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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
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)
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
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
Key TermsKey TermsEfficiency (a ratio)
◦Is calculated using the following equations:
◦Actual mechanical advantage/idealized mechanical advantage
◦Useful work output/total work input
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
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
Simple MachinesSimple MachinesTwo families
Lever Inclined plane--Lever
--Pulley
--Wheel and axle
--Ramp
--Wedge
--Screw
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
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.
Which lever would have the highest mechanical advantage and why?
a
b
cb has the largest input distance, giving the largest MA