Simple Machines Simple Machines Matt Aufman and Steve Case University of Mississippi NSF NMGK-8...
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Transcript of Simple Machines Simple Machines Matt Aufman and Steve Case University of Mississippi NSF NMGK-8...
Simple MachinesSimple MachinesMatt Aufman and Steve Case
University of MississippiNSF NMGK-8
February 2006
Matt Aufman and Steve CaseUniversity of Mississippi
NSF NMGK-8February 2006
NSF North Mississippi GK8NSF North Mississippi GK8
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
NSF North Mississippi GK8NSF North Mississippi GK8
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
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.
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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
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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
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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
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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
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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?
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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, IMA = 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, IMA = 10/5 = 2
• Distance from effort to fulcrum: 10 feet
• Distance from load to fulcrum: 5 feet
MA =Distance, effort - fulcrumDistance, load - fulcrum
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Mechanical Advantage : Lever
Mechanical Advantage : Lever
• Actual Mechanical Adv (AMA) Load = 3 NEffort force needed to life load = 2 N
AMA = 3N / 2N = 1.5
• Actual Mechanical Adv (AMA) Load = 3 NEffort force needed to life load = 2 N
AMA = 3N / 2N = 1.5
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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
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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 IMA = 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 IMA = 15 feet/3 feet
= 5
• Let’s say S = 15 feet, H = 3 feet
MA =Length of SlopeHeight of Plane
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Actual Mechanical Advantage
Actual Mechanical Advantage
Force to liftForce to slide up the ramp
AMA =5N/2.5 to slide = 2
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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.
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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
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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