April 30, April 30, 20152015

You need:You need:

Clean paper / pencilClean paper / pencil

Simple Machines foldableSimple Machines foldable

Warm Up:Warm Up:

What is your favorite simple What is your favorite simple machine? Why?machine? Why?

Work & PowerWork & Power

What is WORK?What is WORK?

If you put a lot of effort into doing If you put a lot of effort into doing something and are worn out at the something and are worn out at the end, you think you’ve done a lot of end, you think you’ve done a lot of WORKWORK, right? , right?

Not necessarily….Not necessarily…. If you haven’t exerted a force AND If you haven’t exerted a force AND

moved an object some distance, moved an object some distance, you haven’t done any WORK at all! you haven’t done any WORK at all!

What is WORK?What is WORK?

In scientific terms, you do In scientific terms, you do WORKWORK when you exert a when you exert a FORCEFORCE that that causes an object to move some causes an object to move some DISTANCEDISTANCE in the in the SAME SAME DIRECTIONDIRECTION of the force. of the force.

- Force and motion are in the SAME

DIRECTION, so work is being done.

- Force and motion are NOT in the same direction, so no work

is being done.

- Some force is in the direction of motion,

but some is not.

Calculating WORKCalculating WORK

WORK = FORCE x DISTANCEWORK = FORCE x DISTANCE

W

F D

Force = Work

Distance

Distance = Work Force

Calculating WORKCalculating WORK

You carry a baby that weighs 30 N You carry a baby that weighs 30 N upstairs to his room (3 meters above upstairs to his room (3 meters above you). How much work is done?you). How much work is done?

WORK = FORCE X DISTANCEWORK = FORCE X DISTANCE

WORK = 30 N x 3 metersWORK = 30 N x 3 meters

WORK = 90 NWORK = 90 N·m (90 J)·m (90 J)

Work is measured in Joules (J)Work is measured in Joules (J)

1 Joule = 1 1 Joule = 1 NN·m·m

What is POWER?What is POWER?

Power is the Power is the raterate at which work is at which work is being done (or how much work is being done (or how much work is being done in a unit of time).being done in a unit of time).

POWER = WORK POWER = WORK ÷ TIME÷ TIME More power means More power means less time to do less time to do

the same work the same work OR OR more work done more work done in the same amount of timein the same amount of time..

Power is measured in Watts (W).Power is measured in Watts (W).

Calculating POWERCalculating POWER

A motor exerts a force of 2,000 N to A motor exerts a force of 2,000 N to lift an elevator 8.0 m in 4.0 seconds. lift an elevator 8.0 m in 4.0 seconds. What is the power of the motor? What is the power of the motor?

Power = Power = WorkWork = = Force x DistanceForce x Distance

TimeTime Time Time

Power = Power = 2,000N x 8 m2,000N x 8 m

4 s4 s

Power = 4,000 J/s (4,000 Watts)Power = 4,000 J/s (4,000 Watts)

= = 16,000 J16,000 J

4 s4 s

Work and Power Work and Power Practice ProblemsPractice Problems

John pushes a heavy box for 4 m with a John pushes a heavy box for 4 m with a constant force of 60 N. Then Alex lifts constant force of 60 N. Then Alex lifts the box, which weighs 200 N, to a the box, which weighs 200 N, to a height of 1.5 m. Who did more work?height of 1.5 m. Who did more work?

Work = Force x Distance Work = Force x Distance

John’s Work = 60 N x 4 m = 240 joulesJohn’s Work = 60 N x 4 m = 240 joules

Alex’s Work = 200 N x 1.5 m = 300 Alex’s Work = 200 N x 1.5 m = 300 joulesjoules

Work and Power Work and Power Practice ProblemsPractice Problems

Carrie operates a forklift at the soda Carrie operates a forklift at the soda warehouse. The machine does 7,500 J warehouse. The machine does 7,500 J of work to lift a pallet of soda 3m. How of work to lift a pallet of soda 3m. How much did the soda weigh in Newtons?much did the soda weigh in Newtons?

Force = Work ÷ Distance Force = Work ÷ Distance

Force = 7500 J ÷ 3 mForce = 7500 J ÷ 3 m

Force = 2500 NForce = 2500 N W

F D

Work and Power Work and Power Practice ProblemsPractice Problems

A sled dog exerts a force of 300 N to A sled dog exerts a force of 300 N to pull the sled 400 meters in 120 pull the sled 400 meters in 120 seconds. What is the dog’s power?seconds. What is the dog’s power?

Power = Power = WorkWork = = Force x DistanceForce x Distance

TimeTime Time Time

Power = Power = 300N x 400 m300N x 400 m

120 s120 s

Power = 1,000 J/s (1,000 Watts)Power = 1,000 J/s (1,000 Watts)

= = 120,000 J120,000 J

120 s120 s

Simple Simple MachinesMachines(Making work easier…(Making work easier…phew!)phew!)

Simple Simple Machines Machines FoldableFoldable

Line up your papers Line up your papers about 1-2 cm apart, about 1-2 cm apart, so that you see “5, so that you see “5, 6, 7, 8” along the 6, 7, 8” along the bottom. bottom.

Fold the papers Fold the papers over so you see all over so you see all 8 numbers in a row.8 numbers in a row.

8 Simple Machine Notes

7 Lever

6 Pulley

5 Wheel & Axle

4 Wedge

3 Screw

2 Inclined Plane

1 Simple Machines

By John Smith

Simple Simple Machines Machines FoldableFoldable

Use your textbook Use your textbook (pg. 716-727) & (pg. 716-727) & websites to research websites to research simple machines:simple machines:

On each tab, draw On each tab, draw and describe that and describe that type of simple type of simple machine.machine.

Then give 2-3 Then give 2-3 examples.examples.8 Simple Machine

Notes

7 Lever

6 Pulley

5 Wheel & Axle

4 Wedge

3 Screw

2 Inclined Plane

Draw & Describe:

A sloped surface connecting a lower level to a higher level.Examples:

A boat ramp, wheelchair ramp,propeller, ladder/stairs

What are MACHINES?What are MACHINES?

Most people think of complex, technical, Most people think of complex, technical, or electronic gadgets with motors…, but or electronic gadgets with motors…, but machines can be much SIMPLER. machines can be much SIMPLER.

A machine is any device that lets you do A machine is any device that lets you do WORKWORK in an in an EASIEREASIER or or BETTERBETTER way. way.

Basically: Basically:

Simple machines make work Simple machines make work EASIER.EASIER.

How do machines do How do machines do work?work? Machines make work easier by Machines make work easier by

changing 3 things about the FORCE changing 3 things about the FORCE you exert to do work:you exert to do work: AMOUNTAMOUNT OF FORCE OF FORCE you exert you exert DISTANCEDISTANCE over which you exert over which you exert

forceforce DIRECTIONDIRECTION in which you exert in which you exert

forceforce

What are SIMPLE What are SIMPLE MACHINES?MACHINES?

There are only 6 basic simple There are only 6 basic simple machines that make work machines that make work easier:easier: • Inclined PlaneInclined Plane

• WedgeWedge• ScrewScrew• LeverLever• Wheel & AxleWheel & Axle• PulleyPulley

COMPOUND MACHINESCOMPOUND MACHINES

Compound Machines – are made of Compound Machines – are made of combinationscombinations of two or more of two or more simple machinessimple machines..

For example, a simple can opener is For example, a simple can opener is a combination of 3 simple machines: a combination of 3 simple machines: – Lever Lever – Wheel & axle Wheel & axle – WedgeWedge

WORK & SIMPLE WORK & SIMPLE MACHINESMACHINES Simple machines Simple machines DON’TDON’T change change

the amount of the amount of WORKWORK done! done!(They change the size, distance (They change the size, distance or direction of your FORCE!)or direction of your FORCE!)

WORK INWORK IN = = WORK OUTWORK OUT**

(*usually machines lose a bit of (*usually machines lose a bit of work due to work due to FRICTIONFRICTION…)…)

INCLINED PLANEINCLINED PLANE

An inclined plane is a flat, sloped An inclined plane is a flat, sloped surface. It connects a lower level to a surface. It connects a lower level to a higher level.higher level.

You use less force over a longer You use less force over a longer distance to raise a load to a higher distance to raise a load to a higher level.level. Input

ForceOutput Force

INCLINED PLANE:INCLINED PLANE: Examples Examples

Ramps (Boat ramps, wheelchair Ramps (Boat ramps, wheelchair ramps)ramps)

PropellerPropeller Ladders/StairsLadders/Stairs

SCREWSCREW

A screw has a “thread” or “groove” A screw has a “thread” or “groove” wrapped around a central cylinder.wrapped around a central cylinder.

While turning, it converts a twisting While turning, it converts a twisting force into a forward or backward force into a forward or backward force. force.

Input Force

Output Force

SCREW:SCREW: Examples & Uses Examples & Uses

Screws can holds things together Screws can holds things together or lift materials.or lift materials.

ScrewsScrews Screw top lids for jars/bottlesScrew top lids for jars/bottles Light bulbLight bulb Swivel stools/chairsSwivel stools/chairs

A wedge has slanting slides that meet A wedge has slanting slides that meet at an edge – it splits material apart. at an edge – it splits material apart.

It changes force in one direction into It changes force in one direction into a splitting force that acts at right a splitting force that acts at right angles to the blade. angles to the blade.

WEDGEWEDGE

Input Force

Output ForceOutput Force

WEDGE:WEDGE: Examples & Uses Examples & Uses

Ax, Knife, etc.Ax, Knife, etc. ZippersZippers

Used in all cutting machines (to Used in all cutting machines (to split materials apart)split materials apart)

WHEEL & AXLEWHEEL & AXLE

The wheel is locked to the central axle The wheel is locked to the central axle – when one turns, so does the other – when one turns, so does the other one.one.

A short powerful force at the axle, will move A short powerful force at the axle, will move the wheel’s edge a long distance.the wheel’s edge a long distance.

A long motion at edge of wheel, moves the A long motion at edge of wheel, moves the axle with great force.axle with great force.Input

Force

Output Force

Output Force

Input Force

WHEEL & AXLE:WHEEL & AXLE: Examples & Uses Examples & Uses

ScrewdriverScrewdriver WindmillWindmill Cars/BicyclesCars/Bicycles Rolling PinRolling Pin Door KnobDoor Knob FanFan

PULLEYPULLEY

A pulley is a grooved wheel with a A pulley is a grooved wheel with a rope, used to raise/lower/move a load. rope, used to raise/lower/move a load.

Pulley systems change the direction Pulley systems change the direction and/or decrease the input force so you and/or decrease the input force so you can move heavier loads.can move heavier loads.

Output

ForceInput Force

Output Force

Input Force

PULLEY:PULLEY: Examples & Uses Examples & Uses

CranesCranes Raising a flag on a Raising a flag on a

polepole Window BlindsWindow Blinds Raising a sail on a Raising a sail on a

boatboat Clothesline Clothesline

LEVERLEVER

A lever is a bar that pivots or rotates A lever is a bar that pivots or rotates on a point (called a fulcrum). on a point (called a fulcrum).

Levers may change the size, Levers may change the size, distance or direction of the force. distance or direction of the force.

LEVERS:LEVERS: Examples & Uses Examples & Uses First Class Levers:First Class Levers:

– Scissors, See-saws, PliersScissors, See-saws, Pliers

Second Class Levers:Second Class Levers:– Staplers, Nutcrackers, Staplers, Nutcrackers, Wheelbarrows Wheelbarrows

Third Class LeversThird Class Levers– Shovels, baseball bats, tweezersShovels, baseball bats, tweezers

Machines make work easier by Machines make work easier by changing 3 things about the changing 3 things about the FORCE:FORCE:

The The amountamount of force of force

The The distancedistance of the force of the force

The The directiondirection of the force of the force

Machines make work easier by Machines make work easier by changing 3 things about the changing 3 things about the FORCE:FORCE:

The The amountamount of force of force(eg. A ramp lets you lift a heavy (eg. A ramp lets you lift a heavy

object with object with LESS forceLESS force))

Machines make work easier by Machines make work easier by changing 3 things about the changing 3 things about the FORCE:FORCE:

The The distancedistance of the force of the force(eg. A baseball bat lets you move your (eg. A baseball bat lets you move your

arms a short distance, but move the arms a short distance, but move the end of the bat a large distance).end of the bat a large distance).

Machines make work easier by Machines make work easier by changing 3 things about the changing 3 things about the FORCE:FORCE:

The The directiondirection of the force of the force(eg. The pulley on a set of window (eg. The pulley on a set of window

blinds lets you move the blinds UP blinds lets you move the blinds UP with a DOWNWARD pull.with a DOWNWARD pull.

What is the What is the mechanical advantagemechanical advantage of a machine?of a machine? A machine’s A machine’s mechanical mechanical

advantageadvantage is the number of is the number of times a machine times a machine increases a increases a forceforce exerted on it. exerted on it.

Mechanical = Mechanical = Output ForceOutput Force AdvantageAdvantage Input Force Input Force

What is the What is the mechanical advantagemechanical advantage of a machine?of a machine? You exert 10 N of force on a You exert 10 N of force on a

can opener. The can opener can opener. The can opener exerts 30 N of force on the exerts 30 N of force on the can. What is the mechanical can. What is the mechanical advantage?advantage?

Mechanical = Mechanical = Output ForceOutput Force = = 30 N30 N

AdvantageAdvantage Input Force 10 N Input Force 10 N

Mechanical Advantage = 3Mechanical Advantage = 3

What is the What is the efficiencyefficiency of a machine?of a machine? The EFFICIENCY compares: The EFFICIENCY compares:

– the the workwork you put you put ININ to to – the the workwork the machine puts the machine puts OUTOUT..

An IDEAL machine is 100% efficient.An IDEAL machine is 100% efficient. INPUT WORK = OUTPUT WORKINPUT WORK = OUTPUT WORK

In the real world, some input work is In the real world, some input work is always lost due to always lost due to FRICTIONFRICTION between between the moving parts of the machine.the moving parts of the machine.

What is the What is the efficiencyefficiency of a machine?of a machine?

EFFICIENCY = EFFICIENCY = Output WorkOutput Work x 100% x 100% Input WorkInput Work

You mow the lawn with a rusty lawn You mow the lawn with a rusty lawn mower. You do 50,000 J of work on mower. You do 50,000 J of work on the lawn mower but only 25,000 J the lawn mower but only 25,000 J go to cutting the lawn. What is the go to cutting the lawn. What is the efficiency of the lawn mower?efficiency of the lawn mower?

What is the What is the efficiencyefficiency of a machine?of a machine? You mow the lawn with a rusty lawn mower. You mow the lawn with a rusty lawn mower.

You do 50,000 J of work on the lawn mower You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower?What is the efficiency of the lawn mower?

EFFICIENCY = EFFICIENCY = Output WorkOutput Work x 100% x 100% Input Work Input Work

Efficiency = Efficiency = 25,000 J25,000 J x 100% x 100%

50,000 J50,000 J

Efficiency = 50%Efficiency = 50%

Try the rest of the Try the rest of the practice problems on practice problems on your own…your own…

Mechanical = Mechanical = Output ForceOutput Force AdvantageAdvantage Input Force Input Force

EFFICIENCY = EFFICIENCY = Output WorkOutput Work x 100% x 100% Input Work Input Work