Work and Machines
Table of Contents
What Is Work?
How Machines Do Work
Simple Machines
Work and Machines
Learning Objectives
1. Identify when work is done on an object.
• Force, Movement in the same direction as the force
2. Calculate the work done on an object.
3. Define and calculate power.
Work and Machines - What Is Work?
The Meaning of Work
Work is done on an object when the object moves in the same
direction in which the force is exerted. Work = Force x distance
Work and Machines - What Is Work?
Calculating Work
A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It
moves the car a distance of 5 m. What is the work done by the tow
truck?
Work = Force x distance (in the direction of the force)
Work = 11,000 N x 5.0 m = 55,000 N x m (Newton meters)
1 N x m = 1 Joule = 1 J
So, Work of the tow truck = 55,000 Joules or 55,000 J
Work and Machines - What Is Work?
Calculating Work
Suppose you get super strong exert a force of 500 N by moving a
person 2 m out of the way of a moving truck. How much work did you
do?
Work = 500 N x 2 m = 1000 N x m (Newton-meters)
So, Work = 1000 Joules or 1000 J
Work and Machines
Electricity Usage and Power
The amount of money you add to the electric bill can
be determined by how long you use certain appliances
and the power rating of those appliances.
Power is the rate at which the work gets done, so
power is the amount of work done in a certain amount
of time.
Power = Work/Time or
(Force x Distance)/Time
And Power = strength of the electric current x voltage
Power is measured in Watts (W) or kilowatts (kW).
Examples- Light Bulbs range from 40 W to 100 W.
1 Watt = 1 (N x m)/s or 1 J/s
1000 Watts = 1 kilowatt
Work and Machines - What Is Work?
Calculating Power
A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It
moves the car a distance of 5 m in 25 seconds. What is the power of
the tow truck?
What quantity are you trying to calculate?
The Power (P) the tow truck uses to pull the car = __
What formula contains the given quantities and the unknown quantity?
Power = Work/Time = (Force X Distance)/Time
Perform the calculation.
Power = (11,000 N X 5.0 m)/25 s
Power = (55,000 N•m)/25 s or 55,000 J/25 s
Power = 2,200 J/s = 2,200 W
1 Joule per second = 1 Watt
1000 Watts = 1 kilowatt or 1000 W = 1 kW
Work and Machines - What Is Work?
Calculating Power
A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It
moves the car a distance of 5 m in 25 seconds. What is the power of
the tow truck?
Look Back and Check
Does your answer make sense?
The answer tells you that the tow truck used 2,200 W to pull the car.
This value is about the same power that three horses would exert, so
the answer is reasonable.
Work and Machines - What Is Work?
Calculating Power
Practice Problem
A motor exerts a force of 12,000 N to lift an elevator 8.0
m in 6.0 seconds. What is the power produced by the
motor?
(12,000 N x 8.0 m)/6.0 s
= 16,000 W or 16 kW
Work and Machines
Electricity Usage and Power
Electric companies charge about 7 cents
($0.07) per kilowatt-hour (kWh).
So, if use an appliance with a 1000 W (or 1 kW)
power rating for 100 hours over the course of a
month, then you used 1 kW x 100 hours
= 100 kWh.
To determine the money added to the bill,
multiply the kWh by the money per kWh…
100 kWh x 0.07 dollars/kWh = $7.00
Work and Machines - What Is Work?
Calculating kilowatt-hours & Cost
Suppose you use your DVD player & TV with a
combined power rating of 250 W for 40 hours over the
course of a month. How many kilowatt-hours did you
add to the electric bill? Remember to convert units.
How much money did you add to the electric bill if the
electric company charges 7 cents ($0.07) per kWh?
250 W = 0.250 kW
Amount of kWh = 0.250 kW x 40 hours = 10 kWh
Cost = 10 kWh x $0.07 per kWh = $0.70 or 70 cents
Work and Machines
Noggin Knocker Calculations
Work and Machines
Which of the following is NOT an example of doing
work?
A.
B.
C.
D.
E.
Pushing a cart around in the grocery store.
Lifting your books.
Holding a person straight above your head.
Pulling a person out of quicksand.
Me in 10 years.
Work and Machines
If a 100 N force to the right is used to move a couch
5 m to the right, then how much work was done?
A.
B.
C.
D.
500 N x m or 500 Joules
20 N x m or 20 Joules
500 N
No work was done.
Work and Machines
The rate at which work gets done is
A.
B.
C.
D.
Very slow if I’m in charge.
Force.
Work.
Power.
Work and Machines
To calculate power, you divide work (or force x
distance) by
A.
B.
C.
D.
Power.
Time.
Force.
Distance.
Work and Machines
Which of the following are units for power?
A.
B.
C.
D.
Newton x meters (N x m)
Newtons
Joules (J) or Joules x seconds (J x s)
Watts (W) or kilowatts (kW)
Work and Machines
2000 W = ___________ kW
A.
B.
C.
D.
2 kW
20 kW
200 kW
2 cans of A & W
Work and Machines
How much power is required of you if you use 50 N
to lift your books 1 m in 2 seconds?
A.
B.
C.
D.
100 W
50 W
25 W
0W
Work and Machines
Your electric bill is determined by multiplying a cost
of about 7 cents ($0.07) for every
A.
B.
C.
D.
Watt-seconds.
Kilowatt-hour.
Kilowatt-seconds.
Watt-minutes.
Work and Machines
Suppose you play Call of Duty: Black Ops for 700
hours over the course of a month. The combined
power rating of the TV and the X-Box is 500 Watts.
What is the number of kWh for your gaming?
Remember to convert units if needed.
A.
B.
C.
D.
350,000 kWh
1200 kWh
350 kWh
0.350 kWh
Work and Machines
So if you had to pay 7 cents ($0.07) per kWh and
your gaming racked up 350 kWh, then how much
money did you add to the electric bill due to your
gaming addiction?
A.
B.
C.
D.
$24.50
$2.45
$2450
$50.00
Work and Machines
Noggin Knocker Calculations
Work and Machines
Homework- p. 113: 1a, 1b, 1c, 2b, 2c, 3b, & 4
1a- Work is when you apply a force on an object and this causes the
object to move a certain distance.
1b- The object has to move in the same direction in which the force is
applied.
1c- Work is done for rolling a bowling ball and kicking a football.
2b- Work = Force x Distance (in same direction as the force)
2c- Same amount of work b/c 2 N x 3 m = 6 J and so does 3 N x 2 m
3b- Power is Work divided by the time it takes to get the work done.
4- P = (Force x Distance)/Time = (22 N x 3.0 m)/6.0 s = 11 Watts
Work and Machines
Experiment Problem from the Forces Test
Suzie and Markie are attempting to discover how to make moving
large objects easier. They both believe that lighter objects are
easier to move across a surface. They design an experiment to
test out their prediction using a small wooden cart, a force sensor,
and weights.
Hypothesis- Lighter objects are easier to move across a surface.
Ind. Variable- weight or mass
Dep. Variable- frictional force or force required to move the object
or distance moved in a certain amount of time
Constants- same surface, same incline, same distance moved,
same force sensor, same amount of pull/time for each
measurement
Work and Machines
Experiment Problems
Determine the hypothesis, independent variable, dependent
variable, and 2 or more constants for the experiment:
A student believes that bacteria grows quicker in warmer
environments and slower in a cooler environment. This student is
using petri dishes (little plastic dishes) and incubators of varying
temperatures to cultivate the bacteria.
Hypothesis- Bacteria will grow quicker the warmer it gets (as
temperature goes up).
Ind. Variable- Temperature
Dep. Variable- Amount of bacteria grown
Constants- Same size petri dishes, same amount of bacteria in
each dish to start with, same amount of light, etc.
Work and Machines
Plant Experiment
Determine the independent variable(s), dependent variable, 2 or more
constants, and the control group:
Flowers in a greenhouse are fertilized with a mixture of nitrogen (N), phosphorus
(P), and potassium (K). A student has used different amounts of these parts of
fertilizer to determine which component is most responsible for good growth.
Examine the table.
Plant A
Plant B
Plant C
Plant D
N = 90
N=5
N=0
N=5
P=5
P = 90
P=0
P=5
K=5
K=5
K=0
K = 90
Ind. Variables- Amount of different fertilizers (N, P, & K)
Dep. Variable- Amount of Plant growth
Constants- Amount of soil, amount of water added to the plant, amount of sunlight
Control Group- Plant C (b/c it doesn’t have any fertilizer, so the student is seeing
how much the plant would grow normally- without fertilizer)
Work and Machines - What Is Work?
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a what or how question for
each heading. As you read, write answers to your questions.
Question
What is work?
Answer
Work is done when an object
moves in the same direction
in which the force is exerted.
How can you calculate
work?
Work = Force X Distance
What is power?
Power is the rate at which
work is done.
Work and Machines - What Is Work?
Calculating Power
Practice Problem
A crane lifts an 8,000-N beam 75 m to the top of a
building in 30 seconds. What is the crane’s power?
20,000 W or 20 kW
Work and Machines - What Is Work?
Links on Work
Click the SciLinks button for links on work.
Work and Machines
End of Section:
What Is Work?
Work and Machines
Noggin Knocker Calculations
Work and Machines
Learning Objectives
1.
Explain how machines make work easier.
• Increasing force, Increasing distance, Changing direction
2.
Determine the mechanical advantage of a machine (relative to 1).
3.
Calculate the efficiency of a machine.
Work and Machines - How Machines Do Work
Input and Output Forces
Examine the input and output
forces for a shovel.
The input force is also called
the applied force.
Work and Machines
Rise of the Machines Activity
In your lab notebook (this is not a FULL lab write-up):
1. Determine which of the following are machines: ramp, pliers,
screwdriver, baseball, ruler, coat zipper, paper, tweezers, gear
system of a bike.
2. For the ones that are machines, determine the input (or
applied) force and output force for each by drawing a
diagram of the machine with the input and output force labeled.
Work and Machines
Diagrams- Ramp & Pliers
Work and Machines
Diagrams- Screwdriver & Coat Zipper
Work and Machines
Diagrams- Tweezers & Bike
Work and Machines - How Machines Do Work
What Is a Machine?
A machine makes work easier by
changing the amount of force
you exert, the distance over
which you exert your force, or the
direction in which you exert your
force.
Examples:
1. Increasing Force- Turning the
knob to turn the hose on
2. Increasing Distance- Riding a
bike in high gear (you go farther
as you pedal)
3. Changing Direction- Lifting
weights using a pulley
Work and Machines
Rise of the Machines (Part 2)
Determine if the machine increases the force, increases the distance, or
changes direction: ramp, pliers, screwdriver, coat zipper, tweezers, gear system of
a bike, seesaw, & putting up a flag on a flag pole.
Ramp- Increases force (output force is greater than the input force of pushing an
object up a ramp)
Pliers- Increases force (output force>input force)
Screwdriver- Increases force (output force>input force)
Coat Zipper- Increases force (input force is low compared to the output force
pushing outward)
Tweezers- Increases distance (shorter distance when pinched in the middle causes
to ends to move further inward)
Bike Gears- Increases distance (bike in high gear- more force to pedal but you go a
greater distance)
Seesaw & Flag pole- Changing directions (pull/push downward & the flag or other
side of the seesaw goes up)
Work and Machines
Noggin Knocker Diagrams
Work and Machines
Which of the following is a simple machine?
A.
B.
C.
D.
Diagram 1
Diagram 2
Diagram 3
Diagram 4
Work and Machines
The force you apply when you first use a machine is
called the
A.
B.
C.
D.
Output force.
Input or Applied force.
Inner force.
Jedi Knight force.
Work and Machines
Machines make work easier by
A.
B.
C.
D.
Increasing the force.
Increasing the distance.
Changing directions.
All of the above.
Work and Machines
Which of the following machines USUALLY causes
a change in direction?
A.
B.
C.
D.
pulleys
screws
ramps
tweezers
Work and Machines
Which of the following increases the force?
A.
B.
C.
D.
A bike in high gear compared to lower gears
tweezers
screwdriver
A pulley
Work and Machines
Which of the following increases the distance?
A.
B.
C.
D.
Pliers & screwdrivers
Flagpoles and weight pulleys
Seesaws
Hockey sticks, brooms, & shovels
Work and Machines
Which of the following is true about why a steering
wheel connected to an axle is used in vehicles?
A. More force on the steering wheel is needed over a
shorter distance to make the vehicle turn.
B. Less force on the steering wheel is needed over a larger
distance to make the vehicle turn.
C. More force on the steering wheel is needed over a larger
distance to cause the vehicle to turn.
D. Less force on the steering wheel is needed over a shorter
distance to cause the vehicle to turn.
Arrows are not force
arrows!
Work and Machines
Learning Objectives
1. Calculate the mechanical advantage of a machine.
• Output Force/Input Force, Relative to 1 (Less than 1, Equal
to 1, Greater than 1)
Work and Machines - How Machines Do Work
Input and Output Work
The amount of input work done by the
gardener equals the amount of output
work done by the shovel.
Mechanical Advantage of a machine =
output force/input force
Work and Machines - How Machines Do Work
Mechanical Advantage
The input force and output force
for three different ramps are
shown in the graph.
Work and Machines - How Machines Do Work
Mechanical Advantage
Reading Graphs:
What variable is plotted on
the horizontal axis?
Input force
Work and Machines - How Machines Do Work
Mechanical Advantage
Interpreting Data:
If an 80-N input force is
exerted on Ramp 2, what is
the output force?
400 N
Work and Machines - How Machines Do Work
Mechanical Advantage
Interpreting Data:
Find the slope of the line for
each ramp.
Ramp 1: 10; Ramp 2: 5;
Ramp 3: 2
Work and Machines - How Machines Do Work
Mechanical Advantage
Drawing Conclusions:
Why does the slope represent
each ramp’s mechanical
advantage? Which ramp has the
greatest mechanical advantage?
The slope of each ramp’s graph
equals the change in output
force divided by the change in
input force. This is the formula
for mechanical advantage. Ramp
1 has the greatest mechanical
advantage.
Work and Machines
Noggin Knockers
Work and Machines
Mechanical Advantages of Ramps
Goal: Determine the mechanical advantage for various types of inclined
planes (ramps) via M.A. = Fo/Fi
Hypothesis: For the inclined planes, determine if you believe the
mechanical advantage will be greater than 1, equal to 1, or less than 1.
Explain why you predict this based upon how the machines work and the
equation for M.A.
Background:
• Output force = the ____________ of the object in N.
• Since the ramps have a rough surface, you must subtract the _______
force from the measured force up the ramp to obtain an accurate force
reading!
Procedure (Organize your results in a Table- on the next slide):
1. Determine the input force (Measured Force – Frictional force) and output
force for 3 different steepnesses of the ramp.
2. Calculate the mechanical advantage for the 3 ramp setups.
Work and Machines
Data Table & Conclusions
Machine/Setup
Output Force
Fo
(Weight in N)
Input Force
Fi
For the ramp: Measured
force – frictional force
(N)
Mechanical
Advantage
(Fo/Fi)
Ramp- slightly steep
Ramp- mid-steepness
Ramp- high steepness
Conclusions (answer in complete sentences):
1. Which ramp had the greatest mechanical advantage? Explain why.
2. Did any setup have a mechanical advantage less than 1? Explain why or
why not. Hint- Use the M.A. equation & the terms input & output force.
3. For the following M.A.’s, determine which one corresponds to the
machine that increases force: 0.6, 2.0, & 1.0.
Work and Machines

Mechanical Advantage of a Fixed Pulley
After the Conclusions from the previous experiment (Mechanical Advantages of
Ramps), record your data and conclusions for the M.A. of a pulley.
Background: The output force (once again) = the _________ in N.
Setup: Tie a long piece of string to the force sensor hook. Next, tie the untied end of
the string to the rubber band around the weights. Determine the output force.
Then untie the string and thread it through the pulley track. Tie it to the weights.
Results:
1. Measure the input force by pulling the force sensor down (which should pull the
weight up) and measure the force required to lift the weights.
2. Calculate the mechanical advantage.
Conclusions:
1. Was the mechanical advantage close to 1? If so, then explain why in terms of
the input force compared to the output force.
2. So if the M.A. = about 1, then the machine probably makes work easier by which
of the following: increasing the force, increasing the distance, or changing
direction.
3. Based upon the M.A. (relative to 1) of a machine that increases force and the
M.A. (relative to 1) of a machine that changes direction, what would the M.A. be
(relative to 1) for a machine that only increases distance?
Work and Machines
Mechanical Advantage of 3rd Class Lever (Broom)
Goal: Determine the M.A. of a 3rd class lever with a ruler and the
force sensor.
Procedure/Results:
1. Push with some force on the ruler in the middle while the
middle part is on the force sensor plunger or hook. Record this
input force.
2. Next, place the end of the ruler on the force plunger or hook
while still pushing with the SAME AMOUNT OF FORCE in the
MIDDLE of the ruler. Record this output force.
3. Calculate the Mechanical Advantage.
Conclusion: So, machines that increase distance (like a 3rd class
lever such as a broom) will have a M.A. ________ than 1.
Work and Machines
Mechanical Advantage of Machines
Procedure (For increasing force, think about you trying to do the work with
your hand instead of the machines):
In a table, record the input force relative to the output force, the
mechanical advantage (relative to 1), and whether the machine
increases force, increases distance, or changes direction for….
–
A fixed pulley (like a flagpole)- From the previous Pulley Activity
–
A wedge (like a coat zipper or an ax)
–
A 3rd class lever (see p. 129, Figure 17, Last Expt. w/ a meter stick)
–
Wheel and axle (like a screwdriver)
–
A screw (a winding incline plane- Refer to the ramp experiment).
Work and Machines
Graphic Organizer Table for Machines
Type of Machine
Inclined Plane
(Ramp)
Fixed Pulley
Wedge
3rd class lever
Wheel & Axle
A screw
Increases Force,
Increases
Distance,
Changes
Direction
Output Force
(>, <, or =)
Input force
Mechanical
Advantage
relative to 1
(> 1, < 1, = 1)
Increases Force
>
>1
Work and Machines
Graphic Organizer Table for Machines
Type of Machine
Increases Force,
Increases
Distance,
Changes
Direction
Output Force
(>, <, or =)
Input force
Mechanical
Advantage
relative to 1
(> 1, < 1, = 1)
Increases Force
>
>1
Changes Direction
About =
=1
Increases Force
>
>1
3rd class lever
Increases
Distance
<
<1
Wheel & Axle
Increases Force
>
>1
A screw
Increases Force
>
>1
Inclined Plane
(Ramp)
Fixed Pulley
Wedge
Work and Machines
Conclusions/Notes (just list answers)
1. What types of machines (BOTH the type and whether it
increases force, increases distance, or changes direction) have
a M.A. greater than 1?
2. What types of machines have a M.A. equal to 1?
3. What types of machines have a M.A. less than 1?
4. Are machines that have a mechanical advantage less than 1
still useful? Explain how.
5. Are machines that have a mechanical advantage equal to 1 still
useful? Explain how.
Work and Machines - How Machines Do Work
Calculating Efficiency
You do 250,000 J of work to cut a lawn with a hand mower. If the
work done by the mower is 200,000 J, what is the efficiency of the
lawn mower?
What is the main force that will resist the motion of the parts
of a machine and cause the efficiency to be less than 100%?
FRICTION
What information have you been given?
Input Work (Winput) = 250,000 J
Output Work (Woutput) = 200,000 J
Work and Machines - How Machines Do Work
Calculating Efficiency
You do 250,000 J of work to cut a lawn with a hand
mower. If the work done by the mower is 200,000 J,
what is the efficiency of the lawn mower?
Plan and Solve
What quantity are you trying to calculate?
The efficiency of the lawn mower = __
What formula contains the given quantities and the unknown
quantity?
Efficiency = Output work/Input work X 100%
Perform the calculation.
Efficiency = 200,000 J/250,000 J X 100%
Efficiency = 0.8 X 100% = 80%
The efficiency of the lawn mower is 80 percent.
Work and Machines - How Machines Do Work
Calculating Efficiency
You do 250,000 J of work to cut a lawn with a hand mower. If the
work done by the mower is 200,000 J, what is the efficiency of the
lawn mower?
Look Back and Check
Does your answer make sense?
An efficiency of 80 percent means that 80 out of every 100 J of
work went into cutting the lawn. This answer makes sense because
most of the input work is converted to output work.
Work and Machines - How Machines Do Work
Calculating Efficiency
Practice Problem
You do 20 J of work while using a hammer. The hammer
does 18 J of work on a nail. What is the efficiency of the
hammer?
90%
Work and Machines
Real vs. Ideal Machines
Ideal machines would operate at 100% efficiency, while
real machines operate at less than 100% efficiency due to
friction.
Real Machine, < 100% Efficiency
Ideal Machine, = 100% Efficiency
Work and Machines
Homework: p. 121- 1b, 1c, 2b, 2c, 3b, 3c, & 4
(14 points for accuracy- 2 pts. per problem)
1b- Increase force, increase distance, or change direction
1c- Screwdrivers increases or multiplies the force to make work
easier (input force is over a greater distance- the handle turning &
the output force is over a shorter distance- the tip of the screwdriver)
2b- Mechanical Advantage = 1 for ONLY changing direction.
2c- M.A. = output force/input force = 80 N/40 N = 2
3b- Ideal machines operate with 100% efficiency.
3c- Real and ideal machines make work easier, but real machines
operate at under 100% efficiency due to friction.
4- Efficiency = (6 J/12 J) x 100% = 50%
Work and Machines
The force the machine does on an object is called
the ___________ force.
A.
B.
C.
D.
Output
Input
Applied
Same
Work and Machines
The output force divided by the input force is the
A.
B.
C.
D.
Efficiency of the machine.
Mechanical advantage of the machine.
Ratio of good to bad parts of the machine.
Only calculation that has to be greater than 1.
Work and Machines
Which of the following will have a mechanical
advantage = 1?
A.
B.
C.
D.
Shovel
Screwdriver
A fixed pulley
Broom or 3rd class lever
Work and Machines
If the output force is greater than the input force,
then the M.A. is
A.
B.
C.
D.
Less than 1 like a broom
Greater than 1 like a screwdriver
Equal to 1 like a fixed pulley
Greater than 1 like a broom.
Work and Machines
Which of the following is true about why a steering
wheel connected to an axle is used in vehicles?
A. More force on the steering wheel is needed over a
shorter distance to make the vehicle turn.
B. Less force on the steering wheel is needed over a larger
distance to make the vehicle turn.
C. More force on the steering wheel is needed over a larger
distance to cause the vehicle to turn.
D. Less force on the steering wheel is needed over a shorter
distance to cause the vehicle to turn.
Arrows are not force
arrows!
Work and Machines - How Machines Do Work
Calculating Efficiency
Practice Problem
Suppose you left your lawn mower outdoors all winter.
Now it’s rusty. Of your 250,000 J of work, only 100,000 J
go to cutting the lawn. What is the efficiency of the lawn
mower now?
40%
Work and Machines - How Machines Do Work
Identifying Main Ideas
As you read the section “What Is a Machine?” write the main
idea in a graphic organizer like the one below. Then write
three supporting details that further explain the main idea.
Main Idea
The mechanical advantage of a machine helps by…
Detail
Detail
Detail
changing the
amount of force
you exert
changing the
distance over
which you exert
your force
changing the
direction of the
force
Work and Machines - How Machines Do Work
Links on Mechanical Efficiency
Click the SciLinks button for links on mechanical efficiency.
Work and Machines
End of Section:
How Machines
Do Work
Work and Machines
New Year = Higher Expectations
1. There will not be any more clicker re-takes unless 1/3 of the class or more scores
below a 74%. In that case, those students who received a below a 74% will retake a similar but different quiz. If most of the students score below a 74%,
then the quiz will not count and the content will be re-taught, and a similar quiz
will be given. Also, I will still allow you to go back and change your answers after
you find out how many you missed on the quiz.
2. Expect the Noggin Knockers to be graded for accuracy now. So, make sure
these are complete and accurate before you ask to use the restroom or go
somewhere else. If you need more time, then raise your hand and let the teacher
know. Keep in mind, it’s not my responsibility if you forget your pencil.
3. I will NOT be reminding you to turn in past homework or assignments unless you
come and see me about the work you’ve missed. However, if you have work that
can still be turned in and you are not currently working on any assignment, then
you will be asked to complete the missing work.
4. Lastly, lab notebooks will be checked shortly after the last experiment is
performed for the physics unit, which will be within the next 3 weeks. A list of the
experiments will be provided before the lab notebook check. The lab notebook
check will be worth 35 points and is 20% of your overall grade.
Work and Machines
Noggin Knockers
Work and Machines
Learning Objectives
1. Describe the 6 types of simple machines including the
different pulley setups and different classes of levers.
2. Describe the mechanical advantage (relative to 1) for
each simple machine in terms of output vs. input
force.
Work and Machines
Pulley Demo (2 Pulley- Fixed and
Movable/Block & Tackle)
Output Force = the person’s ___________.
Note that every time a machine lifts/moves
an object, the object’s weight is the output
force.
Input Force = Person’s ________ on the
rope downward.
Results: Output force is (greater than, less
than, or equal to) the input force.
Conclusion: So, the Mechanical Advantage
of this pulley system and others with 2 or
more pulleys is (greater than, less than, or
equal to) 1.
Work and Machines - Simple Machines
Pulley
A pulley is a simple machine made of a grooved wheel with
a rope or cable wrapped around it.
Work and Machines - Simple Machines
Inclined Plane
An inclined plane is a flat, sloped surface.
Work and Machines - Simple Machines
Screws
A screw can be thought of as an inclined
plane wrapped around a cylinder.
Work and Machines - Simple Machines
Wedge
A wedge is a device that is thick at one end and tapers to a
thin edge at the other end.
Work and Machines - Simple Machines
Wheel and Axle
A wheel and axle is a simple machine made of two circular
or cylindrical objects fastened together that rotate about a
common axis.
Work and Machines - Simple Machines
Wheel and Axle
You can find the ideal mechanical advantage of a wheel and
axle by dividing the radius of the wheel by the radius of the
axle.
Work and Machines - Simple Machines
Levers
A lever is a ridged bar that is free to pivot, or rotate, on a
fixed point.
1st class lever
Work and Machines
Lever Experiment
Goal- Model the 3 classes of levers shown below & determine how they
make work easier by comparing the input or applied force to the output force
(weights = 2.8 N).
Results- Record the input force for the 1st class lever (left), 2nd class lever
(middle), and 3rd class lever (right). Calculate the M.A.
Conclusion- State which levers increased force by making the input force
lower than the output force (weight). Also, state which levers make work
easier by changing the direction of the force or by increasing the distance.
Work and Machines - Simple Machines
Levers
Levers are classified according to the location of the fulcrum
relative to the input and output forces.
Work and Machines
Identification of Real World Examples
Identify the following examples of simple machines as 1 of the 6
previously discussed (be specific with levers and pulleys):
1. Shoving a shovel straight into the ground
2. Regular Broom (not a push broom)
3. Steering system of a bike or car
4. Ramp or a screw
5. Wheelbarrow
6. Pliers
7. A construction crane
Work and Machines - Simple Machines
Simple Machines in the Body
Most of the machines in your body are levers that consist of
bones and muscles.
Work and Machines
More Simple Machines in the Body
Teeth- Wedges
Turn your forearm at the elbow- Wheel & Axle
Muscle used to raise your eyes- Pulley
Work and Machines - Simple Machines
Compound Machines
A compound machine is a machine that utilizes two or more
simple machines.
Work and Machines
If the input force for the lever below is 100 N, then
the out put force or load weight would have to be
A.
B.
C.
D.
Less than 100 N.
Greater than 100 N.
Equal to 100 N.
Equal to 0 N.
Work and Machines
For a 1st class lever to increase force, where must
the fulcrum or pivot point be?
A.
B.
C.
D.
Closer to the input force.
Closer to the output force.
Directly in the middle.
At the other end.
Work and Machines
If the weight of the load is 100 N, then which of the
following is a possible value for the input or applied
force?
A.
B.
C.
D.
50 N
100 N
150 N
200 N
Work and Machines
For a 3rd class lever (like a broom or hockey stick), if
the input force is 50 N, then which of the following
would be a possible output force?
A.
B.
C.
D.
100 N
75 N
50 N
25 N
Work and Machines
Your body includes several simple machines such
as
A.
B.
C.
D.
Teeth acting as wedges.
Eye raising via a pulley.
Rotating your forearm is an example of a wheel and axle.
Lifting an object up using your arm and bending your
elbow is an example of a lever.
E. All of the above are examples of simple machines in your
body.
Work and Machines
A machine composed of 2 or more simple machines
is a
A.
B.
C.
D.
Simpler machine.
Complex machine.
Compound machine.
Machine that operates at 100% efficiency.
Work and Machines
Homework: p. 135- 1a, 1b, 1c, 2b, 2c, 3a, & 3b
1a- Inclined plane, wedge, screw, wheel & axle, pulley, lever
1b- Door stopper = wedge; rake = 3rd class lever, windmill = wheel and
axle, slide = inclined plane
1c- Yes, your thump pivots where it’s attached to your hand or at the
knuckle, so it can act as a lever (like when you flick a coin). Note that if
you rotate your thump around, it can also act like a wheel and axle.
2b- Combine more fixed and movable pulleys, so there are more sections
of rope (higher M.A.)
2c- The length of an inclined plane is similar to the length around the
threads around the screw.
3a- 2 or more simple machines make up a compound machine.
3b- Multiply the M.A.’s of the simple machines that make up the
compound machine.
Work and Machines - Simple Machines
Previewing Visuals
Before you read, preview Figure 17. Then write two
questions that you have about the diagram in a graphic
organizer like the one below. As you read, answer your
questions.
Three Classes of Levers
Q. What are the three classes of levers?
A. The three classes of levers are first-class levers, second-class
levers, and third-class levers.
Q. How do the three classes of levers differ?
A. They differ in the position of the fulcrum, input force, and output
force.
Work and Machines - Simple Machines
Levers
Click the Video button to watch a movie about levers.
Work and Machines - Simple Machines
Pulleys
Click the Video button to watch a movie about pulleys.
Work and Machines
End of Section:
Simple Machines
Work and Machines
Graphic Organizer
Simple Machine
Mechanical Advantage
Inclined plane
Length of incline ÷ Height of incline
Ramp
Wedge
Length of wedge ÷ Width of wedge
Ax
Screw
Length around threads ÷ Length of
screw
Screw
Lever
Distance from fulcrum to input force ÷
Distance from fulcrum to output force Seesaw
Wheel and axle
Radius of wheel ÷ Radius of axle
Pulley
Example
Screwdriver
Number of sections of supporting rope Flagpole
Work and Machines
End of Section:
Graphic Organizer