Science 8
Unit D: Mechanical
Systems
Topic 1.1 Learner Outcomes
• Investigate and provide examples of
mechanical devices used in the past to
meet particular needs
• Illustrate how a common need has
been met in different ways over time
• Identify components that operate as
simple machines
Section 1.1 – Simple Machines –
Meeting Human Needs
• Early machines were very simple devices.
– EX. Levers were used to pry rocks from the
ground.
– EX. Ramps were used to raise rocks to build walls.
• First machines used
humans or animals as
sources of energy.
Class Discussion
• What were the items in figure 1.1 use
for historically?
• How do the items work?
• What needs were they designed to
meet?
• What is the approximate time period
each were used in?
Moving Water Historically
• No pumps to move water, so people used gravity.
• Water stored in raised tanks, gravity caused it to
move through the pipes and to the community.
• Water and moved to raise tanks by water wheels
(sakia)
– a series of buckets attached to a long rope, which is
draped over a large wheel
•
Animals turned the wheel, which raised the
buckets of water.
Sakia
Moving Water Historically
• Archimedes made a more efficient way
by developing the Archimedes screw.
– Moves water by moving a screw.
• Still used today with a grain auger.
Archimedes Screw
Simple Machines
• Simple machines – tool or device made
up of one basic machine
• Every machine performs at least one of
these functions.
• The machine may:
–
–
–
–
Change the direction of a force
Multiply the speed or distance
Transfer the force from one place to another
Multiply force
Simple Machines
• Make a chart like the one provided in
the book on page 261 until it in as we
go.
Your chart should look
something like this (page 261)
Simple
Machine
Lever
Inclined Plane
Wedge
Screw
Pulley
Wheel and
Axel
Advantage
Disadvantage
1. Lever
• Rigid bar or plank that rotates around
a fixed point called a pivot or fulcrum.
– ADV: lever are used to reduce force
needed to carry out a task
– DISADV: to move a large load with a lever,
you must move a greater distance than
the load does
Lever
Lever Video
3 Types of Levers
• First class lever – fulcrum is between the
load and the point where effort is exerted
– EX. See saw, pry bar
• Second class lever – load is between the
effort and the fulcrum (fulcrum and the effort
are at the opposite ends of the lever)
– EX. Wheelbarrow
• Third class lever – effort between the load
and the fulcrum
– EX. Arm, hammer
3 Types of Levers
GOOD FOR:
Moving heavy
loads
EX. Crowbars and
pliers
GOOD FOR:
Lifting heavy
objects
EX.
Wheelbarrow
GOOD FOR: Gaining
speed
EX. Hammer, your arm
Three Classes of Lever Video
2. Inclined Plane
• Makes it possible to lift heavy objects using
smaller force
– Also called a ramp
• ADV: Uses a much smaller amount of force
than if you did not use the ramp.
• DISADV: Have to exert a force over a larger
distance
• DISADV: Often only used over small inclines –
the steeper the ramp, the harder it is to
control the object.
– EX. Wheelchair access ramps
Inclined Plane
Inclined Plane Video
Inclined Plane Online Gizmo
• LearnAlberta
– Username: LA389
– Password: 9489
• Ant on a Slant
– Try activity and answer the multiple choice
questions afterwards.
– Give Ms. Benard your score.
3. Wedge
• Similar to the inclined plane but used in a
different way
• Wedge machine is forced into an object.
• ADV: Wedge increases the force that you apply on
the object.
• Press on wide edge of wedge to exert a force on
the narrow end to split an object apart
• DISADV: Wedge only pushes object apart (unlike a
ramp which can be used to move objects up or
down)
– EX. Knives and axes
Wedge
Wedge Video
4. Screw
• Cylinder with the groove cut in a spiral
on the outside.
• Helps to increase the force you use
• Penetrates materials was little force
• Used to convert rotational motion to
linear motion (grain auger)
• Moves objects slowly.
Screw
Screw Video
5. Pulley
• Consists of wire, rope or cable moving
on grooved wheel
• Pulleys made of one or more wheels
• Pulleys can be fixed in place or moveable
• Pulley systems can be used to:
– Reduce effort
– Increase speed
– Change direction
Pulley
Pulley Video
Pulley Online Gizmo
• LearnAlberta
– Username: LA389
– Password: 9489
• Pulleys (Piano, Armchair)
– Try activity and answer the multiple choice
questions afterwards.
– Give Ms. Benard your score.
6. Wheel and Axel
• Combination of two wheels of different
diameters that turn together
• A longer motion on the wheel produces a
shorter more powerful motion at the axel
– Force advantage
– Must turn more on the larger wheel to apply
the force
– EX. Steering wheel and steering column
Wheel and Axel
• If force is applied to the axle and the
load on the wheel, you can increase the
speed.
– Speed advantage
– Must apply a large force to move the load
– EX. Bicycle
Wheel and Axel
Wheel and Axel Video
Wheel and Axel Online Gizmo
• LearnAlberta
– Username: LA389
– Password: 9489
• Wheel and Axel
– Try activity and answer the multiple choice
questions afterwards.
– Give Ms. Benard your score.
Video Review Quiz
http://www.msichicago.org/fileadmin/A
ctivities/Games/simple_machines/
Assignment
• Complete Questions 1-4 on
page 268
Topic 1.2 Learner Outcomes
• Describing the overall function of the
device
• Describing the contribution of individual
components or subsystems to the overall
function of the device
Section 1.2 – The Complex
Machine
• Complex machines – a system where simple
machines all work together
• System – group of parts that work together
to perform a function
– Usually a complex machine
– EX. Bicycle
• Subsystem – group of parts that performed
specific functions within a system
– Usually a simple machine
– EX. Pedal on the bicycle (lever)
• Do give it a try, page 271
• Complex machines move objects by
transferring energy from one source
to the object.
• Subsystems that transfer force are:
1. Linkages
2. Transmissions
1. Linkages
• Belt or chain to directly transfer energy from
energy source to an object
– EX. Bicycle chain
• You (the energy source) move your energy
to the bicycle wheels (objects you want to
move) by pedaling. Pedaling moves the chain
which moves the bike tires.
• Energy source Linkage  Object to move
• High tension belts can also be used
– EX. In a car motor
Linkages
2. Transmissions
• Special types of linkage
• Transfer the energy from the engine to the
wheels in large vehicles such as cars and
trucks
– Used to move much larger loads (transfers more
force)
– Contains many gears
– Low gear = move slowly
– High gear = moves quickly
Transmissions
Gears
• Pair or series of wheels with teeth
interlinked
• When they rotate, one gear wheel
transfers turning motion and force to the
other.
– Larger gearwheel moves more slowly than
the smaller gearwheel, but it rotates with
a greater force.
• EX. Car
– Gears also used to change the direction of
motion
• EX. Egg beater
• Gears are important because they control
the transfer of energy from one source
to another.
– EX. Rider to the bike tires
– EX. Car engine to car tires
Gears
https://www.youtube.com/watch?v=M8ZEJTNW3OM
http://www.smartkit.com/s5042/connect-it-gear-game/
http://illuminations.nctm.org/Activity.as
px?id=3549
Gears
• Driving gear – force applied from outside
• Driven gear (or follower gear) – force comes
from another gear
•
• Gears affecting speed:
– If the driving gear is larger than the driven gear, the
turning speed increases.
– These are called multiplying gears.
– If the driving gear is smaller than the driven gear, the
turning speed decreases.
– These are called in reducing gears.
Driving and Driven Gears
Multiplying Gears
Reducing Gears
Car Transmissions
• 1st gear: driving gear is smaller than
driven gear
• 2nd gear: approximately same size
• 3rd gear: driving gear is larger than
driven gear
Assignment
• Complete Questions 1-5 on
page 276
Topic 1 Review
• Complete Questions 1-5 on page 277
Topic 2.1 Learner Outcomes
• Analyze mechanical devices to determine
speed ratios and force ratios
• Build or modify a model mechanical
system to provide for different turning
ratios between driving and driven shaft,
or to achieve a given force ratio
• Compare theoretical and actual values of
force ratios, and proposed explanations
for discrepancies
Section2.1 – Machines Make
Work Easier
• Machines making working easier by
increasing the amount of force exerted on
an object.
Mechanical Advantage
• Mechanical advantage – the amount by which a
machine can multiply a force (also called force ratio)
• Input force – the force applied to the machine
• Output force – the force the machine applies to the
object
• EX. Lifting a car with a lever (log):
– Person pushing down on the log is the input force.
– Machine which has a mechanical advantage is a lever.
– Short end of a lever which lifts the car is the output force.
 OUTPUT > INPUT
Mechanical Advantage
• Forces are always measured in Newtons
(N).
Mechanical Advantage = Output Force
Input Force
MA = Output force  Input Force Foutput
 
MA  F
input
How to Problem Solve
1. Write out the formulas you will need.
2. Write out the variables in the question,
including the ones you need to find.
3. Plug the variables into the formula.
Example 1:
• It takes 45 N to lift a 180 N box with a pulley. What
is the mechanical advantage of the pulley?
• Step 1: Write out your formula.
• Step 2: Write out your variables.
– Foutput =
– Finput =
– MA =
Foutput
 
MA  F
input
 this is the one we need to find
• Step 3: Plug the variables into the formula.
Example 2:
• It takes 65 N to move a 400 N car up in inclined
plane. What is the mechanical advantage of the
inclined plane?
• Step 1 = ?
• Step 2 = ?
– Fo =
– Fi =
– MA =
• Step 3 = ?
Foutput
 
MA  F
input
Example 3:
• A lever has a mechanical advantage of 5 and is used to lift a 45
N box. What is the force needed to lift the box?
• Step 1: Formula
•
•
•
•
Step 2: Variables
Fo =
Fi =
MA =
• Step 3: Plug in the
numbers
Foutput
 

MA
Finput
Complete the Mechanical
Advantage Practice Questions
• Make sure to follow your 3 steps for each
question.
Speed Ratio
• Speed measures the distance an object
travels in a given amount of time
• Speed ratio – a measure of how the speed
of the object is affected by a machine
Speed Ratio
Speed Ratio = Input Distance
Output Distance
SR = dinput
doutput
dinput
 
SR  d
output
Example 1:
• If you are using a pulley to move a box and you move 4
meters and the box only moves 1 meter, what is the
speed ratio?
• Step 1: Write out your formula.
dinput
• Step 2: Write out your variables.
– doutput =
– dinput =
– SR =
 
SR  d
output
• Step 3: Plug the variables into the formula.
This means that the input
force (you) moves
____________ times faster
than the output force (box).
Example 2:
• In order to climb a mountain, a car must drive 65 m on a
curved inclined plane in order to get only 10 m up the
side of the mountain. What is the speed ratio?
• Step 1: Formula
dinput
• Step 2: Variables.
– doutput =
– dinput =
– SR =
• Step 3: Substitute variables.
 
SR  d
output
Complete the Speed Ratio
Practice Questions
• Make sure to follow your 3 steps for each
question.
NOTE:
• Machines will multiply force at a cost,
which is speed. If a machine is going to
do work, you must move farther than the
load actually does.
Mechanical Advantage Less
Than 1
• If a mechanical advantage is less than 1, it means that
the machine does not require a large output force.
Ex. A bicycle rider applies an input force of 650 N to the
pedals which results in an output force of 72 N.
MA = Fout/Fin
=
=
• This output force causes the bicycle to move much
faster than the rider could walk on their own.
Comparing Mechanical
Advantage to Speed Ratio
• In calculations, we often find the
mechanical advantage to equal the speed
ratio, but in real life, this does not occur.
WHY???
• Friction – a force that opposes motion
• Rough surfaces cause more friction than smooth
ones.
• Friction creates heat (use fans and lubricants to
reduce)
• Extra force is needed to overcome friction when
you move an object.
• EX. Pushing a box up a ramp – must push
harder when there is more friction.
• When you need a stronger force to
overcome friction:
– Mechanical advantage decreases
– Speed ratio remains unchanged (distance
measured stays the same) – represents ideal
mechanical advantage (with no friction)
Efficiency
• Measurement of how well a machine or
device uses energy
• More energy lost (heat), the less efficient a
machine is.
• Efficiency is a percentage %
Efficiency Calculations
• Efficiency (%) = MA x 100 %
SR
Example 1:
• If a pulley has a speed ratio of 3 and a mechanical
advantage of 2, what is the efficiency of the
pulley?
• Step 1: Write out your formula.
• Step 2: Write out your variables.
– Efficiency =
– MA =
– SR =
• Step 3: Plug the variables into the formula.
Example 2:
• A car engine has a speed ratio of 20 and a
mechanical advantage of 3, what is the efficiency?
• Step 1: Formula.
• Step 2: Variables.
– Efficiency =
– MA =
– SR =
• Step 3: Substitute variables.
Complete the Efficiency Practice
Questions
• Make sure to follow your 3 steps for each
question.
Assignment
• Complete Questions 1-5 on
page 286
Topic 2.2 Learner Outcomes
• Compare theoretical and actual values of
force ratios, and propose explanations for
discrepancies
• Identify work input and work output in
joules for a simple machine or mechanical
system
Section2.2 – The Science of
Work
• Brainstorm all the times you did work
today.
Work
• Work – done when a force acts on an object to
make the object move.
– Circle all of your ideas above that were truly work
(in the scientific sense).
• Movement is necessary for work to be done.
MOVEMENT AND FORCE MUST BE
GOING IN THE SAME DIRECTION!
– EX. Trying to move a car requires a lot of force, but
if it does not move, no work has been done.
Work or Not?
• According to the
scientific definition,
what is work and what
is not?
– a teacher lecturing to her
class
– Students writing down
calculations on a piece of
paper.
– a mouse pushing a piece of
cheese with its nose across
the floor
89
90
What’s work?
• A scientist delivers a speech to an audience of
his peers.
– No
• A body builder lifts 350 pounds above his
head.
– Yes
• A mother carries her baby from room to room.
– No
• A father pushes a baby in a carriage.
– Yes
• A woman carries a 20 kg grocery bag to her
car?
– No
91
Work = Force x Distance
• W = Work (Joules)
• F = Force (Newtons)
• d = distance (meters)
W
 
F  d
NOTE: Newton x meter = Joule (J)
We measure work in Joules.
Work Example 1:
• You pick up your books off of the floor. How
much work did you do if you have exert a force of
50 N to lift the books and you lift them 0.5 m high?
• Step 1: Write out your formula.
• Step 2: Write out your variables.
– d=
– F=
– W=
• Step 3: Plug the variables into the formula.
Check for Understanding
Two physics students, Brian and Bonnie, are
in the weightlifting room. Bonnie lifts the
50 kg barbell over her head (approximately
0.60 m) with a force of 100 N; Brian lifts a 5
kg barbell the same distance over his head
with the force of 75 N.
Which student does the most work?
94
95
Explain who is doing more work and why:
a bricklayer lifting, carrying and placing
bricks on the wall of a building being
constructed, or a project supervisor
observing and recording the progress of
the workers from an observation booth.
How much work is done in pushing an
object 7.0 m across a floor with a force of
50 N and then pushing it back to its
original position?
Complete the Work Practice
Questions
• Make sure to follow your 3 steps for each
question.
• Energy and work are related.
– Without energy, we would not be able to do
work.
– Energy provides the force which has the
ability to move objects.
Work and Machines
• Different simple machines help us to do
work.
• We use machines so we don’t have to exert as
much force to do the same amount of work.
• Work can be INPUT or OUTPUT
– Work input is the work done by what is using
the machine (you).
– Work output is the work that the machine does.
Example
• A student pushes their friend in a wheelchair up an inclined plane. They
must exert a force of 320 N for a distance of 5 m. The student in the
wheelchair exerts a force of 800 N downward while sitting in the wheelchair
and is lifted 2 m off the ground using the inclined plane. What is the work
input and work output?
• Step 1: Work Input
• Step 2:
– dinput=
– Finput =
– Winput =
• Step 3:
Work Output
doutput=
Foutput =
Woutput =
• The work input and output are the same,
but the machine has simply made it an
easier task.
– Work input and output are not always equal
– This is due to friction
– Friction affects a machine’s efficiency
Complete the Work Practice
Questions
• Make sure to follow your 3 steps for each
question.
Work and Friction
• We can calculate a machine’s efficiency using
work input and work output.
Efficiency = Woutput x 100 %
Winput
REMEMBER that efficiency is a percentage (%).
Example
• If the work input of a device is 1600 J, and the work
output is only 1200 J, what is the efficiency of the
device?
• Step 1: Formula.
• Step 2: Variables.
– Woutput =
– Winput =
– Efficiency =
• Step 3: Substitute variables.
Complete the Work Efficiency
Practice Questions
• Make sure to follow your 3 steps for each
question.
Assignment
• Complete Questions 1-9 on
page 292
Topic 2.3 Learner Outcomes
• Describe fluid pressure qualitatively and
quantitatively, by:
– Explaining how forces are transferred in all
directions
– Describing pressure in units of force per unit area
• Describe how hydraulic pressure can be used
to create a mechanical advantage in a simple
hydraulic jack
• Describe and interpret technologies based on
hydraulics and pneumatics
Section2.3 – Hydraulics
• Hydraulic system – uses liquid under pressure to move
loads. It increases the mechanical advantage of levers in
machines.
• Pascal’s Law – pressure applied to an enclosed fluid is
transmitted equally in all directions throughout the fluid.
Pressure = Force  Area
P= F
A
• Pressure is measured in Pascals (Pa).
F
 
P  A
• Hydraulic systems use a combination of two
pistons attached to either end of a cylinder or
flexible pipe.
• Input piston – first piston which is used to
apply force to the fluid (create pressure on
fluid)
• Output piston – second piston which is
moved due to the force applied to the input
piston.
Mechanical Advantage
• When you push on a smaller piston, it
presses on the fluid to raise a larger output
piston, which lifts the object.
– The force is transferred from one piston to the
other.
• We can calculate mechanical advantage if we
know the input force and the output force.
REMEMBER
MA = Fout
Fin
Example
• If the input force is 20 N and the output force is 500 N,
calculate the mechanical advantage of the hydraulic
system.
• Step 1:
• Step 2:
– Fo =
– Fi =
– MA =
• Step 3:
*** This is a very
large mechanical
advantage!
Complete the Hydraulics
Mechanical Advantage Practice
Questions
• Make sure to follow your 3 steps for each
question.
Assignment
• Complete Questions 1-4 on
page 300
Topic 2 Review
• Complete Questions 1-6 on page 303
Topic 3.1 Learner Outcomes
• Evaluate the design and function of a
mechanical device in relation to its
efficiency and effectiveness, and identify
its impacts on humans and the
environment
• Develop and apply a set of criteria for
evaluating a given mechanical device, and
defend those criteria in terms of relevance
to social and environmental needs
Section 3.1 – Evaluating
Mechanical Device
• Mechanical devices are evaluated for
improvements.
Criteria to Evaluate a Device
• Complete questions on page 305 – with a
partner, list the features that you would
like to have in a bicycle.
• Write down your list on the chart paper
provided.
Criteria to Evaluate a Device
• This list of features are criteria for
evaluating the bicycle’s design.
• Criteria are features to consider when
looking at a mechanical device’s design.
• Often criteria include purpose of device
and cost.
Factors to Consider When
Evaluating a Device:
• Efficiency – how quickly and easily a
machine helps you to do a task
• Effectiveness – how well a machine does
its job
• Function – what the device is supposed to
do
• Design – physical form of the device that
makes it usable
• Environment – influences the design and
function of a device. We also evaluate
what effects the device has on the
environment.
EX. Comparing Bike Design
• A one speed bike is effective in carrying you from
point A to point B, but a 21 speed bike is more
efficient in doing this task.
• When evaluating a mechanical device, you look at
a combination of efficiency and effectiveness.
• A bicycle’s function is to carry a person from
point A to point B, but with different designs,
they can perform different functions such as
mountain biking and speed racing.
• We evaluate devices to see if they suit our needs
and to see how it can be improved.
Criteria for Evaluation
• Ask these questions:
– Is it effective?
– Is it efficient?
– Does it function properly?
– Is the design usable?
– What effect does it have on the environment?
Assignment
• Complete questions 1-4 on pg. 314.
• Complete the Try This At Home Activity
Topic 3.2 Learner Outcomes
• Illustrate how technological development
is influenced by advances in science, and
by changes in society and the environment
Section 3.2 – Technology
Develops through Change
• Technology will develop over time. An
example is how the pop can changed due
to:
– Human needs
– Environmental needs
– New materials
– New technology
– New methods of production
– Failure
• Trial and error are a large part in
technology development.
• What changes do you think contributed to
the changed in the sewing machine?
Changing Society – Changing
Technology
• When scientists, engineers, and inventors learn
more about science, technology develops.
• Some technology develops from research that was
not even intended for that device.
• New technology also results from changes to
human society.
– EX. Robots to replace people in the workplace – now
needed because people are demanding higher wages
and better working conditions.
• Changes in the environment results in
new technology.
• People are observing changes in the
environment and realize we need to
prevent more damage.
– EX. Recycling strategies
– EX. Hybrid cars
Assignment
• Complete questions 1-4 on page 320.
Topic 3 Review
• Complete Questions 1-4 on page 321
Unit Review Questions
• Complete questions 1-35 on pages 327 to
329, as a review before your Unit Test.