechanical Efficiency of Tom’s pulley?
Formula:
Work:
Answer:
ME = work output/work input X 100
ME = 6/12 X 100
ME = 50%