Simple MachinesSimple MachinesThey make life easy breezy…They make life easy breezy…

Simple MachinesSimple MachinesAncient people invented simple Ancient people invented simple

machines that would help them overcome machines that would help them overcome resistive forces and allow them to do the resistive forces and allow them to do the desired work against those forces. desired work against those forces.

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Simple MachinesSimple Machines

The six simple machines are:The six simple machines are: Lever Lever Wheel and Axle Wheel and Axle Pulley Pulley Inclined Plane Inclined Plane Wedge Wedge Screw Screw

Simple MachinesSimple Machines

A machine is a device that helps make A machine is a device that helps make work easier to perform by accomplishing work easier to perform by accomplishing one or more of the following functions: one or more of the following functions:

transferring a force from one place to another, transferring a force from one place to another, changing the direction of a force, changing the direction of a force, increasing the magnitude of a force, or increasing the magnitude of a force, or increasing the distance or speed of a force. increasing the distance or speed of a force.

Mechanical AdvantageMechanical Advantage

It is useful to think about a machine in It is useful to think about a machine in terms of the terms of the input forceinput force (the force you (the force you apply) and the apply) and the outputoutput forceforce (force which (force which is applied to the task).is applied to the task).

When a machine takes a small input force When a machine takes a small input force and increases the magnitude of the output and increases the magnitude of the output force, a force, a mechanical advantagemechanical advantage has been has been produced. produced.

Mechanical AdvantageMechanical Advantage Mechanical advantage is the ratio of output force Mechanical advantage is the ratio of output force

divided by input force. If the output force is bigger divided by input force. If the output force is bigger than the input force, a machine has a mechanical than the input force, a machine has a mechanical advantage greater than one.advantage greater than one.

If a machine increases an input force of 10 pounds If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10. a mechanical advantage (MA) of 10.

In machines that increase distance instead of In machines that increase distance instead of force, the MA is the ratio of the output distance and force, the MA is the ratio of the output distance and input distance.input distance.

MA = output/input MA = output/input

IMA vs AMAIMA vs AMA

NOTE: There is a difference between the NOTE: There is a difference between the calculated IDEAL mechanical advantage calculated IDEAL mechanical advantage (IMA) and the ACTUAL mechanical (IMA) and the ACTUAL mechanical advantage (AMA), due to the loss of advantage (AMA), due to the loss of energy from friction and heat. energy from friction and heat.

IMA is calculated, AMA is measured in real IMA is calculated, AMA is measured in real experiments. experiments.

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Limits of machinesLimits of machines

No machine can increase No machine can increase bothboth the the magnitudemagnitude and and the the distancedistance of a force at of a force at the same time.the same time.

The LeverThe Lever

A lever is a rigid bar A lever is a rigid bar that rotates around a that rotates around a fixed point called the fixed point called the fulcrum.fulcrum.

The bar may be either The bar may be either straight or curved.straight or curved.

In use, a lever has both In use, a lever has both an effort (or applied) an effort (or applied) force and a load force and a load (resistant force). (resistant force).

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The Three Classes of LeversThe Three Classes of Levers

To find the MA of a lever, divide the output force by the input force, or divide the length of the resistance arm by the length of the effort arm.

The class of a lever is determined by the location of the effort force and the load relative to the fulcrum.

First Class LeverFirst Class Lever In a first-class lever the fulcrum is In a first-class lever the fulcrum is

located at some point between the located at some point between the effort and resistance forces.effort and resistance forces. Common examples of first-class Common examples of first-class

levers include crowbars, scissors, levers include crowbars, scissors, pliers, tin snips and seesaws. pliers, tin snips and seesaws.

A first-class lever always changes A first-class lever always changes the the directiondirection of force (I.e. a of force (I.e. a downward effort force on the downward effort force on the lever results in an upward lever results in an upward movement of the resistance movement of the resistance force). force).

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

Second Class LeverSecond Class Lever With a second-class lever, the load With a second-class lever, the load

is located between the fulcrum and is located between the fulcrum and the effort force.the effort force.

Common examples of second-class Common examples of second-class levers include nut crackers, wheel levers include nut crackers, wheel barrows, doors, and bottle openers.barrows, doors, and bottle openers.

A second-class lever A second-class lever does not does not change the direction change the direction of force. When of force. When the fulcrum is located closer to the the fulcrum is located closer to the load than to the effort force, an load than to the effort force, an increase in force (mechanical increase in force (mechanical advantage) results. advantage) results.

RF (load) is between fulcrum and EF RF (load) is between fulcrum and EF Effort moves farther than Resistance.Effort moves farther than Resistance.

Multiplies EF, but does not change its direction Multiplies EF, but does not change its direction

Third Class LeverThird Class Lever With a third-class lever, the effort With a third-class lever, the effort

force is applied between the force is applied between the fulcrum and the resistance force.fulcrum and the resistance force. Examples of third-class levers Examples of third-class levers

include tweezers, hammers, and include tweezers, hammers, and shovels.shovels.

A third-class lever does A third-class lever does not not change the direction of forcechange the direction of force; ; third-class levers always produce third-class levers always produce a gain in speed and distance and a gain in speed and distance and a corresponding decrease in a corresponding decrease in force. force.

EF is between fulcrum and RF (load) EF is between fulcrum and RF (load) Does not multiply force Does not multiply force

Resistance moves farther than Effort.Resistance moves farther than Effort.

Multiplies the distance the effort force travelsMultiplies the distance the effort force travels

Wheel and AxleWheel and Axle

The wheel and axle is a simple The wheel and axle is a simple machine consisting of a large machine consisting of a large wheel rigidly secured to a smaller wheel rigidly secured to a smaller wheel or shaft, called an axle. wheel or shaft, called an axle.

When either the wheel or axle When either the wheel or axle turns, the other part also turns. turns, the other part also turns. One full revolution of either part One full revolution of either part causes one full revolution of the causes one full revolution of the other part. other part.

PulleyPulley

A pulley consists of a A pulley consists of a grooved wheel that turns grooved wheel that turns freely in a frame called a freely in a frame called a block.block.

A pulley can be used to A pulley can be used to simply simply change the change the direction of a force direction of a force or to or to gain a mechanical gain a mechanical advantage, depending on advantage, depending on how the pulley is arranged. how the pulley is arranged.

PulleyPulley A pulley is said to be a A pulley is said to be a fixed fixed pulleypulley if it does not rise or fall with if it does not rise or fall with the load being moved. A fixed the load being moved. A fixed pulley changes the direction of a pulley changes the direction of a force; however, it does not create force; however, it does not create a mechanical advantage. a mechanical advantage.

A A moveable pulleymoveable pulley rises and falls rises and falls with the load that is being moved. with the load that is being moved. A single moveable pulley creates A single moveable pulley creates a mechanical advantage; a mechanical advantage; however, it does not change the however, it does not change the direction of a force. direction of a force.

The mechanical advantage of a The mechanical advantage of a moveable pulley is equal to the moveable pulley is equal to the number of ropes number of ropes that support the that support the moveable pulley. moveable pulley.

Inclined PlaneInclined Plane

An inclined plane is An inclined plane is an even sloping an even sloping surface. The inclined surface. The inclined plane makes it easier plane makes it easier to move a weight from to move a weight from a lower to higher a lower to higher elevation.elevation.

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Inclined PlaneInclined Plane The mechanical The mechanical

advantage of an advantage of an inclined plane is equal inclined plane is equal to the length of the to the length of the slope divided by the slope divided by the height of the inclined height of the inclined plane. plane.

While the inclined While the inclined plane produces a plane produces a mechanical mechanical advantage, it does so advantage, it does so by increasing the by increasing the distance through distance through which the force must which the force must move. move.

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Although it takes less force for car A to get to the top of 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.the ramp, all the cars do the same amount of work.

A B C

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Inclined Plane--examplesInclined Plane--examples 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 steep mountain passes. passes.

WedgeWedge

The wedge is a modification The wedge is a modification of the inclined plane. of the inclined plane. Wedges are used as either Wedges are used as either separating or holding separating or holding devices. 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 as wedge can be thought of as two inclined planes joined two inclined planes joined together with their sloping together with their sloping surfaces outward. surfaces outward.

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 to somewhat difficult to visualize, it may help visualize, it may help to think of the threads to think of the threads of the screw as a type of the screw as a type of circular ramp (or of circular ramp (or inclined plane). inclined plane).

MA of a screwMA of a screw

MA of an screw can be calculated by dividing the circumference of the screw (π*d) by the length between the turns in the screw (lead of screw thread)

Efficiency of MachinesEfficiency of Machines We said that the input force times the distance We said that the input force times the distance

equals the output force times distance, or:equals the output force times distance, or:Input Force x Distance = Output Force x DistanceInput Force x Distance = Output Force x DistanceHowever, some output force is lost due to friction.However, some output force is lost due to friction.

The comparison of work input to work output is The comparison of work input to work output is called called efficiencyefficiency. .

No machine has 100 percent efficiency due to No machine has 100 percent efficiency due to friction. friction.

Calculating efficiency:

Review: Simple Machines Concept Map

Compound Machines?