Class instruction on work and machines

2. 3 BIG Concepts:
 Calculating and understanding work
 Calculating and understanding MA
 Force-distance trade-off

3. Before
reading Statement After
reading
Text evidence for or against
(include the page # and paragraph #
along with your citation)
Write an “A” if you agree or “D” if you disagree for each statement.
A force acting on an object does work
even if the object doesn’t move.
A mover who pushes a piece of furniture up a ramp
and into a truck does the same work as a mover who
simply lifts the piece of furniture directly onto the
truck.
You are using more power if you do the
same amount of work in a shorter time.
Machines put out more work than
we put in.
Machines can increase the size of
a force that is applied to a load
The work you do on a machine (work
input) is the same as the work the
machine does on a load (work output)

4. Brainstorming:
What does it mean to “WORK”?

5. 1. Analyze the picture and
formulate your own scientific
definition of WORK.
2. Compare and contrast your
definition of work to the
definition on p. 129 of your
Interactive Textbook. How are
they similar and different?
3. SHOW AND TELL: Work with a
classmate to prepare a short
demonstration of WORK and
NOT WORK.
• Define WORK
• 1 example of WORK w/
explanation
• 1 non-example of WORK
w/ explanation

6. 2N X 3m = 6N•m or 6 Joules (J)
600N X 0m = 0N•m or 0 Joules (J)

7. Which of the following actions do more work on an
object?
• Lifting an 80 N box 1 m up off the floor
• Lifting a 160 N box 1 m up off the floor
• Lifting a 90 N box 2 m up off the floor
• Lifting a 100 N box 1.5 m up off the floor

8. – In which situation is a person doing work on an
object?
a) A school crossing guard raises a stop sign that
weighs 10N.
b) A student walks 1m/s while wearing a
backpack weighing 15N.
c) A man exerts 500N of force on a rope
attached to a house but the house doesn’t
move.
d) A worker holds a box 1m off the floor.

9. Which example does NOT involve work being
done?
a) A waiter carrying a food tray across a
dining room.
b) A person places a heavy box up on a high
shelf.
c) A rocket accelerates into space.
d) A truck pulling a trailer

10. • You lift a chair that weighs 50N to a height of 2m and
carry it 10m across the room. How much work do
you do on the chair?

11. • You apply a 200N force to move a 500N boulder 5m
to the edge of a cliff. The boulder falls 100m. How
much work did you do to the boulder?

12. • You apply a 200N force to move a 500N boulder 5m
to the edge of a cliff. The boulder falls 100m. How
much work did gravity do to the boulder?

13. • A rope is thrown over a beam and one end is tied to a
300N bundle of lumber. You pull the free end of the
rope 2m with a force of 400N to lift the lumber off
the ground. How much work have you done?

14. – EQ: How do machines make work easier?
– EA: Machines make work easier by changing the size
(magnitude) and/or direction of a force.

15. – EQ: Can machines put out more work than we put in?
STUDENT 1 STUDENT 2
• Read and summarize
I.T. p. 132
• Read and summarize
I.T. pgs 137-138 (top
half)
BOTH STUDENTS:
• Discuss your readings and record 3 key ideas from
the text.

16. – Mechanical Advantage (MA)
• Some machines can make work easier by
increasing output force applied to an object.
• Mechanical advantage is the number of times a
machine multiplies the input force.
Mechanical Advantage (MA) =
Output force (N)
Input force (N)

17. Load
Fulcrum
Effort side
Resistance side
Experiment
1. Place the fulcrum in the middle (50cm) and the load (100g) at one
end. Observe how much force is needed to lift the load.
2. Move the fulcrum closer to the load and observe how much force
is needed to lift the load.
3. Move the fulcrum farther from the load and observe how much
force is needed to lift the load.
4. Try to balance different masses at each end by adjusting the
position of the fulcrum.

18. Analysis
1. Where should you move the fulcrum to make the load easier to
lift?
2. The ____________ (closer/farther) the fulcrum is to the load,
the ____________ (more/less) force needed to lift the load.
3. The greater the length of the effort side, the __________
(greater/less) force needed to lift the load.
4. The greater the length of the resistance side, the __________
(greater/less) force needed to lift the load.
Load
Fulcrum
Effort side
Resistance side

19. Sample Test Question
A lever has a mechanical advantage of 2. The input force is
100N. What is the output force?
Load
Fulcrum
Effort side
Resistance side

20. – Mechanical Advantage
• Suppose that you exert 60N on a machine and the
machine exerts 240N on another object. What is
the machine’s mechanical advantage?
Mechanical Advantage (MA) =
Output force (N)
Input force (N)

21. – Mechanical Advantage
• A mechanic uses a pulley to lift an engine out of a
car. She applies a force of 200N to one end of the
rope and the rope applies a force of 600N to the
engine. What is the mechanical advantage of the
pulley?
Mechanical Advantage (MA) =
Output force (N)
Input force (N)

22. – Mechanical Advantage
• A worker uses a lever to lift a load. She applies a
force of 100N and the lever applies a force of 25N
to lift the load. What is the mechanical
advantage of the lever?
• What might this lever look like?
Mechanical Advantage (MA) =
Output force (N)
Input force (N)