machines and efficiency
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MACHINES and EFFICIENCY. Chapter 9.8-9.9. Key Terms. Work = Force x distance Simple machine a device used to multiply forces or change the direction of forces Compound machine A machine composed of two or more simple machines. Key Terms. Input (effort) - PowerPoint PPT PresentationTRANSCRIPT
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MACHINES and MACHINES and EFFICIENCYEFFICIENCYChapter 9.8-9.9
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Key TermsKey TermsWork = Force x distanceSimple machine
◦a device used to multiply forces or change the direction of forces
Compound machine◦A machine composed of two or more
simple machines
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Key TermsKey TermsInput (effort)
◦Input distance: the distance you input the force when using a machine
◦Input force: the force you use when using a machine
Output (resistance)◦Output distance: the distance the
object that work is done on moves◦Output force: the force required to
move the object without a machine (usually the weight of the object in newtons)
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Key TermsKey TermsMechanical Advantage (MA)
◦A unitless ratio that indicates the number of times a machine multiplies your input force
Ideal Mechanical Advantage (IMA)◦The calculated MA, does not consider
frictionActual Mechanical Advantage (AMA)
◦The measured or real MA, does consider friction
Because of friction, AMA < IMA
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A simple machineA simple machineMultiplies and redirects forceDoes not reduce the amount of
work to be done, but makes work easier.
MA > 1 means that your input force will be less than your output force
More leverage means more mechanical advantage
If you increase MA, then◦Input force will decrease◦Input distance will increase
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Key TermsKey TermsEfficiency (a ratio)
◦Is calculated using the following equations:
◦Actual mechanical advantage/idealized mechanical advantage
◦Useful work output/total work input
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Key TermsKey TermsEfficiency of a machine decreases
as friction increases◦Friction increases the thermal energy
by increasing molecular KE (non-mechanical energy)
◦In other words… friction causes the particles to speed up, raising the average KE of the particles (and temperature!)
◦Friction causes the useful work output to be less than the total work input
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Key TermsKey TermsWhen using a machine…
◦Work is done to move the object ◦Work is done against frictionUseful work output is the work done to move the object
Total work input is work done to move object + work done against friction
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Simple MachinesSimple MachinesTwo families
Lever Inclined plane--Lever
--Pulley
--Wheel and axle
--Ramp
--Wedge
--Screw
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fulcrum
The Lever
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Three Classes of LeversThree Classes of LeversFirst class
Examples:
Crowbar
See-saw
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Three Classes of LeverThree Classes of LeverSecond class
Examples:
Wheelbarrow
Door
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Three Classes of LeverThree Classes of LeverThird class
Examples:
Human arm
Baseball bat
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Calculating the Mechanical Calculating the Mechanical Advantage of a LeverAdvantage of a LeverMA = input distance/output
distance which is…MA = length of effort arm/length of resistance arm.
Effort armResistance arm
2.5 m
0.5 mEffort or input distance
Resistance or output distance
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Calculating the Mechanical Calculating the Mechanical Advantage of a LeverAdvantage of a Lever2nd class lever
3rd class lever
3rd class levers reduce the output force, but increase output distance and speed
2nd class levers decrease the input force but increase the input distance.
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Which lever would have the highest mechanical advantage and why?
a
b
cb has the largest input distance, giving the largest MA
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PulleyPulley
Fixed pulley
1 support rope
IMA = 1
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PulleysPulleys
IMA = 2
Two supporting ropes
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PulleysPulleys
IMA = ?
2
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PulleyPulleyHow many support ropes?
4
What is the IMA?
4
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Wheel and AxleWheel and AxleWheel connected to a shaft
GIVES YOU LEVERAGE
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Inclined planesInclined planesRamps
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WedgeWedgeTwo inclined planes stuck
together
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ScrewScrewAn inclined plane wrapped
around a cylinder
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What type of machine is What type of machine is this?this?
Compound: made of two or more machines
Two 1st class levers; two wedges (scissor blades)