1. Using Machines
Chapter 3, Lesson 2

2. What is a machine?
A machine is any device that makes doing something easier.
Some machines are simple and other machines are more complex.
Gabe Palmer/Alamy

3. Input and Output Forces
Input force is the force you apply.
Output force is the force the machine applies.
The machine changes the input force to an output force.

4. Input and Output Work
Input work (W in) is the work you do to move the machine.
Output work (W out) is the work the machine does on the object you are trying to move.

5. IMPORTANT
Machines never decrease the amount of work required to do a task. They make the work easier.

6. 3 Ways Machines Make Work Easier:
They can change the size of the force needed.
They can change the distance the force acts.
They can change the direction of the force.

7. Changing the Size of the Force
A crowbar changes a small input force to a larger output force.

8. Changing the Distance
A rake increases the distance the force acts. It changes a small input distance to a large output distance.

9. Changing the Direction of a Force
A pulley changes a downward input force to an upward output force used to lift an object.

10. How does the hammer help?

11. Mechanical Advantage
Most machines help us by changing the size of the force. MA tells us how much the machine multiplies our input force.
MA = F out / F in
mechanical = output force / input force
advantage
(no units) (Newtons) (Newtons)

12. What does MA mean?
If MA is > 1, the machine is helping us by changing our force. (crowbar)
If MA is = 1, the machine is keeping our input and output force the same. (fixed pulley)
If MA < 1, the machine is not helping us by changing our force. (rake)

13. A carpenter uses a crowbar to pry up a board
A carpenter uses a crowbar to pry up a board. He applies 525 N to the end of a crowbar. The force exerted on the board is 1575 N. What is the mechanical advantage of the crowbar?

14. While raking leaves, a woman applies a 32 N force to a rake
While raking leaves, a woman applies a 32 N force to a rake. The rake has an output force of 16 N. What is the mechanical advantage of the rake?

15. The same machine is used to move several different objects of various weights. In order for the machine to lift the object, it needs to apply an output force that is equal to the weight of the object. Calculate the MA of the machine using data from the table. Use the MA to help you figure out the input force applied to the machine to lift object B and C and the output force produced by the machine to lift object D.
Object
Output Force
Input Force A
15 Newtons
3 Newtons B
30 Newtons C
39 Newtons D
60 Newtons

16. Charlie uses a lever to lift an object. He applies a force of 11 N
Charlie uses a lever to lift an object. He applies a force of 11 N. Using the lever, he is able to lift an object that weighs 132 N. What is the MA of the lever? Is this lever helpful?

17. Interpreting Data Example
Number of students helping to pick up litter
Number of hours needed to clean up the park
Number of garbage bags filled in 1 hour
10 students
8 hours
8 bags
20 students
5 hours
16 bags
30 students
3.5 hours
24 bags

18. Efficiency Efficiency = Wout / Win x 100
Remember machines never reduce the amount of work.
In fact, machines actually give us more work to do. Wout < Win because of friction.
Efficiency tells us how much of the Win is changed to useful Wout by the machine.
Efficiency = Wout / Win x 100
(%) (Joules) (Joules)

19. How can you increase efficiency of a machine?
Add grease or oil to the parts to reduce friction.
A machine will never be 100% efficient.

20. A mechanic does 78.0 J of work pulling the rope on a pulley to lift a motor. The output work of the pulley is 64.0 J. How efficient is the pulley?

21. Bonus: Use the information to figure out the Efficiency and the MA of the Ramp.
You use a force of 300 Newtons to push a box up a ramp. The box weighs 500 Newtons.
2.2 meters
1.2 meters

22. Bonus: Use the information to figure out the Efficiency and the MA of the Ramp.
You use a force of 420 Newtons to push a box up a ramp. The box weighs 500 Newtons.
1.5 meters
1.2 meters