Work, power, and machines notes from class.

1. AKS 15b – analyze the relationship between work, power, and time
AKS 15c – explain how machines make work easier

2. Brainstorming:
What does it mean to “WORK”?
Anticipation Guide:
After completing the Before Reading portion,
work with your group to write one question
that would help you determine whether a
statement (or statements) is true or false.

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.
Can it be proven
mathematically? HOW?
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. Questions (1st Period):
1. Is force the same as work?
2. How can we calculate work?
3. What is a load?
4. If you push something and it doesn’t move, is it
still work?
5. How much work can machines put out?
6. What is work?
7. Does direction affect the force applied?
8. What is the difference between work input and
work output?

5. Questions (2nd Period):
1. What is the difference between power and work?
2. How much force is being applied to an object?
3. What is the sci. definition of work?
4. Can machines increase the size of force applied to a
load?
5. Is the work you do on a machine the same as the work
the machine does on a load?
6. Does the quality of the machine affect the amount done
by the machine?
7. What is the difference between force and work?
8. How can you calculate the work done by simple
machines?

6. Questions (3rd Period):
1. What is the difference between work input and work
output?
2. What effect do machines have on work and power?
3. How does angle/direction affect the work done on an
object?
4. Do machines apply the same amount of force and
distance as a human?
5. What is work?
6. Does an object need to move for work to be done?
7. What is a machine?
8. Can machines increase the magnitude of a force applied
to a load?

7. Questions (4th Period):
1. What is work?
2. How do machines make work easier?
3. In a shorter amount of time, if you use more power are
you putting more work?
4. Does the amount of time you spend doing work affect
the amount of work you do?
5. What are the differences between work input and work
output?
6. Can machines increase the magnitude of a force applied
to a load?
7. EPIC FAIL!
8. Do machines or people do more work?

8. 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

9. 2N X 3m = 6N•m or 6 Joules (J)
600N X 0m = 0N•m or 0 Joules (J)

10. 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

11. – 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.

12. 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

13. • 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?

14. • 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?

15. • 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?

16. • 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?

17. A cart is pushed 10 m down the hall with a force of
100N in 5s.
• How much work is done?
• How much power is used?

18. Record the fastest times in the chart below:
Name Time (s) Analysis
Copy and complete the following questions:
1. What was the work done in this
demonstration?
2. Who did the most work? How do you
know?
3. Which student was the most powerful?
How do you know?
4. What factors (variables) may have
affected your results?

19. – What is the advantage of using a power tool over
a hand tool to do the same amount of work?
a) It uses less force.
b) It uses less energy.
c) It requires less time.
d) It requires more time.
– REMEMBER: More power means you can work
faster!
19

20. 20
Record the appropriate information in the spaces below:
Student Name
Force
Distance
Time
Work
Power
Analysis
1. What was the work done in this
experiment?
2. Who did the most work?
3. Which student was the most
powerful? How do you know?
4. What factors (variables) may
have affected your results?
2.2 kg = _____ N
1.1 kg = _____ N Power =
Work (J)
time (s)

21. Mr. Cox and Mrs. Steele each lift an identical stack
of books the same distance onto a table, but Mr. Cox
does the job twice as fast. Therefore his actions
involve twice as much
a) Work input
b) Work output
c) Power
d) Efficiency

22. Work = force and motion in the same direction.
Units = Joules (J)
Power = the rate at which work is done.
Units =Watts (W)

23. Work = ____ and ______ in the same ________.
Units = ________
Power = the _____ at which ______ is done.
Units = ________

24. – Mechanical Advantage and Efficiency
• What does it mean to have an ADVANTAGE?
• What does EFFICIENT mean?

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

26. – 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)

27. – 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)

28. – 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.
What is the mechanical advantage of the lever?
Mechanical Advantage (MA) =
Output force (N)
Input force (N)

29. – Mechanical Efficiency
• Some of the work done by a machine is always
used to overcome the friction created by the
machine.
• Mechanical efficiency tells you what percentage of
the work input gets converted into work output.
Mechanical Efficiency (ME) =
Work output (J)
X 100
Work input (J)

30. – Mechanical Efficiency
• What is the mechanical efficiency of a machine
whose work input is 1200J and work output is
900J?
Mechanical Efficiency (ME) =
Work output (J)
X 100
Work input (J)

31. – Mechanical Efficiency
• You do 500J of work to a rope attached to a pulley.
The pulley does 400J of work to lift a load. What
it is ME of the pulley?
Mechanical Efficiency (ME) =
Work output (J)
X 100
Work input (J)

32. –MA and ME
• You are measuring force and distance for a lab
activity. Your measurements indicate that you
apply 100N to move a lever 2m. The lever
applies 300N to move a load 1m.
1. What is the MA of the lever?
2. What is the ME of the lever?
3. How much work was used to overcome the
friction of the machine?

33. – Define machine, input force, and output force (p. 216-217)
Copy and complete the following chart with a picture, a
description (definition), and a real-world example (p. 222):
Lever Pulley
Wheel and Axle Inclined Plane
Wedge Screw

34. – Levers
• Levers

35. – Pulleys

36. – Wheel and Axle

37. – Inclined Plane

38. • Wedges

39. – Screw

40. 1. Mr. Cox wants to remove the lid from a paint
can. What simple machine should he use as a
tool?
2. What type of simple machine is used to split
things apart?
3. Both the wedge and the lever are used in the
operation of which tool?
a) Shovel
b) steering wheel
c) Wheelbarrow
d) block and tackle (p. 224)

41. 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.

42. 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

43. 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

44. Two children are playing on a seesaw in the park.
Sarah, who weighs less than Jeff, is suspended in the
air. Where could you move the fulcrum in order to
raise Jeff into the air?

45. – Which of the following items is most similar to the
lever in the diagram? (p. 223)
a) Seesaw
b) Wheelbarrow
c) Bottle opener
d) Arm lifting a weight

46. – What simple machines are found on a pair of scissors?
– What do you call a machine made up of 2 or more
simple machines?
Lever
Wedge
Fulcrum

47. – What simple machines are used to make a
wheelbarrow?

48. – What simple machines are found on this
compound machine?