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Simple Machines Ronald E. McNair Physical Science

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Page 1: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

Simple MachinesSimple MachinesRonald E. McNair Physical Science Ronald E. McNair Physical Science

Page 2: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

Simple MachinesSimple Machines

• Have few or no moving parts

• Make work easier• Can be combined to

create complex machines• Six simple machines:

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

• Have few or no moving parts

• Make work easier• Can be combined to

create complex machines• Six simple machines:

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

Page 3: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

LeverLever• A rigid board or rod

combined with a fulcrum and effort

• By varying position of load and fulcrum, load can be lifted or moved with less force

• Trade off: must move lever large distance to move load small distance

• There are 3 types of levers

• A rigid board or rod combined with a fulcrum and effort

• By varying position of load and fulcrum, load can be lifted or moved with less force

• Trade off: must move lever large distance to move load small distance

• There are 3 types of levers

Page 4: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

1st Class Lever1st Class Lever• The fulcrum is

located between the effort and the load

• Direction of force always changes

• Examples are scissors, pliers, and crowbars

• The fulcrum is located between the effort and the load

• Direction of force always changes

• Examples are scissors, pliers, and crowbars

Page 5: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

2nd Class Lever2nd Class Lever• The resistance is

located between the fulcrum and the effort

• Direction of force does not change

• Examples include bottle openers and wheelbarrows

• The resistance is located between the fulcrum and the effort

• Direction of force does not change

• Examples include bottle openers and wheelbarrows

Page 6: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

3rd Class Lever3rd Class Lever• The effort is

located between the fulcrum and the resistance

• Direction of force does not change, but a gain in speed always happens

• Examples include ice tongs, tweezers and shovels

• The effort is located between the fulcrum and the resistance

• Direction of force does not change, but a gain in speed always happens

• Examples include ice tongs, tweezers and shovels

Page 7: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Mechanical AdvantageMechanical Advantage• We know that a machine multiplies whatever

force you put into it: - Using a screwdriver to turn a screw - Twisting a nail with pliers - Carrying a box up a ramp instead

of stairs• The amount that the machine multiplies that

force is the mechanical advantage of the machine

• Abbreviated MA

• We know that a machine multiplies whatever force you put into it:

- Using a screwdriver to turn a screw - Twisting a nail with pliers - Carrying a box up a ramp instead

of stairs• The amount that the machine multiplies that

force is the mechanical advantage of the machine

• Abbreviated MA

Page 8: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Mechanical AdvantageMechanical Advantage

• (IMA) Ideal MA: This is the MA of a machine in a world with no friction, and no force is lost anywhere

• (AMA) Actual MA: This is simply the MA of a machine in the world as we know it

- Force is lost due to friction - Force is lost due to wind,

etc.

• Can we have an ideal machine?

• (IMA) Ideal MA: This is the MA of a machine in a world with no friction, and no force is lost anywhere

• (AMA) Actual MA: This is simply the MA of a machine in the world as we know it

- Force is lost due to friction - Force is lost due to wind,

etc.

• Can we have an ideal machine?

Page 9: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Mechanical Advantage: LeverMechanical Advantage: Lever

• The mechanical advantage of a lever is the distance from the effort to the fulcrum divided by the distance from the fulcrum to the load

• For our example, MA = 10/5 = 2

• The mechanical advantage of a lever is the distance from the effort to the fulcrum divided by the distance from the fulcrum to the load

• For our example, MA = 10/5 = 2

• Distance from effort to fulcrum: 10 feet

• Distance from load to fulcrum: 5 feet

MA =Distance, effort - fulcrumDistance, load - fulcrum

Page 10: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Inclined PlanesInclined Planes• A slope or ramp that

goes from a lower to higher level

• Makes work easier by taking less force to lift something a certain distance

• Trade off: the distance the load must be moved would be greater than simply lifting it straight up

• A slope or ramp that goes from a lower to higher level

• Makes work easier by taking less force to lift something a certain distance

• Trade off: the distance the load must be moved would be greater than simply lifting it straight up

Page 11: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Mechanical Advantage: Inclined PlaneMechanical Advantage: Inclined Plane• The mechanical

advantage of an inclined plane is the length of the slope divided by the height of the plane, if effort is applied parallel to the slope

• So for our plane MA = 15 feet/3 feet

= 5

• The mechanical advantage of an inclined plane is the length of the slope divided by the height of the plane, if effort is applied parallel to the slope

• So for our plane MA = 15 feet/3 feet

= 5

• Let’s say S = 15 feet, H = 3 feet

MA =Length of SlopeHeight of Plane

Page 12: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Wheel and AxleWheel and Axle• A larger circular wheel

affixed to a smaller rigid rod at its center

• Used to translate force across horizontal distances (wheels on a wagon) or to make rotations easier (a doorknob)

• Trade off: the wheel must be rotated through a greater distance than the axle

• A larger circular wheel affixed to a smaller rigid rod at its center

• Used to translate force across horizontal distances (wheels on a wagon) or to make rotations easier (a doorknob)

• Trade off: the wheel must be rotated through a greater distance than the axle

Page 13: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Mechanical Advantage: Wheel and AxleMechanical Advantage: Wheel and Axle

• The mechanical advantage of a wheel and axle system is the radius of the wheel divided by the radius of the axle

• So for our wheel and axle MA = 10”/2” = 5

• The mechanical advantage of a wheel and axle system is the radius of the wheel divided by the radius of the axle

• So for our wheel and axle MA = 10”/2” = 5

2"

10"

MA =Radius of WheelRadius of Axle

Page 14: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

ScrewScrew

• An inclined plane wrapped around a rod or cylinder

• Used to lift materials or bind things together

• An inclined plane wrapped around a rod or cylinder

• Used to lift materials or bind things together

Page 15: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Mechanical Advantage: Screw

Mechanical Advantage: Screw

• The Mechanical advantage of a screw is the circumference of the screwdriver divided by the pitch of the screw

• The pitch of the screw is the number of threads per inch

• So for our screwdriver

MA = 3.14”/0.1” = 31.4

• The Mechanical advantage of a screw is the circumference of the screwdriver divided by the pitch of the screw

• The pitch of the screw is the number of threads per inch

• So for our screwdriver

MA = 3.14”/0.1” = 31.4

Diam.=1"

10 threadsper inch

Circumference = ∏ x 1” = 3.14”

Pitch = 1/10” = 0.1”

MA = Circumference of ScrewdriverPitch of Screw

Page 16: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

WedgeWedge• An inclined plane on

its side• Used to cut or force

material apart• Often used to split

lumber, hold cars in place, or hold materials together (nails)

• An inclined plane on its side

• Used to cut or force material apart

• Often used to split lumber, hold cars in place, or hold materials together (nails)

Page 17: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Mechanical Advantage: Wedge

Mechanical Advantage: Wedge

• Much like the inclined plane, the mechanical advantage of a wedge is the length of the slope divided by the width of the widest end

• So for our wedge, MA = 6”/2” = 3• They are one of the

least efficient simple machines

• Much like the inclined plane, the mechanical advantage of a wedge is the length of the slope divided by the width of the widest end

• So for our wedge, MA = 6”/2” = 3• They are one of the

least efficient simple machines

2"

6"

MA = Length of SlopeThickness of Widest End

Page 18: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

PulleyPulley• A rope or chain free to turn

around a suspended wheel• By pulling down on the

rope, a load can be lifted with less force

• Trade off: no real trade off here; the secret is that the pulley lets you work with gravity so you add the force of your own weight to the rope

• A rope or chain free to turn around a suspended wheel

• By pulling down on the rope, a load can be lifted with less force

• Trade off: no real trade off here; the secret is that the pulley lets you work with gravity so you add the force of your own weight to the rope

Page 19: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Mechanical Advantage: Pulley

Mechanical Advantage: Pulley

• The Mechanical Advantage of a pulley is equal to the number of ropes supporting the pulley

• So for the pulley system shown there are 3 ropes supporting the bottom pulley

MA = 3• This means that if

you pull with a force of 20 pounds you will lift an object weighing 60 pounds

• The Mechanical Advantage of a pulley is equal to the number of ropes supporting the pulley

• So for the pulley system shown there are 3 ropes supporting the bottom pulley

MA = 3• This means that if

you pull with a force of 20 pounds you will lift an object weighing 60 pounds

Page 20: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

The trick is WORKThe trick is WORK

• Simple machines change the amount of force needed, but they do not change the amount of work done

• What is work?• Work equals force times distance• W = F x d

• By increasing the distance, you can decrease the force and still do the same amount of work

• Simple machines change the amount of force needed, but they do not change the amount of work done

• What is work?• Work equals force times distance• W = F x d

• By increasing the distance, you can decrease the force and still do the same amount of work

Page 21: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

Examples:Examples: • Lever: • Work is equal on both sides

of a lever. You move the long end a LARGE distance with SMALL force. The other end moves a SMALL distance with a LARGE force, which is why it can lift heavy objects.

• Lever: • Work is equal on both sides

of a lever. You move the long end a LARGE distance with SMALL force. The other end moves a SMALL distance with a LARGE force, which is why it can lift heavy objects.

•Inclined Plane: •It takes a certain amount of work to get the cabinet into the truck. You can either exert a LARGE force to lift it the SMALL distance into the truck, or you can exert a SMALL force to move it a LARGE distance along the ramp.

Page 22: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

EfficiencyEfficiency• The efficiency is a ratio that measures how much

work the machine produces versus how much work goes in

• Example: We have an inclined plane with an ideal MA of 3. We measure our real-life inclined plane and find an MA of 2. Efficiency = Actual MA/Ideal MA x 100% = (2/3) X 100% = 66.66%

• The efficiency is a ratio that measures how much work the machine produces versus

how much work goes in

• Example: We have an inclined plane with an ideal MA of 3. We measure our real-life inclined plane and find an MA of 2. Efficiency = Actual MA/Ideal MA x 100% = (2/3) X 100% = 66.66%

Efficiency =Work OutputWork Input

X 100%

Efficiency = Actual MAIdeal MA

Page 23: Simple Machines Simple Machines Ronald E. McNair Physical Science Ronald E. McNair Physical Science

NSF North Mississippi GK8NSF North Mississippi GK8

SourcesSourcesCOSI.org. 2006. Simple Machines. Accessed 3 February 2006. http://www.cosi.org/onlineExhibits/simpMach/sm1.html

Jones, Larry. January 2006. Science by Jones: Levers. Accessed 2 February 2006. http://www.sciencebyjones.com/secondclasslevers.htm

Mikids.com. 2006. Simple Machines. Accessed 2 February 2006. http://www.mikids.com/Smachines.htm

Professor Beaker’s Learning Labs. August 2004. Simple Machines: inclined planes. Accessed 2 February 2006. http://www.professorbeaker.com/planefact.html

Wikepedia. Accessed 3 February 2006. http://en.wikipedia.org/wiki/Mechanicaladvantage