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KISS Resources for the Australian Curriculum - Science

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Topic 12.8P “Energy” PhotoMastercopyright © 2012 KEEP IT SIMPLE SCIENCEwww.keepitsimplescience.com.au

KEEP IT SIMPLE SCIENCEPhotoMaster Format

ENERGYYear 8 Physical Sciences

®

keep it simple science

Topic 12.8P

KISS topicnumber

Year level designation inNat.Curriculum

Science Understanding StrandB = Biological SciencesC = Chemical Sciences E = Earth & Space SciencesP = Physical SciencesTopic Outline

Efficiency of EnergyConversions

Conductors,Insulators& Circuits

EnergyConversions

LightEnergy

Types ofEnergy

ElectricalEnergy

Work,Machines &Efficiency

Conservationof Energy

HeatEnergy

SoundEnergy

What is this topic about?To keep it as simple as possible, (K.I.S.S. Principle) this topic covers:

TYPES OF ENERGYAn overview of the types of energy and how energy converts from

one form to another.

SOUND, LIGHT & HEATThe most familiar and important types of energy.

ELECTRICAL ENERGYAn introduction to electricity, including the basics of electrical circuits.

CONSERVATION OF ENERGYSimple idea, but one of the most important scientific principles.

WORK, MACHINES, EFFICIENCYEfficiency of energy conversions.

Revision of Simple Machines and the concept of “Work”.

ENERGY




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What is Energy? Energy is what causes things to change.

There are many different types of energy. Here are just a few:

Energy Type Changes CausedHEAT Change in temperature.

e.g. a stove causes food to get hot.

LIGHT Nerve changes in your eye which allowyou to see things, or chemical changesin the film in a camera.

SOUND Can cause vibrations in your ear whichallow you to hear.

ELECTRICITY Can cause a light bulb to glow and produce light, or a stove element to get hot and produce heat.

RADIO WAVES Can cause electrical vibrations in anantenna for reception of mobile phone, radio & TV programs.

NUCLEAR Energy in the nucleus of atoms which is released by an “atom bomb”, or in a nuclear power station.

An explosion like thisreleases Heat, Light and

Sound energy.

Two More Important Types of Energy

Two types of energy need special attention: (learn these especially!)

Kinetic Energy (KE)KE is the energy of a moving object. Itcauses the object to change its positionby moving.

If the moving object hits something, theKE can cause other changes, such as thedamage done when moving cars collide.

Potential Energy (PE)PE is energy stored in things, and notalways obvious or apparent. There are 3 types:

Gravitational PE is energy stored in anobject in a high position. The energy is notapparent until the object falls down due togravity. As it falls, the energy converts to KE.

Chemical PE is energy stored in chemicals. The energy is not apparent untila chemical change occurs which releasesthe energy. Chemical PE is stored in chemicals like candle wax (can burn torelease heat and light) or in a battery (canmake electricity) or in petrol (can make acar move with KE).

Elastic PE is energy stored in objectswhich have been stretched, compressed ortwisted out of shape. When released, theelastic PE is released, often causing some-thing to move with KE. e.g. When released, a stretched bow makesthe arrow fly.

Chemical PE (in rocket fuel) isconverting into KE (speed) and

Gravitational PE (height)



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Please completeWorksheets 1,2,3before going on.


Energy Conversions

Observing Energy ConversionsYou may be able to observe some energy conversions in the laboratory.

Why Learn about Energy?Energy is the basic stuff of the universe. It powers all living things, all

machines, the weather, the Sun... everything!

Whenever you use energy, it always converts into a different type of energy.

Examples

In a light bulb,

electrical energy light + heat

converts into

converts into

In a car,

Chemical PE in petrol KE of moving car

Anything falling due to gravity is converting energy:

If there was no air, a falling object would continue toaccelerate. However, these skydivers quickly reach

“terminal velocity” due to air resistance.

GPE KEGravitational Kinetic

Potential Energy Energy

converts into

GPE is now converting into (mainly) low-grade heat which is spreading out in their wake.

Hand-Powered Generator (above)

When you turn the handle, the KEdrives a generator which makeselectricity. The electrical energy

then makes light in the bulb.

Burning Candle

The wax containsChemical PE which

converts into light & heatenergies as the canle

burns.

Solar Fan

The solar-cells turnlight energy into

electricity.The fan turns

electricity into KE.




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Sound EnergyWhen you hear a sound, you are detectingthe energy of vibrations travelling throughthe air. These are sound waves.

In air, sound waves travel at about 330metres per second (m/s). This means theycan travel 1 km in 3 seconds.

The air doesn’t really go anywhere as thewaves pass through it. The air simplyvibrates back-and-forth.

Thestrings vibrate.

This causes the air tovibrate too. Waves ofvibration spread out

through the air... sound waves.

The air is called the “medium” for thesound waves... the substance it travelsthrough.

Sound can travel through many differentmediums, but cannot travel through “nothingness”... a vacuum. It must have asubstance to vibrate and carry the soundwaves.

Sound travels at different speeds in different mediums.

In water, it travels at about 1,500 m/s (1.5 km in 1 second) and can carry forhundreds of kilometres. The “singing” ofwhales can be heard by other whales 500 km away!

In a metal, sound travels at about 5,000 m/s. (That’s 5 km in 1 second!)

Experimenting With Sound Energy

Sound is a Vibration

1. Look closely at a plucked guitar string.You can see it is vibrating as it makes asound.

2. You might do this in class.

3. Gently touch the front of the speaker of aradio or music system. You can feel thevibrations as sounds are produced.

Vibrating tuning forkgently placed onto the

surface of water.

Look for signs ofvibration on thewater surface.

Sound Needs a MediumYour teacher might demonstrate this inclass.

When the bell-jar is filled with air, you canclearly hear the bell ringing.

When most of the air is pumped out, youcan barely hear it, but you can see that itis still ringing.

Sealed, glass “bell-jar”with electric bell or

buzzer inside.

Air can bepumped out by avacuum pump, orallowed back inthrough a valve.

Sound is a vibration moving through a substance. It cannot travel in a vacuum, but must have a medium.

Please completeWorksheet 4

before going on.




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Light Energy

Light is a form of energy which travels as waves. Unlike sound, light waves do NOT need a medium to travelthrough... in fact they travel best through a vacuum.

When you see light from the Sun, Moon or the stars it hastravelled to your eyes through the empty vacuum of outerspace.

Light can also travel through some substances such as air,water and glass. These substances which allow light topass through, are “transparent”. Substances that block light (such as metal or concrete)are said to be “opaque”.

Light travelsthrough

empty space

Light waves travel at the amazing speed of 300,000 kilometres per second. That’s the equivalent of going around the Earth 6 times in one second!

More About LightThunder and LightningWhen you see a flash of lightning,you are detecting light waveswhich travel so fast (“speed oflight” = 300,000 km/sec) that it isvirtually instantaneous.

The lightning also creates soundenergy ...“thunder”.

Being soundwaves, the

thunder travelsmuch slower.So, you hearthe thunder

after you seethe lightning,even though

they are created at the

same time.

If you count the seconds betweenseeing the lightning and hearingthe thunder, you can calculatehow far away it is.

Every 3 seconds = 1 km away.

Light’s “Family” of WavesLight is a very special type of energy because we candetect it with our eyes.

There are also many other types of energy which arewaves of the same type as light waves, but we cannot seethem.

Gamma Rays - dangerous nuclear radiations.

X-Rays - penetrating waves used for medical investigation.

Ultra-violet (U.V.) - rays from the Sun which cause tanning, sunburn & skin cancers.

Light - which our eyes can detect.

Infra-Red (I.R.) - waves which carry heat energy.

Microwaves - used in RADAR, communications & microwave ovens.

Radio waves - used for radio and TV broadcasts.

All these are waves of the same type, & travel through space at the“speed of light”. Please complete

Worksheet 5before going on.




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Heat EnergyWe cannot see or hear heat energy, but we can feel itbecause of receptors in our skin. Heat energy is responsiblefor the measurement we call “temperature”.

Heat energy can “flow” (or transfer) from a hotter zone to acooler zone in three ways:

Conduction Conduction is the main way that heat energy moves throughsolids, but heat can also conduct through liquids & gases.Some solid substances allow heat energy to flow throughquickly. These are said to be “good conductors” of heat.(example: metals)

Other substances are poor conductors because heat flows through them slowly. If theyare very poor conductors, they are called “insulators”. (examples: air, wool, plastics)

Convection Convection is the main way that heat energy moves throughliquids and gases. Hot fluid rises and flows in a “convection current”.

RadiationRadiation is the only way that heat energy can move through empty space, such as whenthe heat of the Sun reaches the Earth. Heat radiation is carried by Infra-Red waves (I.R.),which travel at the speed of light. I.R. waves can also travel through air & many othertransparent substances. Anything glowing “red-hot” is giving off I.R. heat radiation.

More About Heat EnergyCelsius Temperature Scaleis named after the Swedish scientist who invented it.

Insulating AnimalsMost mammals and birds keep their bodies at a constant temperature close to

40oC, but many are quite comfortable infreezing conditions. How come?

Its all about insulation to slowdown heat loss.

This bear stayswarm because of itsinsulating fur coat.

Fur doesn’t insulatewhen wet, so thissealion needs alayer of blubber

(fat) under its skin.

The temperature at which water boils is

defined as 100oC. The temperature at which water freezes

to ice is defined as 0oC. 1oC is simply 1/100 of the

scale in between.

37oC is normal body temperature for humans.

There is really no such thing as “cold”.Coldness is just less heat energy. Evenif something has a temperature below

zero, it still contains some heat energy.

However, if we feel uncomfortable dueto lack of heat, we say we are “cold”,

and wear insulating clothing to trap our body heat.




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Please complete Worksheets 6 & 7before going on.

Experimenting With Heat Energy

Investigating ConductionAn experiment you may have done, orseen demonstrated:

This allows you to compare the rate of heatconduction through different metals.

If a copper rod was used, you probably foundits toothpicks fell off first.

All metals are good heat conductors, but copper is really excellent.

Two (or more) different-metal rods, held byclamps, heated at one end by a bunsen.

Toothpicksstuck on with

grease or wax.

As heat conductsthrough the

metals, the waxmelts and the

toothpicks drop off.

Heat Conduction in the Kitchen

Look at the features of a typical saucepan,and relate them to the conduction of heatenergy.

Copper bottom forrapid heat conduction

from the stove

The body is made ofstainless steel forstrength, hygiene,easy cleaning andnice appearance.

To avoid being burned, the parts that a person needs to touch are

made of insulating plastic.

Investigating ConvectionYou may have done an experiment similarto this:

The coloured dye makes any movement ofthe water visible.

The hotter water (directly above the bunsen) flows upwards, then spreadsacross the top, then sinks down the sidesto complete a circuit.

This is a convection current, which movesheat quickly through gases (e.g. theatmosphere) and liquids (e.g. oceans).

Beaker of water.

One drop of coloured

food dye so water

currents are visible.

Watch closely, it only

works for a short

time.

Tripod & Gauze.

Bunsen.

convectioncurrents in

water.

Investigating RadiationTwo identical cans, one painted black, theother white/silver. Thermometers measure

the temperature inside.

If placed in sunshine (orradiation from an electric

radiator) you will find:

• the black can heatsup faster because it

absorbs heat radiation.

• the white/silver canheats more slowlybecause it reflects

radiation.

Don’t forget, heat radiation is a type of

wave called “Infra-Red”.




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Electrical EnergyThe most useful form of energy for oursociety is electricity. It is so usefulbecause:

• electricity can be produced in one place(e.g. in a power station) and movedinstantly to wherever the energy is needed.

• electricity can be easily converted intomany other forms of energy, as needed.e.g. it is easily converted to heat, light, etc.

What is Electricity?

Electricity is a flow of tiny particles calledelectrons. Electrons can flow through somesubstances (electrical conductors), but notthrough other things (electrical insulators).

Electrical Conductors InsulatorsAll Metals, Plastics, cotton,(Copper is wood, air,especially good) pure water.graphite, salty water.

Notice that generally (but there are a fewexceptions) the things that are good heatconductors are also good electrical conductors.

Generally, heat insulators are also electrical insulators.This familiar item can convert electricity

into light and into K.E.

Electrical Conductor or Insulator?This equipment set-up is suitable totest the electrical conductivity of avariety of objects or substances.

The alligator clips are attached to thetest object, then the power

is turned on.

If the bulb lights up, it means that electricity is flowing through the entire

circuit. Therefore, the test object is a conductor.

If the bulb does not light, then electricity is not getting through. Therefore, the test object is not a conductor... it is an insulator.

ACoff

on

DC

PowerPack

LightBulb

Wires with alligator

clips

Substance to be tested for conductivity

- +




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Electrical Circuits

Electricity is a flow of tiny particles calledelectrons. They can flow through a wire (or other conductor) by rapidly “jumping”from atom to atom. However, they cannotjump onto the atoms of an insulating material. This why an insulator can blockelectricity and stop it getting through.

Each electron carries some negativeelectric charge.

For electricity to flow at all, there must bea complete circuit (i.e. an unbroken chainof conductors) from the negative (-) terminal to the positive (+) terminal.

It turns out that there are two kinds of electric charge, with opposite properties. We could have called them “black” & “white”, or “left” &

“right”, but they ended up being called “positive” & “negative”.

ACoff

on

DC

- +

Electrons come from the negative terminal and flowaround the circuit to the +ve terminal.

Electrical Voltage & Current Voltage Makes the Electrons FlowThe amount of electrical energy carried by each electronis determined by the voltage of the power source. Thehigher the voltage, the bigger the “push” given to eachelectron. The unit of measurement is the “volt” (V).

Small electrical batteries provide 1.5V, (safe to handle)and your school power pack can give up to 12V (fairlysafe). Mains electricity is 240V (deadly dangerous) and power distribution lines may be 100,000Vor more. (don’t go there!)

Electrical CurrentElectrical current is a measure of how many electrons are flowing. Current is measured in unitscalled “amperes” (abbreviated to “amps”) (A). 1 A of current involves the flow of many billions ofelectrons per second.

Energy Conversion in an Electrical CircuitSince voltage determines how much energy each electron has, and current measures how manyelectrons flow, then the total energy of a circuit depends on both voltage and current.

The energy produced (per sec.) by a circuit is called “Power”, and is measured in “watts” (W). If you look at the labels on electrical devices it will tell you their power rating in watts or kilowatts(kW). For example, if an appliance is rated as “1kW” this means it uses 1,000 units of energy persecond.

If there is any break in the circuit (e.g. a wire not connected properly) the electrons cannot get through and the whole circuit stops working.

Please complete Worksheets 8 & 9before going on.




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Conservation of EnergyThe word “conservation” simply means to keep things the same.

When applied to energy it refers to the fact that, whenever a change occursand energy is transformed into another type, the total amount of energyafter the change is exactly the same amount as there was before thechange.

You cannot get energy from nothing... it cannot be created. You always getenergy from something that has energy in it, often stored as Potential

Energy (PE). When you use energy, it doesn’t just “disappear” and cease toexist.... it transforms into other types of energy, but it is never destroyed.

For example, in this simple circuit, electricityis being converted into light and heat energy.

If you measure the amount of electrical energy being used, and the amount of lightand heat energy being produced, the total isthe same.

Amount of Electrical = Amount of Light & Heat Energy used Energy Produced

This concept is one of the most important basic principles of Science. It isoften expressed in this way:

“Energy cannot be created, nor destroyed. When energy is transformed, the total energy before

is equal to the total energy after the change.”

This is called the “LAW OF CONSERVATION OF ENERGY”

ACoff

on

DC

- +

Please complete Worksheet 10 before going on.




Efficient Energy UseWhen we use energy it is converted into different types of energy.

However, not all of it converts into the type of energy we might want.

For example, when we burn petrolto power a car, what we really wantis for the energy to convert to KE tomake the car move. (Plus a little electricity for the lights, radio, etc)

In reality, only about 10% ofthe energy originally in thepetrol ends up as KE.

90% is “wasted” as (mainly)heat energy, which spreadsout into the surroundings and is no longer useful.

A car is only about 10% efficient in energy!

Old-style light bulbs are also veryinefficient. They are designed toconvert electricity into light energy,but over 80% of the energy used isconverted into heat instead of light.

These bulbs are now beingphased out and soon theywill no longer be available.

The old light bulbs are being replaced by“compact fluorescent tubes” (pictured) orby L.E.D. lights which are much more efficient. For example, the 2 bulbs pictured can produce the same amount oflight, but the compact fluoro light uses

only about 1/5 as much electricity.

Sometimes when people talkabout energy efficiency theyare not referring to the actualconversion of energy, but to

unecessary wastage of energy.

For example, an electric room heater might be quite efficient at converting electricity into heat energy, but ifthe room is poorly insulated and the windows left open,then the heat escapes and is lost. To keep the room warm,you have to run the heater on “high” constantly and useextra electricity unecessarily. This is another way to thinkabout efficiency.

Another Meaning for “Efficient Use of Energy”

What are the benefits of efficient energy conversions and usage?

Power CostsThe average Australian household usesabout 6,500 units of electricity per year. At 2012 prices, this costs around $2,000.

By using energy-efficient lights and appliances, insulating homes (or at leastclosing windows when the heater or air-con is going) and turning things offwhen not in use, it is not difficult toreduce consumption by 10-20%. Yes, itcosts extra to buy different lights, or insulation, but in the long-term you willsave money.

Energy used in homes is only about 8% ofour total national usage. Huge amounts ofelectricity are used for street lights,offices and businesses. The same ideasapply... energy-efficient lights, insulationand avoiding wastage can save hugesums of money in the long run.

Less EmissionsOver 90% of Australia’s electricity ismade from fossil fuels, mostly from burning coal.

The average household uses 6,500 unitsof electricity per year. To generate thiselectricity, almost 6,000 kg of CO2 gas is

released into the air and contributes tothe environmental problems.

If every household reduced electricityusage by 20%, this would reduce emissions by about 5 million tonnes ofCO2 across the whole nation.

Don’t forget that domestic power use isonly a small fraction of that used in businesses, factories and public places,so greater efficiency there could reduceemissions by even greater amounts.

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In a previous topic you studied Simple Machines and Forces.Now we take another look and connect Forces to Energy.

Putting Forces to WorkThere are many situations when weneed to move or lift things usingforce. Often it makes the task fasteror easier if we use some kind ofmachine.

Simple MachinesA simple machine is a device whichchanges forces to our advantage.

Simple machines include Levers, Gears & Pulleys.

In a later topic you will study more about simplemachines. For now, we will only cover some basicideas. An interesting activity is outlined next page.

LeversA lever is perhaps the simplest of all simplemachines.

In this photo, a claw hammer is being used to pull outa bent nail. You could NOT do this easily with your fingers because the force required is too great. Usingthe hammer as a lever gives you a force advantagewhich easily pulls the nail.

Some simple machines make things go faster,such as a bicycle chain system.

The sprocket on the rear wheelaxle is smaller then the one atthe pedals. This causes therear wheel to rotate fasterthan the pedals, so yougain an advantage inspeed.

Similarly, the gear box of a car containstoothed wheels which “mesh” with each otherto change the speed of rotation of thewheels comparedto the engine.

In high gear, thecar goes fasterbecause it gets aspeed advantage.In low gear, it goes slower, but can tow heavyloads or climb steep hills because the gearsgive a force advantage.

Please do the activity outlined on the next page, then come back to the section below.

Forces, Machines & WorkIn everyday language, “work” means to do useful things for money.

However, in Physics “work” has a specific meaning to do with forces.

Work Done by a ForceThe Physics definition of “work” is:

Work = Force x Distance

The distance involved is the distance over whichthe force acts. At this stage we will ignore the unitsof measurement. (KISS Principle)

Analysing the Pulley ResultsWith a knowledge of “work”, now you can analyseyour results of the pulley investigation (next page).Calculate as follows for each set of measurements:a)

Work Output = Load X distance that loadfrom the machine Force was moved

b)Work Input = Effort X distance that the

into the machine Force effort moved

The Work Output can never be greaterthan the Work Input.

Output can be less than input, because some workgets used up with friction. In a perfect machine, output and input would be equal. However, it is abasic rule of Physics that output can NEVER begreater than input.

Work & Simple MachinesWhen a simple machine gives you a force advantage, it sounds a bit like getting something fornothing. However, in terms of Work Input and Outputthis is NOT true.

Larger distance

moved by the effort

Smalldistance

moved bythe load

The diagrams show a person liftinga heavy box with a lever. The lever

gives a force advantage,but look at the distances.

EffortForce

Fulcrum (pivot point)

Load

Force

When you analyse the Work Input & Output youalways find that you have NOT got something fornothing... the Output will always be less than the

Input. There’s no such thing as a free lunch!

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Investigating Pulley SystemsHere is an outline of a simple way to investigate the idea of the “force advantage” which some simple machines can give you.

Str

ing

Fixedsupport

Bench

Pulley wheel

Spring balancemarked in newtons

Readspring

balancewhile lifting

slowly andsteadily

250g slottedmasses

Step 1

Step 2

Weigh the combined pulley wheel and slotted masses in newtons (N).This is the “Load” that you will lift. It will be about 3N.This weight is the force (due to gravity) that you must overcome to lift the load.

Note: Pulleys are usually arranged so that you pull down to liftthe load. We are arranging it so you lift upwards, because the

spring balance will not work accurately if upside down.

You will find that the“Effort Distance” and“Load Distance” are

NOT equal.Can you find a pattern

between these distances and the difference in the

forces?

Set up equipment as shown, below left.

Measure the “Effort force” needed to liftthe load by lifting with the spring balance.

Weightsjust

touchingbench to

start

Hold stringwith fingersto measure

the lift distances.

This is the “LoadDistance” that the

weights move.

Str

ing

Fixedsupport

Me

tre

ru

le

Now measurethe distancesmoved by theeffort & load

forces.

Bench

Step 3T

his

dis

tan

ce

is

th

e“E

ffo

rt D

ista

nc

e”

wh

ich

yo

ur

fin

gers

mo

ve

to

lif

t th

e l

oad

.

Step 2

If the “effort force”is less than the

“load force” beinglifted, it means thepulley is giving youa force advantage.

It is making the lifting job easier.

You might repeat the entire experiment several times,using a different amount of “Load” each time.

Record all your measurements

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Work & EnergyWhen it comes to the work done by a simple machine,

you CANNOT get something for nothing. Hang on, we’ve heard that before...

Work = EnergyNo wonder it sounds familiar!

Work IS energy and (remember!) energy must be “conserved”. The workyou get out of a machine cannot be more than the work put in,

else it would mean extra energy for nothing.

Of course, you can get less work out of a machine than what you put in.Friction might rob you of some energy by converting it to useless low-grade

heat which then dissipates into the environment. The energy still exists (so energy is conserved) but is now useless and cannot do “work”.

No machine (or any energy converting device) is 100% efficient. Some energy is always “lost” due to friction, or electrical resistance, etc.

Further Experimental InvestigationsYou may be able to carry out more experiments with pulleys to investigate this further.

Previous Activity Further set-ups to try

Finally, calculate as follows:%Efficiency = Work Output on Load x 100

Work Input by Effort

Load

Fixedsupport

SinglePulley

2 SinglePulleys

DoublePulley

Effort

SinglePulley

2DoublePulleys

If you do the activities shown below, your results should show:

• You NEVER get more energy out than what was put in. (Work Output is equal to, or LESS than, Work Input)

This is consistent with The Law of Conservation of Energy.

• As the machine gets more complex (or carries a heavier load) there ismore friction and lower efficiency. (If not noticeable, try it again with a heavier load)

For each pulley system youshould measure “load force”and “effort force”. Look for a

pattern in the “force advantage” which each

system gives.

You should also measure thedistances moved by load andeffort forces, then calculate

the “work input” by the effortforce and the “work output”

done on the load.

(WORK = FORCE x distance)

Please complete Worksheet 11after this page.

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