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Work and Simple Work and Simple MachinesMachines

WorkWorkAnswer the following questions with your elbow partner.Answer the following questions with your elbow partner.

What is work?What is work? Does everyone do work?Does everyone do work?

We are going to contrast situations where We are going to contrast situations where work is done with different amounts of force to work is done with different amounts of force to situations were no work is donesituations were no work is done

For example:For example: Moving a box with and without a rampMoving a box with and without a ramp Standing still Standing still

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What is work?What is work?

In science, the word In science, the word work has a has a different meaning than you may be different meaning than you may be familiar with.familiar with.

The scientific definition of work is: The scientific definition of work is: using ausing a force to move an object a force to move an object a distancedistance Both the Both the forceforce and the and the motionmotion of the of the

object are object are in the same directionin the same direction.. Examples: Examples: pushing, pulling or liftingpushing, pulling or lifting

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Work or Not?Work or Not?

According to the According to the scientific definition, scientific definition, what is work and what is work and what is not?what is not? a teacher lecturing a teacher lecturing

to her classto her class a mouse pushing a a mouse pushing a

piece of cheese piece of cheese with its nose across with its nose across the floorthe floor

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Work or Not?Work or Not?

According to the scientific definition, what is work and what is not?

a teacher lecturing to her class

a mouse pushing a piece of cheese with its nose across the floor

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What’s work?What’s work?Elbow partner timeElbow partner time

1.1. A scientist delivers a speech to an A scientist delivers a speech to an audience of his peers. audience of his peers.

2.2. A body builder lifts 350 pounds A body builder lifts 350 pounds above his head. above his head.

3.3. A mother carries her baby from A mother carries her baby from room to room.room to room.

4.4. A father pushes a baby in a A father pushes a baby in a carriage.carriage.

5.5. A girl pushes on a wall during PE.A girl pushes on a wall during PE.

What’s work?What’s work?1.1. A scientist A scientist delivers a speech to an audience of his delivers a speech to an audience of his

peers. peers. NoNo

2.2. A body builder lifts 350 pounds above his head. A body builder lifts 350 pounds above his head. YesYes

3.3. A mother carries her baby from room to room. A mother carries her baby from room to room. NoNo

4.4. A father pushes a baby in a carriage. A father pushes a baby in a carriage. YesYes

5.5. A woman pushes on a wall during PE.A woman pushes on a wall during PE. NoNo

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Formula for workFormula for work

Work = Force x DistanceWork = Force x Distance

The unit of The unit of forceforce is is newtons (N)newtons (N) The unit of The unit of distancedistance is is meters (m)meters (m) The unit of The unit of workwork is is newton-meters (Nm)newton-meters (Nm) One newton-meterOne newton-meter is is equalequal to to one joule one joule So, the unit of So, the unit of workwork is a is a joule (J)joule (J)

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W=FDW=FD

Work = Force x Work = Force x DistanceDistance

Calculate: If a man Calculate: If a man pushes a pushes a concrete block 10 concrete block 10 meters with a meters with a force of 20 N, force of 20 N, how much work how much work has he done?has he done?

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W=FDW=FD

Work = Force x Work = Force x DistanceDistance

Calculate: If a man Calculate: If a man pushes a concrete pushes a concrete block 10 meters block 10 meters with a force of 20 N, with a force of 20 N, how much work has how much work has he done? he done? 200 joules200 joules(W = 20N x 10m)(W = 20N x 10m)

White board practice timeWhite board practice time

WorkWorkExample # 1Example # 1

What work is done to What work is done to move a crate if the force move a crate if the force applied is 345 N and the applied is 345 N and the crate is moved 6 m?crate is moved 6 m?

W=FxDW=FxD 345 N,345 N, 6 M6 M

W = ?W = ?W = 345 N x ?W = 345 N x ?W = 345 N x 6 MW = 345 N x 6 MW = 2070 JW = 2070 J

WorkWorkExample # 2Example # 2

A fork lift moves 30m A fork lift moves 30m carrying a 1023N box carrying a 1023N box across the warehouse across the warehouse floor. How much work is floor. How much work is done by the fork lift.?done by the fork lift.?

W=F X D W=F X D 1023 N, 30 m1023 N, 30 m

W=FxDW=FxDW = ?W = ?W= 1023 N x ?W= 1023 N x ?W = 1023 N x 30 mW = 1023 N x 30 mW = 30690 JW = 30690 J

WorkWorkExample # 3Example # 3

How much work is done by a How much work is done by a person who uses a force of person who uses a force of 27 N to move a grocery 27 N to move a grocery buggy 12 m?buggy 12 m?

W=FxDW=FxD 27 N,27 N, 12m12m

W= FxDW= FxDW = 27 N x ?W = 27 N x ?W = 27 N x 12 mW = 27 N x 12 mW= 324 NmW= 324 NmW = 324 JW = 324 J

Example # 4Example # 4

How much work is done to lift a How much work is done to lift a weight that has a mass of 75 N to weight that has a mass of 75 N to a height of 2 m? a height of 2 m?

W = F x DW = F x D 75 N,75 N, 2 m2 m

W = F x DW = F x D W = 75 N x ?W = 75 N x ? W = 75 N x 2 mW = 75 N x 2 m W = 150 JW = 150 J

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History of WorkHistory of Work

Before engines and motors were invented, people Before engines and motors were invented, people had to do things like lifting or pushing heavy loads had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they by hand. Using an animal could help, but what they really needed were some clever ways to either really needed were some clever ways to either make work easier or faster. make work easier or faster.

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Simple MachinesSimple Machines

Ancient people invented simple machines Ancient people invented simple machines that would help them overcome resistive that would help them overcome resistive forces and allow them to do the desired forces and allow them to do the desired work against those forces. work against those forces.

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Simple MachinesSimple Machines

Inclined Plane Inclined Plane Pulley Pulley Lever Lever Wheel and Axle Wheel and Axle Wedge Wedge Screw Screw

Can you name the 6 simple machines from memory?

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Simple MachinesSimple Machines

A machine is a device that A machine is a device that helps helps make work easier make work easier by changing: by changing: the amount of force you exertthe amount of force you exert the distance over which you exert your the distance over which you exert your

forceforce The direction in which you exert your The direction in which you exert your

forceforce

Contrasting WorkContrasting Work

You lift a 10 Newton box onto a moving You lift a 10 Newton box onto a moving truck that is 1.5 meters high. How much truck that is 1.5 meters high. How much work did you do?work did you do?

W= FxDW= FxD W= 10 N x 1.5 mW= 10 N x 1.5 m W= 15 Joules W= 15 Joules

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Contrasting WorkContrasting Work

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It takes 5 Newtons of force to push the It takes 5 Newtons of force to push the same box onto a moving truck using a same box onto a moving truck using a ramp that is 3 meters long. How much ramp that is 3 meters long. How much work did you do? work did you do? (assume there is no friction on the ramp)(assume there is no friction on the ramp)

W= FxDW= FxD W= 5 N x 3 mW= 5 N x 3 m W= 15 Joules W= 15 Joules The The same amount of work same amount of work is done is done

but the ramp makes the work easier.but the ramp makes the work easier.

Contrasting WorkContrasting Work

You are leaning on one of the boxes you You are leaning on one of the boxes you need to move with a force of 20 Newtons need to move with a force of 20 Newtons but the box doesn’t move. How much but the box doesn’t move. How much work is done?work is done?

W=FxDW=FxD W= 20 N x 0 mW= 20 N x 0 m W= 0 joulesW= 0 joules No work done on the boxNo work done on the box

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