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Simple Machines and Simple Machines and Mechanical AdvantageMechanical Advantage
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Remember Work?Remember Work?
Remember:Remember:WorkWork = using a force to move an = using a force to move an object some distance (in the same object some distance (in the same direction as the applied force.)direction as the applied force.)
Formula for workFormula for workWork = Force x DistanceWork = Force x DistanceW = FdW = Fd
Unit of Work = Newton*meter = Unit of Work = Newton*meter = JouleJoule
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What’s work?What’s work? A scientist delivers a speech to an A scientist delivers a speech to an
audience of his peers. audience of his peers. A body builder lifts 350 pounds A body builder lifts 350 pounds
above his head. above his head. A mother carries her baby from room A mother carries her baby from room
to room. to room. A father pushes a baby in a carriage.A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag A woman carries a 20 kg grocery bag
to her car? to her car?
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What’s work?What’s work? A scientist delivers a speech to an A scientist delivers a speech to an
audience of his peers. audience of his peers. NoNo A body builder lifts 350 pounds A body builder lifts 350 pounds
above his head. above his head. YesYes A mother carries her baby from room A mother carries her baby from room
to room. to room. NoNo A father pushes a baby in a carriage. A father pushes a baby in a carriage. YesYes A woman carries a 20 km grocery A woman carries a 20 km grocery
bag to her car? bag to her car? NoNo
Simple machines are tools used to make work
easier.
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Simple MachinesSimple Machines
Simple machine Simple machine = a device that = a device that helps make work easier to perform helps make work easier to perform by accomplishing by accomplishing one or more one or more of of the following functions: the following functions: transferring a force from one place to
another, changing the direction of a force, increasing the magnitude of a force, or increasing the distance or speed of a
force.
You have probably used some simple machines, but did not realize that they were
actually called simple machines!
Simple machines do not make less work; they just make
it easier to do work.
It would be hard to cut this wood without the saw!
Simple Machines:Simple Machines:Work input and outputWork input and output
Work input = Work input = amount of work done amount of work done onon (applied (applied to) a machine. to) a machine. WWinputinput = Input force x input distance = Input force x input distance
Work output = Work output = amount of work done amount of work done byby a a machine.machine. WWoutputoutput = Output force x output distance = Output force x output distance
For Ideal machines (no friction)Wout = Win
Fout x Dout = Fin x Din
10N x 3m = 2N x 15m
15 m
3 m
10 N Fin
DinDout
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Mechanical AdvantageMechanical Advantage Input forceInput force = force YOU apply (to = force YOU apply (to
machine)machine) OutputOutput forceforce = force that the machine = force that the machine
applies to the object/task (resistance).applies to the object/task (resistance). ((AActual ) ctual ) MMechanical echanical AAdvantage dvantage = the = the
ratio of the output force divided by input ratio of the output force divided by input force.force. AMA = OUTPUT (Resistance/Load) Force
INPUT (Effort) Force If the output force >the input force, If the output force >the input force,
the machine has a mechanical advantage > 1.the machine has a mechanical advantage > 1.
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Mechanical AdvantageMechanical Advantage If a machine increases an If a machine increases an input input
force of 10 Newtons force of 10 Newtons to an to an output output force of 100 Newtonsforce of 100 Newtons, the , the machine has a machine has a mechanical advantage (AMA) of mechanical advantage (AMA) of 10 10
[= 100 / [= 100 / 10]10]. .
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Mechanical AdvantageMechanical Advantage For machines that increase DISTANCE For machines that increase DISTANCE
instead of force, the instead of force, the ((IIdeal) deal) MMechanical echanical AAdvantage dvantage = ratio = ratio of output distance divided by input dist.of output distance divided by input dist. IMA = ____INPUT (Effort) Distance_______
OUTPUT (Resistance/Load) Distance
If a machine converts an If a machine converts an input distance of 6 m input distance of 6 m to an to an output distance of 2 moutput distance of 2 m, it has an , it has an IMA of 3 [= 6 / 2]IMA of 3 [= 6 / 2]. .
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Mechanical AdvantageMechanical Advantage
No machine can No machine can increase increase BOTH BOTH the the magnitude and the magnitude and the distance of a force at distance of a force at the same time.the same time.
The 6 Simple MachinesThe 6 Simple Machines
Lever
PulleyWheel and Axle
WedgeScrewInclined Plane
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Simple MachinesSimple Machines
The six simple machines are:The six simple machines are: Inclined Plane Inclined Plane
Screw Screw Wedge Wedge
Lever Lever Pulley Pulley Wheel and Axle Wheel and Axle
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1. 1. Inclined PlaneInclined Plane
Inclined plane Inclined plane = = an even sloping an even sloping surface. surface.
makes it easier to makes it easier to move a weight move a weight from a lower to from a lower to higher elevation.higher elevation.
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1. Inclined Plane1. Inclined Plane Mechanical Advantage of an inclined
plane MA = __Length of the Slope__ Height of Inclined Plane
It produces a mechanical advantage (need less force to move object) by increasing the distance through which the force must move.
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Although it takes less force for car A to get to the top of the ramp, Although it takes less force for car A to get to the top of the ramp, all the cars do the same amount of work.all the cars do the same amount of work.
A B C
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Although it takes less force for car A to get to the top of the ramp, Although it takes less force for car A to get to the top of the ramp, all the cars do the same amount of work.all the cars do the same amount of work.
A B C
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2. Screw2. Screw
SCREW = The threads of a SCREW = The threads of a screw are a circular rampscrew are a circular ramp an inclined plane an inclined plane
wrapped around a shaft wrapped around a shaft or cylinderor cylinder
allows the screw to allows the screw to move itself when move itself when rotated. rotated.
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2. Screw2. Screw
Mechanical Advantage of an screw = Number of Turns in the Threads Length of the Threads
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3. 3. WedgeWedge Wedge = 2 inclined Wedge = 2 inclined
planes joined back to planes joined back to back. back. used to split things or used to split things or
as holding devices. as holding devices.
3. 3. WedgeWedgeMechanical AdvantageMechanical Advantage
Mechanical Advantage of a wedge Mechanical Advantage of a wedge MA = MA = length of either slope (S)length of either slope (S) thickness (T) of the big end. thickness (T) of the big end.
Ex: If the length of the slope is 10 cm Ex: If the length of the slope is 10 cm & the thickness is 4 cm. Then, & the thickness is 4 cm. Then, MA = 10 / 4 = 2.5 MA = 10 / 4 = 2.5
As with the inclined plane, MA (less As with the inclined plane, MA (less force needed) is gained by the force needed) is gained by the increase in distance (T increase in distance (T S). S).
TS
S
4. LEVER
LEVER = a rigid bar (straight or curved) that moves about a fixed point
(fulcrum).
A lever is used to push, pull, or lift things.
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4. 4. LeversLevers a lever has both ana lever has both an
Effort (applied) force Effort (applied) force and a and a Load (Resistance) force Load (Resistance) force
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The 3 Classes of LeversThe 3 Classes of Levers
The class of a lever The class of a lever is determined by is determined by the location of the the location of the effort force, load, effort force, load, and the and the fulcrum fulcrum (pivot point). (pivot point).
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Mechanical Advantage of a lever = Output force [Load/Resistance] Input force [Effort] or = Length of the Effort (Input) arm Length of the Resistance (Load) arm
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First Class LeverFirst Class Lever
the fulcrum is in the middle and the load and the fulcrum is in the middle and the load and effort are on opposite sideseffort are on opposite sides.. Common examples include Common examples include
crowbars, scissors, pliers, tin snips and crowbars, scissors, pliers, tin snips and seesaws. seesaws.
A first-class lever always changes the A first-class lever always changes the direction of force direction of force (I.e. downward effort force (I.e. downward effort force = upward movement of = upward movement of Load( resistance). Load( resistance).
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Fulcrum is between EF (effort) and RF (load)Fulcrum is between EF (effort) and RF (load)Effort moves farther than Resistance.Effort moves farther than Resistance. Multiplies EF and changes its direction Multiplies EF and changes its direction
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Second Class LeverSecond Class Lever
the fulcrum is at the end, with the the fulcrum is at the end, with the load in the middleload in the middle
Examples include nut crackers, wheel Examples include nut crackers, wheel barrows, doors, and bottle openers.barrows, doors, and bottle openers.
Does Does NOT NOT change the direction of force. change the direction of force. Effort moves farther than Resistance Effort moves farther than Resistance
(Load)(Load) Results in an Results in an
Increase in Force (mechanical advantage). Increase in Force (mechanical advantage).
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Resistance Force (load) is between fulcrum and Effort ForceResistance Force (load) is between fulcrum and Effort Force
Effort moves farther than Resistance.Effort moves farther than Resistance.
Multiplies Effort Force, but does NOT change its directionMultiplies Effort Force, but does NOT change its direction
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Third Class LeverThird Class Lever
Effort force is applied between the Effort force is applied between the fulcrum and the resistance force.fulcrum and the resistance force. Examples include tweezers, hammers, Examples include tweezers, hammers,
and shovels tongs, or a human arm, and shovels tongs, or a human arm, fishing pole, baseball batfishing pole, baseball bat
Does NOT change the direction of force; Does NOT change the direction of force; Produce a Produce a gain in speed and distance gain in speed and distance
and a corresponding and a corresponding decrease in forcedecrease in force. .
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Effort Force is between fulcrum and Resistance Force (load)Effort Force is between fulcrum and Resistance Force (load)
Does not Multiply Force or Change it’s direction Does not Multiply Force or Change it’s direction
Resistance moves farther than Effort.Resistance moves farther than Effort.
Multiplies the distance the effort force travelsMultiplies the distance the effort force travels
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5. 5. Wheel and Wheel and AxleAxle
Wheel and AxleWheel and Axle a large wheel a large wheel rigidly secured to rigidly secured to a smaller shaft a smaller shaft (axle). (axle).
Turning the wheel Turning the wheel also turns the axlealso turns the axle
Turning the axle Turning the axle also turns the also turns the wheelwheel
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5. 5. Wheel and AxleWheel and Axle
Wheel and AxleWheel and Axle acts like acts like 22ndnd class or 3class or 3rdrd class LEVER class LEVER depending on if the Effort Force is depending on if the Effort Force is Applied to the axle or the wheelApplied to the axle or the wheel
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5. 5. Wheel and AxleWheel and Axle Gears are sets of Wheel and Gears are sets of Wheel and
Axles that mesh togetherAxles that mesh together One gear turns the next IN One gear turns the next IN
THE OPPOSITE DIRECTIONTHE OPPOSITE DIRECTION
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6. 6. PulleyPulley Pulley are wheels and Pulley are wheels and
axles with a groove axles with a groove around the outsidearound the outside Can act as 1Can act as 1stst or 2 or 2ndnd
class levers.class levers. Can simply change the Can simply change the
direction of a force ORdirection of a force ORgain a mechanical gain a mechanical advantageadvantage
Examples : flagpole, clothesline, cranes, fishing reel
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6. 6. PulleyPulley fixed pulleyfixed pulley - does not rise or fall with the - does not rise or fall with the
load. (changes direction of force). load. (changes direction of force). moveable pulleymoveable pulley rises and falls with the load rises and falls with the load
being moved.(creates a mechanical being moved.(creates a mechanical advantage) advantage) Mechanical advantage = # of ropes that support Mechanical advantage = # of ropes that support
the moveable pulley (2 ropes = MA of 2). the moveable pulley (2 ropes = MA of 2).
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Efficiency Remember: We said
Input Force x Input Distance = Output Force x Output DistanceHowever, Some Output force is
lost due to friction. Efficiency compares the work output to
the input. (is a percentage) Efficiency = Work OUTPUT x 100
Work INPUT No machine has 100 percent efficiency
due to friction.
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Practice QuestionsPractice Questions1. Explain who is doing more work and why: a bricklayer 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and being constructed, or a project supervisor observing and recording the progress of the workers from an observation recording the progress of the workers from an observation booth. booth.
2. How much work is done in pushing an object 7.0 m across 2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is original position? How much power is used if this work is done in 20 sec?done in 20 sec?
3. Using a single fixed pulley, how heavy a load could you 3. Using a single fixed pulley, how heavy a load could you liftlift??
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Practice QuestionsPractice Questions
4.4. Give an example of a machine in which friction is Give an example of a machine in which friction is both an advantage and a disadvantage.both an advantage and a disadvantage.
5. Why is it not possible to have a machine with 5. Why is it not possible to have a machine with 100% efficiency?100% efficiency?
6. What is effort force? What is work input? Explain 6. What is effort force? What is work input? Explain the relationship between effort force, effort the relationship between effort force, effort distance, and work input. distance, and work input.
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Practice QuestionsPractice Questions1. Explain who is doing more work and why: a bricklayer carrying 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. progress of the workers from an observation booth. Work is defined as a force applied to an object, moving that object a distance in the direction of the applied force. The bricklayer is doing more work.
2. How much work is done in pushing an object 7.0 m across a 2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? position? How much power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700 N-m or J; Power = 700 N-m/20 sec = 35 W
3. Using a single fixed pulley, how heavy a load could you lift?3. Using a single fixed pulley, how heavy a load could you lift?Since a fixed pulley has a mechanical advantage of one, it will only change the direction of the force applied to it. You would be able to lift a load equal to your own weight, minus the negative effects of friction.
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Practice QuestionsPractice Questions4. 4. Give an example of a machine in which friction is both an Give an example of a machine in which friction is both an
advantage and a disadvantage. advantage and a disadvantage. One answer might be the use of a car jack. Advantage of friction: It allows a car to be raised to a desired height without slipping. Disadvantage of friction: It reduces efficiency.
5. Why is it not possible to have a machine with 100% efficiency? 5. Why is it not possible to have a machine with 100% efficiency? Friction lowers the efficiency of a machine. Work output is always less than work input, so an actual machine cannot be 100% efficient.
6. What is effort force? What is work input? Explain the relationship 6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input. between effort force, effort distance, and work input. The effort force is the force applied to a machine. Work input is the work done on a machine. The work input of a machine is equal to the effort force times the distance over which the effort force is exerted.
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Inclined PlaneInclined Plane
Inclined plane Inclined plane = = an even sloping an even sloping surface. surface.
makes it easier to makes it easier to move a weight move a weight from a lower to from a lower to higher elevation.higher elevation.
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Inclined PlaneInclined Plane Mechanical Advantage of an inclined
plane = __Length of the Slope__ Height of Inclined Plane
It produces a mechanical advantage (need less force to move object) by increasing the distance through which the force must move.
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Although it takes less force for car A to get to the top of the ramp, Although it takes less force for car A to get to the top of the ramp, all the cars do the same amount of work.all the cars do the same amount of work.
A B C
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Inclined PlaneInclined Plane A wagon trail on a A wagon trail on a
steep hill will often steep hill will often traverse back and forth traverse back and forth to reduce the slope to reduce the slope experienced by a team experienced by a team pulling a heavily loaded pulling a heavily loaded wagon.wagon.
This same technique is This same technique is used today in modern used today in modern freeways which travel freeways which travel winding paths through winding paths through steep mountain passes. steep mountain passes.
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WedgeWedge The wedge is a The wedge is a
modification of the inclined modification of the inclined plane. Wedges are used as plane. Wedges are used as either separating or either separating or holding devices. holding devices.
A wedge can either be A wedge can either be composed of one or two composed of one or two inclined planes. A double inclined planes. A double wedge can be thought of wedge can be thought of as two inclined planes as two inclined planes joined together with their joined together with their sloping surfaces outward. sloping surfaces outward.
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ScrewScrew
The screw is also a The screw is also a modified version of modified version of the inclined plane. the inclined plane.
While this may be While this may be somewhat difficult somewhat difficult to visualize, it may to visualize, it may help to think of the help to think of the threads of the threads of the screw as a type of screw as a type of circular ramp (or circular ramp (or inclined plane). inclined plane).
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MA of an screw can be calculated by dividing the number of turns per inch.
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EfficiencyEfficiency Remember: We saidRemember: We said
Input Force x Input Distance Input Force x Input Distance = Output Force x Output = Output Force x Output DistanceDistanceHowever, Some Output force is
lost due to friction. EfficiencyEfficiency compares the work output to compares the work output to
the input. (is a percentage)the input. (is a percentage) Efficiency Efficiency = = Work OUTPUT Work OUTPUT x 100 x 100
Work INPUT Work INPUT No machine has 100 percent efficiency
due to friction.
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Practice QuestionsPractice Questions1. Explain who is doing more work and why: a bricklayer 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and being constructed, or a project supervisor observing and recording the progress of the workers from an observation recording the progress of the workers from an observation booth. booth.
2. How much work is done in pushing an object 7.0 m across 2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is original position? How much power is used if this work is done in 20 sec?done in 20 sec?
3. Using a single fixed pulley, how heavy a load could you 3. Using a single fixed pulley, how heavy a load could you liftlift??
5454
Practice QuestionsPractice Questions
4.4. Give an example of a machine in which friction is Give an example of a machine in which friction is both an advantage and a disadvantage.both an advantage and a disadvantage.
5. Why is it not possible to have a machine with 5. Why is it not possible to have a machine with 100% efficiency?100% efficiency?
6. What is effort force? What is work input? Explain 6. What is effort force? What is work input? Explain the relationship between effort force, effort the relationship between effort force, effort distance, and work input. distance, and work input.
5555
Practice QuestionsPractice Questions1. Explain who is doing more work and why: a bricklayer carrying 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. progress of the workers from an observation booth. Work is defined as a force applied to an object, moving that object a distance in the direction of the applied force. The bricklayer is doing more work.
2. How much work is done in pushing an object 7.0 m across a 2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? position? How much power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700 N-m or J; Power = 700 N-m/20 sec = 35 W
3. Using a single fixed pulley, how heavy a load could you lift?3. Using a single fixed pulley, how heavy a load could you lift?Since a fixed pulley has a mechanical advantage of one, it will only change the direction of the force applied to it. You would be able to lift a load equal to your own weight, minus the negative effects of friction.
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Practice QuestionsPractice Questions4. 4. Give an example of a machine in which friction is both an Give an example of a machine in which friction is both an
advantage and a disadvantage. advantage and a disadvantage. One answer might be the use of a car jack. Advantage of friction: It allows a car to be raised to a desired height without slipping. Disadvantage of friction: It reduces efficiency.
5. Why is it not possible to have a machine with 100% efficiency? 5. Why is it not possible to have a machine with 100% efficiency? Friction lowers the efficiency of a machine. Work output is always less than work input, so an actual machine cannot be 100% efficient.
6. What is effort force? What is work input? Explain the relationship 6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input. between effort force, effort distance, and work input. The effort force is the force applied to a machine. Work input is the work done on a machine. The work input of a machine is equal to the effort force times the distance over which the effort force is exerted.
