Post on 03-Jan-2016
Mr KueresMr Kueres
Pressure and MomentsPressure and Moments
Lesson 1: Force and PressureLesson 1: Force and Pressure
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Lesson ObjectivesLesson Objectives
1.1. To know what a force does and about To know what a force does and about balanced and unbalanced forces – balanced and unbalanced forces – especially air resistance and friction especially air resistance and friction
2.2. To know that pressure depends on the To know that pressure depends on the size of a force and the area over which it size of a force and the area over which it is exertedis exerted
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What is a Force?What is a Force?
What Can a Force Do?What Can a Force Do?
A force can change the:A force can change the:
SizeSize
ShapeShape
SpeedSpeed
And Direction of an objectAnd Direction of an object
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Balanced ForcesBalanced Forces
If the forces on an object are balanced, they will have If the forces on an object are balanced, they will have no effect on the motion of an object.no effect on the motion of an object.
I.e. The person (opposite) will remain stillI.e. The person (opposite) will remain stillOr a car moving at 30mph with balanced forces acting on Or a car moving at 30mph with balanced forces acting on
it, will continue to travel at 30mphit, will continue to travel at 30mph
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Unbalanced ForcesUnbalanced ForcesIfIf the forces on an object are the forces on an object are unbalancedunbalanced, they will , they will
have some have some effecteffect on the object’s motion (either on the object’s motion (either change the change the directiondirection or cause the object to or cause the object to speedspeed up or up or slowslow down. down.
Will the car below speed up or slow down?Will the car below speed up or slow down?
Thrust (driving force)
Drag (Resistive forces)
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PressurePressure
Pressure tells us about the effect of a force Pressure tells us about the effect of a force compared with the area over which it acts.compared with the area over which it acts.
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Things to DoThings to DoAnswer the questions on the worksheet ‘Big Pressure, Small Pressure’ – Answer the questions on the worksheet ‘Big Pressure, Small Pressure’ – 10 minutes10 minutes(H) Draw a table, as shown below, illustrating examples of large area/low (H) Draw a table, as shown below, illustrating examples of large area/low pressure and small area/high pressurepressure and small area/high pressure(F) Draw examples of things that will exert a high pressure because of its (F) Draw examples of things that will exert a high pressure because of its small surface area and a low pressure because of its large surface area.small surface area and a low pressure because of its large surface area.
Large Area/Low Large Area/Low PressurePressure
Small Area/High Small Area/High PressurePressure
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HomeworkHomework
Complete Worksheet ‘But Why?’Complete Worksheet ‘But Why?’
DUE IN: Next lessonDUE IN: Next lesson
If you have any questions about the If you have any questions about the homework, come and see me before it is homework, come and see me before it is due in.due in.
Mr KueresMr Kueres
Pressure and MomentsPressure and Moments
Lesson 2: Calculating Lesson 2: Calculating PressurePressure
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Lesson ObjectivesLesson Objectives
1.1. To recall and use the formula for To recall and use the formula for pressurepressure
2.2. To know the units for pressure, force and To know the units for pressure, force and areaarea
3.3. To be able to estimate area reliablyTo be able to estimate area reliably
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PressurePressure
Pressure is dependent on fPressure is dependent on f and and
aa ..
If the fIf the f applied gets larger, the p applied gets larger, the p will be will be hh ..
If the aIf the a becomes larger, the pressure will be becomes larger, the pressure will be ss ..
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PressurePressure
Pressure is dependent on Pressure is dependent on forceforce and and
areaarea..
If the If the forceforce applied gets larger, the applied gets larger, the pressurepressure will be will be higherhigher..
If the If the areaarea becomes larger, the pressure will becomes larger, the pressure will be be smallersmaller..
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Formula for PressureFormula for Pressure
PressurePressure == ForceForce
AreaArea
Force is measured in N , N.Area is measured in s m , m2.Pressure is measured in Newtons per square metre, N/m2 or P , Pa.
PP == FF
AA
Mr KueresMr Kueres
Formula for PressureFormula for Pressure
PressurePressure == ForceForce
AreaArea
Force is measured in Newtons, N.Area is measured in square metres, m2.Pressure is measured in Newtons per square metre, N/m2 or Pascals, Pa.
PP == FF
AA
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Finding the Pressure we Exert Finding the Pressure we Exert on the Flooron the Floor
APPARATUSAPPARATUScm Squared Papercm Squared PaperBathroom ScalesBathroom Scales
METHODMETHOD
Draw around your foot on the piece of squared paper.Draw around your foot on the piece of squared paper.Count the squares and estimate the area of your foot Count the squares and estimate the area of your foot (More than half a square counts as 1, less than half a (More than half a square counts as 1, less than half a square doesn’t count).square doesn’t count).Use the bathroom scales to find your body WEIGHT. Use the bathroom scales to find your body WEIGHT. Remember: weight is a force and measured in Remember: weight is a force and measured in NEWTONS) (1kg ~ 10N).NEWTONS) (1kg ~ 10N).Calculate the pressure exerted by each foot, then both Calculate the pressure exerted by each foot, then both feet together.feet together.
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Calculation for One FootCalculation for One Foot
Pressure exerted by one footPressure exerted by one foot == Half body weightHalf body weight
Area of footArea of foot
==
== N/cmN/cm22
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Calculation for Both FeetCalculation for Both Feet
Pressure exerted by one footPressure exerted by one foot == Body weightBody weight
2 x Area of foot2 x Area of foot
==
== N/cmN/cm22
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EvaluationEvaluation
Give one reason why you think your Give one reason why you think your experiment was accurate and one reason experiment was accurate and one reason why you think your experiment was not why you think your experiment was not very reliable very reliable
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Things to DoThings to Do
(H) Answer the questions on the Pressure (H) Answer the questions on the Pressure Practice Worksheet in your exercise Practice Worksheet in your exercise books.books.
(F) Complete the worksheet 9La/3: Pressure (F) Complete the worksheet 9La/3: Pressure PointsPoints
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Pressure and MomentsPressure and Moments
Lesson 3: Compression of Lesson 3: Compression of Liquids and Gases Liquids and Gases
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Lesson ObjectivesLesson Objectives
1.1. To review the formula for pressureTo review the formula for pressure
2.2. To know whether liquids and gases can To know whether liquids and gases can be compressedbe compressed
3.3. To know that liquids transmit pressureTo know that liquids transmit pressure
4.4. To know that pressure increases with To know that pressure increases with fluid depthfluid depth
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Pressure FormulaPressure Formula
As the force increases, pressure increases.As the force increases, pressure increases.
If the surface area increases, pressure will If the surface area increases, pressure will decrease.decrease.
PressurePressure ==ForceForce
AreaAreaPP == FF
AA
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PressurePressure
= force/area. There is a direct relationship = force/area. There is a direct relationship between pressure and force – increasing the force between pressure and force – increasing the force
the pressure (provided that the area stays the pressure (provided that the area stays the same). There is an the same). There is an relationship relationship between force and area – increasing the area decreases between force and area – increasing the area decreases the pressure (provided that the pressure (provided that stays stays the same). If force is measured in the same). If force is measured in
, N, and area is measured in , N, and area is measured in metres, m2, then the unit of pressure is the metres, m2, then the unit of pressure is the
..The atmosphere exerts pressure. Outside the Earth’s The atmosphere exerts pressure. Outside the Earth’s
, there is no air and no , there is no air and no atmospheric pressure. Water also exerts pressure. atmospheric pressure. Water also exerts pressure. Water exerts more pressure at greater Water exerts more pressure at greater
..
Mr KueresMr Kueres
PressurePressure
PressurePressure = force/area. There is a direct relationship = force/area. There is a direct relationship between pressure and force – increasing the force between pressure and force – increasing the force increasesincreases the pressure (provided that the area stays the the pressure (provided that the area stays the same). There is an same). There is an inverseinverse relationship between relationship between pressure and area – increasing the area decreases the pressure and area – increasing the area decreases the pressure (provided that pressure (provided that forceforce stays the same). If force is stays the same). If force is measured in measured in NewtonsNewtons, N, and area is measured in , N, and area is measured in squaresquare metres, m metres, m22, then the unit of pressure is the , then the unit of pressure is the PascalPascal..
The atmosphere exerts pressure. Outside the Earth’s The atmosphere exerts pressure. Outside the Earth’s atmosphereatmosphere, there is no air and no atmospheric pressure. , there is no air and no atmospheric pressure.
Water also exerts pressure. Water exerts more pressure Water also exerts pressure. Water exerts more pressure at greater at greater depthdepth..
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Compression in Liquids and GasesCompression in Liquids and Gases
In a gas, the In a gas, the are a long way are a long way
apart and it’s not too hard apart and it’s not too hard to push them closer to push them closer
..In a In a , it’s , it’s
very hard to very hard to particles much closer particles much closer together.together.
So, the particle model can So, the particle model can explain the different explain the different
of of gases and liquids under gases and liquids under
..
Gas
Gas
Gas
Gas
Mr KueresMr Kueres
Compression in Liquids and GasesCompression in Liquids and Gases
In a gas, the In a gas, the particlesparticles are a are a long way apart and it’s not long way apart and it’s not too hard to push them too hard to push them closer closer togethertogether..
In a In a liquidliquid, it’s very hard to , it’s very hard to pushpush particles much particles much closer together.closer together.
So, the particle model can So, the particle model can explain the different explain the different
behaviourbehaviour of gases and of gases and liquids under liquids under
pressurepressure..
Gas
Gas
Gas
Gas
Mr KueresMr Kueres
Introduction to HydraulicsIntroduction to Hydraulics
Many robots use hydraulics or Many robots use hydraulics or liquid pressure. There are two liquid pressure. There are two cylinders – a master cylinder cylinders – a master cylinder and a slave cylinder – and a slave cylinder – connected by a sturdy pipe. connected by a sturdy pipe. The master cylinder contains The master cylinder contains the effort piston and the slave the effort piston and the slave cylinder contains the load cylinder contains the load piston. The slave does piston. The slave does everything that its master tells it everything that its master tells it to do, but it does it with more to do, but it does it with more force than the master could force than the master could manage. Hydraulics are also manage. Hydraulics are also used in jacks to lift up cars.used in jacks to lift up cars.
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Effort
XNon-Return Valve
Small piston provides the effort but moves along way
Large piston lifts the load but doesn’t move as far
Hydraulic fluid is pushed through
Increased pressure results in load being lifted
The Hydraulic JackThe Hydraulic Jack
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HydraulicsHydraulics
If the load piston has an area 5 times that of If the load piston has an area 5 times that of the effort piston, the load lifted is 5 times the effort piston, the load lifted is 5 times the effort, BUT moves only 1/5 the the effort, BUT moves only 1/5 the distance.distance.
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QuestionsQuestions
1.1. Why do we use oil and not water in Why do we use oil and not water in hydraulic machines? hydraulic machines?
2.2. What is the non-return valve for? What is the non-return valve for?
3.3. What would happen if there was an air What would happen if there was an air bubble in the pipe work between two bubble in the pipe work between two cylinders? cylinders?
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Motor Vehicle BrakesMotor Vehicle Brakes
If liquids are useful because they are If liquids are useful because they are incompressible and air in hydraulic fluid incompressible and air in hydraulic fluid prevents it working effectively, why do prevents it working effectively, why do some vehicles have brakes operated by some vehicles have brakes operated by compressed air?compressed air?
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Hydraulics ReviewHydraulics Review
A A system can convert a small force into system can convert a small force into a bigger force. The system is filled with liquid, which is a bigger force. The system is filled with liquid, which is
..The force acting on the piston in the master cylinder acts The force acting on the piston in the master cylinder acts
over a small over a small . The . The is is transmitted through the liquid, so the same pressure acts transmitted through the liquid, so the same pressure acts on the piston in the slave cylinder, but it acts over a bigger on the piston in the slave cylinder, but it acts over a bigger area. The same pressure acting over a bigger area area. The same pressure acting over a bigger area produces a bigger produces a bigger ..
A gas is of no use in a hydraulic system because it is A gas is of no use in a hydraulic system because it is . Pressure acting on a gas pushes the . Pressure acting on a gas pushes the
closer together. In a closer together. In a the particles are already close together and it’s the particles are already close together and it’s
very hard to make them closer.very hard to make them closer.
Mr KueresMr Kueres
Hydraulics ReviewHydraulics Review
A A hydraulichydraulic system can convert a small force into a bigger system can convert a small force into a bigger force. The system is filled with liquid, which is force. The system is filled with liquid, which is
incompressibleincompressible..The force acting on the piston in the master cylinder acts The force acting on the piston in the master cylinder acts
over a small over a small areaarea. The . The pressurepressure is transmitted through is transmitted through the liquid, so the same pressure acts on the piston in the the liquid, so the same pressure acts on the piston in the slave cylinder, but it acts over a bigger area. The same slave cylinder, but it acts over a bigger area. The same pressure acting over a bigger area produces a bigger pressure acting over a bigger area produces a bigger forceforce..
A gas is of no use in a hydraulic system because it is A gas is of no use in a hydraulic system because it is compressiblecompressible. Pressure acting on a gas pushes the . Pressure acting on a gas pushes the particlesparticles closer together. In a closer together. In a liquidliquid the particles are the particles are
already close together and it’s very hard to make them already close together and it’s very hard to make them closer.closer.
Mr KueresMr Kueres
Deep Sea DivingDeep Sea DivingWhy does a diver need to breathe compressed air?Why does a diver need to breathe compressed air?
The pressure of the water above him makes it hard to inhale with out the gas helping.
The pressure is due to the mass of water above him.
Pressure = Weight of water Area of diver
The pressure exerted depends on:
1. the depth2. the weight of the fluid
(hence, its density)
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Dep
th o
f w
ater
in m
etre
s
Wat
er p
ress
ure
in k
ilopa
scal
s
10
20
30
40
50
100
200
300
400
500
Mr KueresMr Kueres
Submarine PressureSubmarine Pressure
Depth of water in metres
Water pressure in kilopascals
1010 100100
2020 200200
3030 300300
4040 400400
5050 500500
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Things to DoThings to Do
Answer the Questions on the Submarine Answer the Questions on the Submarine Pressure worksheetPressure worksheet
Answer the Questions on the Water Answer the Questions on the Water Pressure worksheetPressure worksheet
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Submarine PressureSubmarine Pressure
The bigger the depth of water, the The bigger the depth of water, the bb the water pressure is. For example, the water pressure is. For example,
if the depth doubles then water pressure if the depth doubles then water pressure also also dd . And if the depth . And if the depth trebles then trebles then ww pp trebles. In trebles. In fact, whenever the depth changes, the fact, whenever the depth changes, the water pressure always changes by the water pressure always changes by the same same pp ..
Mr KueresMr Kueres
Submarine PressureSubmarine Pressure
The bigger the depth of water, the The bigger the depth of water, the biggerbigger the the water pressure is. For example, if the water pressure is. For example, if the depth doubles then water pressure also depth doubles then water pressure also doublesdoubles . And if the depth trebles then . And if the depth trebles then waterwater pressurepressure trebles. In fact, whenever trebles. In fact, whenever the depth changes, the water pressure the depth changes, the water pressure always changes by the same always changes by the same proportionproportion..
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Pressure & MomentsPressure & Moments
Lesson 4: MomentsLesson 4: Moments
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Lesson ObjectivesLesson Objectives
1.1. To know that a force can produce a turning To know that a force can produce a turning effecteffect
2.2. To know that the turning effect is called a To know that the turning effect is called a momentmoment
3.3. To know that the moment of a force depends To know that the moment of a force depends on the size of the force and the distance of the on the size of the force and the distance of the force from the pivotforce from the pivot
4.4. To know that the pivot is also called a FulcrumTo know that the pivot is also called a Fulcrum
5.5. To be able to calculate the moment of a forceTo be able to calculate the moment of a force
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Turning EffectsTurning Effects
Write a list of examples of where a force Write a list of examples of where a force produces a turning effect.produces a turning effect.
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DemonstrationDemonstration
Try opening a door in each of these three Try opening a door in each of these three places:places:
1.1. A point furthest away from the hingesA point furthest away from the hinges
2.2. A point roughly in the centre of the doorA point roughly in the centre of the door
3.3. A point close to the hingesA point close to the hinges
At which point is it the most difficult to open At which point is it the most difficult to open the door?the door?
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DemonstrationDemonstration
Hold a metre ruler horizontally at arms length. If we apply a Hold a metre ruler horizontally at arms length. If we apply a 10N weight near your hand, then gradually move the 10N weight near your hand, then gradually move the weight along the ruler, what happens?weight along the ruler, what happens?
We find that it becomes increasingly difficult to hold the ruler horizontal.
This is because the mass exerts a turning effect on the ruler.
The turning effect is called a MOMENT and depends on the weight and the distance from the pivot
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MomentsMoments
The turning effect caused by a force is The turning effect caused by a force is called a called a momentmoment and depends on the and depends on the forceforce ( (weightweight) applied and the ) applied and the distancedistance from the pivot.from the pivot.
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MomentsMoments
Moment = Force Exerted x Distance from the PivotMoment = Force Exerted x Distance from the Pivot
Moment = F x dMoment = F x d
UNITSForce is measured in N , N.Distance is measured in m , m (usually c , cm, for the distances we use in class).Moments are measured in N m , Nm (or Newton centimetres if the distance is measured in that unit)
Mr KueresMr Kueres
MomentsMoments
Moment = Force Exerted x Distance from the PivotMoment = Force Exerted x Distance from the Pivot
Moment = F x dMoment = F x d
UNITSForce is measured in Newtons, N.Distance is measured in metres, m (usually centimetres, cm, for the distances we use in class).Moments are measured in Newton metres, Nm (or Newton centimetres if the distance is measured in that unit).
Mr KueresMr Kueres
Things to DoThings to Do
Complete 9Ld/3: Revision QuestionsComplete 9Ld/3: Revision Questions
Complete the Moments Example Sheet 1Complete the Moments Example Sheet 1
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Balancing ActBalancing Act
We can use the idea of moments to see why We can use the idea of moments to see why an object balances (or overbalances)an object balances (or overbalances)
G GCentre of gravity acts between the wheels – the bus is balanced
Centre of gravity acts outside of the wheels
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Things to DoThings to Do
Complete the Moments Example Sheet 2Complete the Moments Example Sheet 2
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Pressure and MomentsPressure and Moments
Lesson 5: Balancing MomentsLesson 5: Balancing Moments
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Lesson 5 - ObjectivesLesson 5 - Objectives
1.1. To know how to find whether moments To know how to find whether moments are balanced or unbalancedare balanced or unbalanced
2.2. To be able to balance simple leversTo be able to balance simple levers
3.3. To know that if a lever is balanced, the To know that if a lever is balanced, the anticlockwise and clockwise moments anticlockwise and clockwise moments are equalare equal
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Moments - ReviewMoments - Review
Moment = Force Exerted x Distance from the PivotMoment = Force Exerted x Distance from the Pivot
Moment = F x dMoment = F x d
UNITSForce is measured in Newtons, N.Distance is measured in metres, m (usually centimetres, cm, for the distances we use in class).Moments are measured in Newton metres, Nm (or Newton centimetres if the distance is measured in that unit).
Mr KueresMr Kueres
Balancing LeversBalancing LeversHow can we alter levers e.g. seesaws, so that they How can we alter levers e.g. seesaws, so that they
balance? balance? In which direction would you move the masses to make In which direction would you move the masses to make the lever above balance?the lever above balance?Could you balance the lever by moving the pivot? If so Could you balance the lever by moving the pivot? If so how?how?
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Balancing LeversBalancing LeversWe can balance the lever by:We can balance the lever by:1. Moving the light weight away from the pivot.1. Moving the light weight away from the pivot.
Lever moves clockwise
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Balancing LeversBalancing LeversWe can balance the lever by:We can balance the lever by:2. Moving the heavy weight towards the pivot.2. Moving the heavy weight towards the pivot.
Lever moves clockwise
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Balancing LeversBalancing LeversWe can balance the lever by:We can balance the lever by:3. Moving the pivot towards the heavy weight.3. Moving the pivot towards the heavy weight.
Lever moves clockwise
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Practical – Balancing LeversPractical – Balancing Levers
Use the ‘Levers’ worksheet to perform the Use the ‘Levers’ worksheet to perform the investigationinvestigation
Record your results in an appropriate tableRecord your results in an appropriate table
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ConclusionConclusion
In order for a lever to balance, the In order for a lever to balance, the
cc moment must moment must ee the the anti-clockwise anti-clockwise mm ..
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ConclusionConclusion
In order for a lever to balance, the In order for a lever to balance, the
clockwiseclockwise moment must moment must equalequal the the
anti-clockwise anti-clockwise momentmoment..
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Anti-Clockwise Moment = Clockwise Moment
Force x Distance from pivot = Force x Distance from Pivot
Total anti-clockwise moment = Total clockwise moment