Work and Machines
Table of Contents
What Is Work?
How Machines Do Work
Simple Machines
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 - 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
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
Noggin Knockers
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
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
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.
Work.
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: Modern Warfare 3
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
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
Noggin Knockers
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
Learning Objectives
1. Explain how machines make work easier.
• Lowering the applied force and/or 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, draw a diagram of the machine
and draw the input (or applied) force and output force
arrows.
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
LOWERING the amount of force
you exert (by increasing the
distance over which you exert
your force), or the direction in
which you exert your force.
Examples:
1. Lowering the applied forceTurning the knob to turn the hose
on
2. Changing Direction- Lifting
weights using a pulley
Work and Machines
Rise of the Machines (Part 2)
Determine if the machine lowers the applied force OR changes
direction: ramp, pliers, screwdriver, coat zipper, seesaw, & putting up a flag
on a flag pole. Hint: If it’s difficult to use your hands for a task (making it so
you need to use the machine for a task), then that machine probably lowers
the applied force.
Ramp- lowers the applied force (output force is greater than the input force
of pushing an object up a ramp)
Pliers- lowers the applied force (output force>input force)
Screwdriver- lowers the applied force (output force>input force)
Coat Zipper- lowers the applied force (input force is low compared to the
output force pushing outward)
Seesaw & Flag pole- Changing directions (pull/push downward & the flag or
other side of the seesaw goes up)
Work and Machines
Which of the following is a simple machine?
A.
B.
C.
D.
E.
Diagram 1
Diagram 2
Diagram 3
Diagram 4
Diagram 5
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.
Lowering the initial effort required to do the work.
Lowering the applied force.
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
Saying mean things to someone stronger than you
ramps
tweezers
Work and Machines
Which of the following lowers the applied
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 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 show distance
traveled, not force!
Work and Machines
Suppose you are using a screwdriver, and the
output force is 100 N. Which of the following is a
possible applied force? Hint: Keep in mind how
this machine makes work easier and double check
to ensure your answer makes sense.
A.
B.
C.
D.
200 N
150 N
40 N
0N
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/applied force
M.A. = Fo/Fa
Work and Machines
Mechanical Advantages of Ramps
Goal: Determine the mechanical advantage for inclined planes (ramps) with
varying steepness by using M.A. = Fo/Fa
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 cart = 2.5 N.
Procedure (Organize your results in a Table- on the next slide):
1. Determine the applied force (by pushing the go-car up the ramp with the
force sensor) 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)
Applied Force
Fa
(N)
Mechanical
Advantage
(Fo/Fa)
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 applied force & output
force.
3. Based upon your data, determine which M.A. corresponds to the
machine that lowers the applied 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 fixed pulley.
Background: The output force (once again) = the _________ in N.
Setup: Tie a long piece of string to the force sensor hook. Make sure the weights
are not hanging and the string is loose with some slack. 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 applied force by pulling the force sensor down (which should pull
the weight up).
2. Calculate the mechanical advantage (Fo/Fa).
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: lowering the applied force OR changing direction.
Work and Machines
Mechanical Advantages of Machines
Procedure (In groups)
Record the following in your lab notebook with the title above.
Determine if the machine lowers the applied force OR changes the
direction of the force; then determine which is greater- the output or
the applied force; lastly, determine it’s M.A. relative to 1 (<, >, or =)
for…
–
Inclined Plane (a ramp)- Refer to the ramp experiment.
–
A fixed pulley (like a flagpole)- Refer to the Fixed Pulley experiment.
–
A wedge (like a coat zipper or an ax)
–
Wheel and axle (like a screwdriver)
–
A screw (a winding inclined plane)- Refer to the ramp experiment.
Work and Machines
Graphic Organizer (Table) for Machines
Type of
Machine
Lowers the Applied
Force OR Changes
the Direction of the
Force
Output Force
(>, <, or =)
Applied force
Mechanical
Advantage
relative to 1
(> 1, < 1, = 1)
Inclined Plane
(Ramp)
Lowers the applied
force
>
>1
Fixed Pulley
Changes Direction
About =
=1
Wedge
(ax, zipper)
Lowers the applied
force
>
>1
Wheel & Axle
(screwdriver,
doorknob)
Lowers the applied
force
>
>1
A screw
Lowers the applied
force
>
>1
Work and Machines
Input Work vs. Output Work
Ramp example containing data from the experiment:
Applied Force = 1.0 N
Input Distance = 1 m
Output force = 3.0 N
Output distance = 0.33 m
Input Work = 1.0 N x 1 m = 1 N x m or 1 J
Output Work = 3.0 N x 0.33 m = 1.0 J
Input Work = Output Work
without friction
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
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
The force the machine exerts on an object is called
the ___________ force.
A.
B.
C.
D.
Output
Input
Applied
Same
Work and Machines
The output force divided by the applied 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 or
applied 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
None of the above are completely true.
Work and Machines
The efficiency of a ramp is 76%. Why is it not 100%
since input work is supposed to equal output work?
A. The reaction force of the machine on the person causes this
difference.
B. It is 100%, the first statement is a lie!
C. Friction causes the output work to be less than the input work.
D. Gravity causes the output work to be less than the input work.
Work and Machines
Contrast real and ideal machines.
A. Real machines < 100% efficiency, while ideal machines =
100% efficiency.
B. Real Machines = 100% efficiency, while ideal machines <
100& efficiency.
C. Real Machines > 100% efficiency, while ideal machines =
100% efficiency.
D. Real Machines keep it real, while the only ideal machine
is my 8th grade science teacher.
Work and Machines
End of Section:
How Machines
Do Work
Work and Machines
Noggin Knockers/Hwk.- p. 113- 1c, p. 121: 1b, 1c, 2b,
2c, 3c 12 pts. total- 2 points each)
1- Rolling a bowling ball & kicking a football.
2- Screwdrivers lower the applied force (the amount of force or
effort you exert).
3- M.A. = 1
4- M.A. = 80 N/40 N = 2
5- Real Machines have less than 100 % efficiency due to friction.
6- (b) 70 N (applied force/force you exert on the ax should be less
than the output force/force the ax exerts on the piece of wood)
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. applied force.
(See Mechanical Advantages of Machines in your lab
notebook)
Work and Machines
Pulley Demo (2 Pulley- Fixed and
Movable/Block & Tackle)
Output Force = the object’s ___________.
Note that every time a machine lifts/moves
an object to a different location, the object’s
weight is the output force.
Applied 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
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- Draw and 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).
2nd
class
3rd class
1st class
Results- Record the applied force for each lever and calculate the M.A for
each class of lever.
Conclusion- State which levers lower the applied force and which levers
make work easier by changing the direction of the force. Are there any
levers that do both (lower the applied force and change the direction of the
force)? If so, which one(s)?
Work and Machines
Lever Experiment Extension (No lab write-up)
Goal- Determine how lifting a bunch of books
(with a heavy load weight) compares to
using a 1st class lever to lift the books.
Procedure
1. Lift the books and remember how much
force it felt like you were exerting.
2. Then repeat using a 1st class lever.
Results/Conclusions
Did the lever make it easier to lift the
books? If so, then how? Hint- Compare
your applied force using the lever to the
amount of force that it took to just lift the
books (output force/weight).
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 any levers):
1. Shoving a shovel straight into the ground
2. Steering system of a bike or car
3. Ramp or a screw
4. Wheelbarrow
5. Pliers
6. 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 output 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 lower the applied 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
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
Which of the following is an example of a
compound machine?
A.
B.
C.
D.
Using a meter stick as a 1st class lever
Fixed pulley
Ramp
Scissors
Work and Machines
Work & Machines Quiz Answers
1. C- pushing a box up a ramp (object moves in the direction
of the force)
2. E- lowering applied force and changing the direction of
the force
3. D- 100% machine efficiency (output work = input work)
4. A- output force greater than input force (M.A. = Fo/Fa; ex.3/1 = 3 which is greater than 1)
5. D- 3.0 (see example above- applied force is the lesser
force)
6. A- Equal to 1 (output force = input force; ex.- 2/2 = 1)
7. C- less than 10 N (Refer to Lever Expt.)
8. C- Smaller input force over a larger distance etc.
(Examine diagram)
9. B- 30 N (only force greater than 20 N, since Fo > Fa)
Work and Machines
Work & Machines Quiz Answers
10. B- pulley that changes the direction fo the force (pull
down and flag goes up)
11. A- Diagram 1 has the most pulleys
12. A- inclined plane (refer to notes)
13. B- screw (refer to notes)
14. B- Lever (hammer head is the pivot point/fulcrum)
15. D- Lever decreases the amount of force (AKA the applied
force) required to lift the load (Refer to Lever Expt.)
16. A- inclined plane (ramp) and wheel and axle (from
wheelchair)
17. C- Teeth (cut through food)
18. B- the human body (consists of levers- neck, foot, arm;
pulley- eye raising, wedges- teeth, etc.)
Work and Machines
Work & Machines Practice Quiz Answers
1. When a force is applied to an object and it moves in the same
direction as the force.
2. Friction
3. Applied force is lower for machines with M.A.’s greater than 1.
4. Greater than 5 N (because the applied is lower than the output force)
5. M.A. = 1, then that machine ONLY changes the direction of the force.
6. 1st class lever: lowers the applied force and changes the direction of
the force. 2nd class lever: lowers the applied force.
7. Applied force is less than 100 N (because the applied force is lower than
the output force/load weight).
8. A LOWER applied force is exerted over a GREATER distance (on the
wheel) while a larger output force is over a shorter distance (on the
axle).
Work and Machines
Work & Machines Practice Quiz Answers
9. Multiple pulleys result in a lower applied force (so it would be easier to
lift an object with a heavier weight)
10. (a) Ramp
(b) Screw
(c) Door stopper, knife, ax, teeth
(d) Doorknob, steering wheel, rotating your forearm
(e) Seesaw, pliers, scissors, lifting your head
(f) Wheelbarrow, door, lifting your heel
(g) Raising a flag on a flagpole, construction cranes, eye raising
11. A compound machine is 2 or more simple machines put together.
(examples include scissors, the human body, wheelbarrow)
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