Science 8 Unit D: Mechanical Systems. Topic 1.1 Learner Outcomes Investigate and provide examples of...

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.

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

Advantage Disadvantage

Lever

Inclined Plane

Wedge

Screw

Pulley

Wheel and Axel

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 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 LeversGOOD 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 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 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


• Pulleys (Piano, Armchair)– Try activity and answer the multiple


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


• Wheel and Axel– Try activity and answer the multiple


Video Review Quiz

http://www.msichicago.org/fileadmin/Activities/Games/simple_machines/



Assignment

• Complete Questions 1-4 on page 268


• 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. Linkages2. 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

Gearshttps://www.youtube.com/watch?v=M8ZEJTNW3OM

http://www.smart-kit.com/s5042/connect-it-gear-game/

http://illuminations.nctm.org/Activity.aspx?id=3549

https://www.youtube.com/watch?v=M8ZEJTNW3OM





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


Topic 1 Review



• 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


• Forces are always measured in Newtons (N).

Mechanical Advantage = Output Force

Input Force

MA = Output force Input Force

Foutput

MA Finput

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 =

• Step 3: Plug the variables into the formula.

this is the one we need to find

Foutput

MA Finput

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 Finput

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 RatioSpeed Ratio = Input Distance Output Distance

SR = dinput

doutput

dinput

SR doutput

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 2: Write out your variables.– doutput =

– dinput =

– SR =


dinput

SR doutput

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

• Step 2: Variables.– doutput =

– dinput =

– SR =

• Step 3: Substitute variables.

dinput

SR doutput

Complete the Speed Ratio Practice Questions


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 2: Write out your variables.– Efficiency = – MA =– SR =


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 =


Complete the Efficiency Practice Questions


Assignment



• 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.

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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

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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

Work = Force x Distance

• W = Work (Joules)• F = Force (Newtons)• d = distance (meters)

NOTE: Newton x meter = Joule (J)

We measure work in Joules.

W

F d

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 2: Write out your variables.– d= – F =– W =


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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?

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


• 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 Work Output

• Step 2:– dinput= doutput=

– Finput = Foutput =

– Winput = Woutput =

• Step 3:

• 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


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 =


Complete the Work Efficiency Practice Questions


Assignment



• 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.


• 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


Assignment


Topic 2 Review



• 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


• 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


Unit Review Questions

• Complete questions 1-35 on pages 327 to 329, as a review before your Unit Test.

Science 8 Unit D: Mechanical Systems. Topic 1.1 Learner Outcomes Investigate and provide examples of...

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