Work, Power, and Simple Machines

1. Work, Power, and Simple
Machines

2. Intro: Great Pyramid of Khufu in Egypt
• The Great Pyramid of Khufu stands over 137
meters high ( about 450 ft).
• Its base covers an area large enough to hold
10 football fields!!!
• More than 2 million stone blocks, each
weighing about 20,000 Newtons (about the
weight of two small SUV’s), make up the
structure!!!!

3. Intro: Great Pyramid of Khufu in Egypt
• It is one of the Seven Wonders of the World!!!
• Egyptians were credited with great effort and ingenuity for
this structure!!!
• Egyptians chiseled stone blocks from limestone quarries,
had to transport them to the pyramid site, and raise them
to the TOP!!!
• Egyptians only had SIMPLE MACHINES!!!
• Several thousand people worked for twenty years to build
the Great Pyramid!!
• With modern machinery, today it could be done in 1/5th of
the time with only a few hundred workers
• Lets make some machines!!!!!!....but first…lets get back to
basics!

4. I. What does work mean????
A. Work….what is it good for??
1. People use the work for many things…for example
when Levonas is sitting in his Life Guard chair…he
tells people he is at work.
a. Science disagrees with this statement!!
2. Work is done only when a force moves an object.
a. When you push, pull, lift, or throw an object you are doing
work.
3. Science definition: a force acting through a distance
is work.
a. Work is done whenever something is moved from one
place to another.
b. Your catapult did work!!!

5. I. What does work mean????
A. Work….what is good for
4. Another important requirement for work is that
the distance the object moves must be in the
same direction as the force applied to the object.
a. If you are holding a 45 lb plate in your arms, and you
walk forward have your arms done any work on the
weight?
b. The answer is NOOOOOO!!! The direction of the
movement of the bag is not the same as the direction
of the applied force!!!!

6. This would not be considered work!!

7. I. What does work mean????
A. Work….what is good for
5. Since the applied force is upward, whereas the
direction of movement is forward, the direction
of movement is NOT the same as the direction of
force by your arms.

8. I. What does work mean????
A. Work….what is good for
6. The amount of work done in moving an object is
equal to the force applied to the object times the
distance through which the force is exerted (the
distance the object moves).
a. Work = Force X Distance
b. Force = mass X acceleration (measured in kg/s2) but more
commonly measured in NEWTONS.
c. Distance is measured in meters
7. So work is measured in a NEWTON-meter….but we
call it a JOULE!!!!

9. I. What does work mean????
A. Work….what is good for???
8. If you lifted an object weighing 200 N through a
distance of 0.5m how much work would you do?
a. The force needed to lift the object must be equal to
the force pulling down on the object.
b. The force must be equal to what the objects weighs.
c. So the force is 200 N, the amount of work is equal to
200 N x 0.5 m, which is 100 J (Joules)

10. Example Problem: It takes work to
catch a flight!!
• A 600 newton woman who was waiting for the
flight lifted her 100 newton suitcase a distance of
0.5 meters above the airport floor and ran 25
meters.
• Calculate how much work was done by the
woman’s arms in moving the suitcase. Draw a
diagram showing the forces involved in this
situation.
• Explain how the work would change if she
dragged the suitcase along horizontally instead of
lifting it. Draw a diagram showing this situation.

11. ANSWERS TO EXAMPLE
1. The 600 newton woman does work when she is lifts
or drags the 100 newton suitcase, but NOT when she
carries it!
2. She lifts the suitcase 0.5 meters, so the work is equal
to the force needed to pick up the suitcase(100 N) X
the distance (0.5m), or a total of 50 J (Joules)
3. When she DRAGS the suitcase 25 meters the work
would be equal to 100 N X 25 meters, which is equal
to 2500 J.
a. Assuming that all force is exerted in the horizontal
direction!!!!

12. B. Power
1. Power is the rate at which work is done, or the
amount of work per unit of time.
a. Power is calculated by dividing the work done by the
time it takes to do it:
i. Power =
𝑊𝑜𝑟𝑘
𝑇𝑖𝑚𝑒
ii. Power =
𝐹𝑜𝑟𝑐𝑒 𝑋 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑇𝑖𝑚𝑒
b. The unit of power is simply the unit of work divided
by a unit of time, or the JOULE per second.
c. This unit is also called a WATT (W).
d. One watt is equal to 1 joule per second. (1 J/sec)

13. B. POWER
2. Watt and Electric appliances
a. A 50 watt light bulb does work at the rate of 50 joules per
second; in the same time a 110 watt light bulb does 110 joules
of work.
b. Kilowatt= 1000 watts
3. Explain why a bulldozer has more power than a person
with a shovel??
a. The bulldozer does more work in the same amount of time.
4. Why does it take more power to run up a flight of stairs
than it takes to walk up?
a. The same amount of work is done in both cases, but it takes
less time to run than to walk.
b. For the same amount of work, as TIME DECREASES, POWER
INCREASES.

14. B. POWER
1. What is power?
a. The rate at which work is done, or the amount of work
per unit of time.
2. What is relationship among power, work, and time?
a. Power equals work divided by time.
3. What is a watt?
a. One unit for power; 1 watt = 1 J/sec or 1 Newton-meter
/sec
4. A small motor does 4000 J of work in 20 sec. What is
the power of the motor in watts?
a. 200 watts

15. B. POWER
5. Suppose you ride in a sleigh being pulled by
horses at 16 kilometers per hour. Another sleigh
being pulled at 10 kilometers per hour travels
the same distance you do. Which horses are
more powerful? How is speed related to
power?
a. The horses pulling the faster sleigh are using more
power; because speed equals distance/time, power can
be expressed as force X speed. Therefore the greater the
speed, the greater the power if the force remains
constant!

16. C. Machines
1. An instrument that makes work easier is
called a machine; a device that helps you to
do something.
a. Machines are not always complicated like car
engines, computers etc.
b. Some machines are so simple they do not even
have moving parts.

17. C. Machines
4. How do Machines make work Easier???
a. WORK INPUT
i. Work that goes into the machine: WORK INPUT
ii. WORK INPUT comes from the FORCE that is applied to
the machine, or the EFFORT FORCE.
b. When you use a machine you supply the effort
force; because you exert this force over a
distance you put WORK into a machine!!

18. C. Machines
5. Work Output
a. Work done by a machine is called the work output.
b. The force the machine puts out is called the output
force.
c. The work output is used to overcome the force that
YOU AND THE MACHINE are working against.
d. The force that opposes the effort force is called the
resistance force.
i. The resistance force is often the weight of the object being
moved.

19. C. Machines
5. Work Output
e. Example of resistance force:
i. When using a shovel to move a rock your EFFORT is
opposed by the rock’s weight. The rock’s weight is the
resistance force.

20. C. Machines
6. Do Machines increase the amount of work??
a. Machines DO NOT increase the work you put into
them.
b. The work that comes out of the machine can
NEVER be greater than the work that goes into th
machine.
c. Like momentum, work is CONSERVED!!

21. D. Why do Machines Make Work Easier?
1. Machines make work easier because they
change either the SIZE or the DIRECTION of
the force put into a machine.
2. Three ways a machine can make work easier
a. It can multiply the size of the force but decrease
the distance over which the force moves.
b. It can multiply the distance over which the force
moves, but decrease the size of the force.
c. It can leave both force and distance unchanged,
but change the direction which the force moves.

22. D. Why do Machines Make Work Easier?
3. Most machines make work easier by
multiplying either force or distance BUT
NEVER BOTH!!!
4. No machine can multiply both force and
distance.

23. E. Determining How Helpful A Machine Is
1. Remember…work output (work that comes out of a
machine) can never be greater than work input
(amount of work put into a machine).
a. In reality the work output is always less than the work
input….do you know why????
i. Friction!!
2. Some of the work the machine does is used to
overcome the force of friction.
3. The comparison of work output to work input is called
the EFFICIENCY of the machine.
a. The closer the work output is to the work input the more
EFFICIENT the machine.
b. The more efficient a machine, the less friction is present.

24. F. Efficiency of a Machine
1. Efficiency is expressed as a percentage
a. Efficiency can never be greater than 100% bc
work output cannot be greater than work input.
b. There are no machines that are 100% efficient.
c. Machines with the smallest amount of friction
are the most efficient.
i. This is why we use oil/lubricants to keep a machine in
good condition.

25. F. Efficiency of a Machine
1. What do we mean by how helpful a machine
is??
a. How many times the machine multiplies the effort
force to overcome the resistance force.
2. The number of times a machine multiplies the
effort force is called the MECHANICAL
ADVANTAGE of the machine.
a. The mechanical advantage tells you how much force
is gained by using the machine.
b. The more times a machine multiplies the effort
force, the easier it is to do the job.
c. MECHANICAL ADVANTAGE= RF/EF
a. MA= Resistance Force/ Effort Force

26. TODAY’S ASSIGNMENT!!!
Use the internet to answer the following
1. List the six simple machines.
2. List three examples of each simple machine found in
every day use.
3. Explain how each simple machines work.
4. Explain the differences among three classes of levers.
5. Describe the difference between fixed and movable
pulleys.
6. Explain how the six simple machines are the basis for
all machines.
7. What is a compound machine??

27. G. Simple Machines
1. Inclined Plane
a. A ramp is an example of an inclined plane
b. A ramp decreases the amount of force you need
to exert, but it increases the distance over which
you must exert your force.
c. ***What you gain in force you pay for in
distance!!
d. Ramp would not alter the amount of work
needed, just the way in which the work is done.

28. G. Simple Machines
1. Inclined Plane
e. Inclined plane is a flat slanted surface with NO
moving parts.
f. The less slanted the inclined plane, the longer
the distance over which the effort force is
exerted and the more the effort is multiplied.
g. The mechanical advantage of an inclined plane
increases as the slant decreases.

29. G. Simple Machines
2. Wedge
a. A wedge is an inclined plane that MOVES.
b. Instead of an object moving along the inclined
plane, the inclined plane itself moves to raise the
object.
c. As a wedge moves a greater distance it raises the
object with greater force.
d. The longer and thinner a wedge is, the less the
effort force is required to overcome the
resistance force.

30. G. Simple Machines
2. Wedge
e. When you sharpen a wedge, you are increasing
the mechanical advantage by decreasing the
effort force that must be applied in using it.
f. A knife and ax are two examples.
g. Go online and find how a lock depends on the
principals of the wedge.
h. The zipper is another important application of
the wedge.

31. G. Simple Machines
2. Wedge
i. Zippers join or separate two rows of interlocking
teeth.
j. The part of the zipper that you pull up or down
contains three small wedges.
k. Have you ever tried to close a zipper with your
hands??? It is almost impossible to create
enough force.
l. Without these wedges you would not be able to
close the zipper; it changes a weak effort force
into a strong one.

32. G. Simple Machines
3. Screw
a. A screw is an inclined plane wrapped around a
central bar or cylinder to form a spiral.
b. A screw multiplies the effort force by acting through
a long distance.
c. The closer together the threads, or ridges, of a screw,
the longer the distance over which the effort force is
exerted and the more the force is multiplied.
d. The mechanical advantage of a screw increases when
the threads are closer together.
e. Screws increase the amount of force applied to
them, but decrease the distance over which the
force is applied.

33. G. Simple Machines
4. Lever
a. A lever is a rigid bar that is free to pivot, or move
about, a FIXED POINT.
b. The fixed point is called the FULCRUM.
c. If you were ever on a see saw, or used a screw
driver to pry something open you have used a
lever.
d. When a force is applied on a part of the bar by
pushing or pulling it, the lever swings about a
fulcrum and overcomes resistance force.

34. G. Simple Machines
4. Lever
e. If you are using a crow bar to pry a nail out of a
board.
f. When you push down on the end of the crowbar,
the nail moves in the opposite direction.
g. The crowbar changes the direction of the force.
h. But the force exerted on the nail by the crowbar
moves a shorter distance than the effort force
you exert on the crowbar.

35. G. Simple Machines
4. Lever
i. You push down through a longer distance than
the nail moves up. Because WORK IS
CONSERVED, this must mean that the crowbar
multiplies the effort force you apply.

36. G. Simple Machines
5. Classifying Levers
1. The relative positions of the effort force,
resistance force, and fulcrum determine the
three classes of levers.
2. Levers such as a crowbar, seesaw, and pliers are
first class levers.

37. G. Simple Machines
5. Classifying Levers
a. The relative positions
of the effort force,
resistance force, and
fulcrum determine the
three classes of levers.
b. Levers such as a
crowbar, seesaw, and
pliers are first class
levers.

38. G. Simple Machines (FIRST CLASS LEVERS)
First Class Levers
a. Fulcrum in the center - between load & effort
b. The lever changes the direction of force
c. The fulcrum is placed close to the load , and this will
let you move the load with just a small applied force
(effort)
d. This type of lever system gives you a mechanical
advantage , which means that the force you apply
gets multiplied , so you can put a large force on the
load.

39. G. Simple Machines (FIRST CLASS LEVERS)
3. First Class Levers
e. The trade-off of using a lever like this is that you have
to apply a force over a large distance , and the load
itself will move only a short distance
• Examples of 1 st Class Levers:
• See-saw
• Scissors
• Pliers

40. G. Simple Machines (FIRST CLASS LEVERS)
Second Class Levers
a. The load is in the center - between the fulcrum and
the applied force or effort
b. Causes the load to move in the same direction as the
force you apply
c. When the load is nearer to the fulcrum, the effort
needed to lift the load will be less.
d. If you want to move a very large load with a small
effort, you must put the load very close to the
fulcrum

41. G. Simple Machines (FIRST CLASS LEVERS)
Second Class Levers • Examples of 2nd Class
Levers:
• Wheelbarrow
• Nutcracker

42. G. Simple Machines (FIRST CLASS LEVERS)
Third Class Levers
a. The applied force or effort is in the center - between the
load and fulcrum
b. This lever system does not give any mechanical advantage
c. No matter where you apply the force, the force you apply
must always be greater than the force of a load
d. No matter how close or how far the load is from the
fulcrum, the effort used to lift the load, has to be greater
than the load!
e. The load moves in the same direction as the force you
apply
f. A motor is usually used with this lever system to lift loads
at a distance
g. Speeds up movement

43. G. Simple Machines (FIRST CLASS LEVERS)
Third Class Levers • Examples of Third Class
Levers:
• Your bent arm
• Fishing rod

44. G. Simple Machines
6. Pulleys
a. Pulley is a rope, belt, or chain wrapped around a
grooved wheel.
b. A pulley can function in two ways:
i. Change the direction of the force
ii. Change the amount of force

45. G. Simple Machines
7. Fixed Pulleys
a. May be single or combination
b. Doesn't change position
c. Makes work easier by changing the direction
of the applied force
d. The force required to lift the load remains
the same as lifting it without the pulley

46. G. Simple Machines (Fixed Pulley)
e. But it is much easier it is to raise a flag from
the ground, instead of climbing up the pole
f. If a force needs to be applied around a
corner, a pulley allows us to overcome
friction
g. The only pulley that when used individually,
uses more effort than the load to lift the load
from the ground
h. The fixed pulley is attached to an unmovable
object like a ceiling or wall

47. G. Simple Machines (Fixed Pulley)
i. Acts like a first class lever with the fulcrum
being located at the axis
j. The bar or lever arm becomes a rope
k. The advantage of the fixed pulley is that you
do not have to pull or push the pulley up and
down.
l. The trade-off is that you have to apply more
effort than the load

48. Fixed Pulley

49. G. Simple Machines
8. Movable Pulleys
a. May be single or combination
b. A pulley that moves with the load ( both the
load and the pulley move)
c. The load moves in the same direction as the
applied force
d. The movable pulley allows the effort to be
less than the weight of the load

50. G. Simple Machines (Movable Pulleys)
e. It takes less force to raise an object than if
you used only your hands
f. The amount of force required depends on
the number of supporting ropes
g. The greater the number of pulleys and
supporting ropes, the smaller the force
required.

51. G. Simple Machines (Movable Pulleys)
h. Trade-off : the less force required, the
greater the distance the rope must be pulled
further than the load actually moves
i. The movable pulley acts as a second class lever
ii. The load is between the fulcrum and the effort
force
iii. The main advantage of a movable pulley is that
you use less effort to pull the load

52. Movable Pulley

53. G. Simple Machines
9. Single Pulley
a. A single pulley reverses the direction of a
force
b. With one pulley, the force you must pull with
is the same as the weight of the object .
c. In order to raise the object a height of 1
meter, you must pull the rope 1 meter
d. Trade-off : the end of the rope must move a
greater distance than the load

54. G. Simple Machines
10. Combination Pulley
a. Two or more pulleys connected together
b. Allow a heavy load to be lifted with less force
c. Effort needed to lift the load is less than half
the weight of the load
d. The main advantage of this pulley is that the
amount of effort is less than half of the load
e. Trade-off - you need more rope and you
need to pull more rope

55. G. Simple Machines (Movable Pulleys)
11.Wheel and Axle
a. A wheel with a rod, called an axle, through its
center lifts or moves loads
b. The axle is a rod that goes through the wheel
c. This lets the wheel turn
d. The wheel & axle can be used as a tool to
multiply the force you apply OR to multiply the
distance traveled
e. A lever that is able to rotate through a complete
circle (360° )

56. G. Simple Machines (Movable Pulleys)
11. Wheel and Axle
f. The circle turned by the wheel is much larger
than the circle turned by the axle.
g. The increased distance over which the force is
applied as the wheel turns results in a more
powerful force on the axle, which moves a
shorter distance
h. Trade-off-: The larger the diameter of the wheel,
the less effort you need to turn it, but you have
to move the wheel a greater distance to get the
same work done.