Bell ringer If the input force is bigger than the output force, then the

input distance is __________ than the output distance.

If the output force is bigger than the input force, then the input distance is __________ than the output distance.

If the input force is smaller than the output force, then the input distance is __________ than the output distance.

If the output distance is bigger than the input distance, then the input force is __________ than the output force.

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Simple Machines

Physical Science

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Types of Machines:

Simple machines are simple tools used to make work easier.

Compound machines have two or more simple machines working together to make work easier.

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Simple Machines Simple Machine Does work with one

movement... There are six simple machines:

(1) lever (2) pulley (3) inclined plane (4) wedge (5) screw (6) wheel and axle

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Lever

Lever Bar that pivots around fixed point. Fixed point = fulcrum

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Three Classes of Levers

IF F OF

1st Class Lever

F OF IF

2nd Class Lever

F IF OF

3rd Class Lever

IF = Input forceF = Fulcrum (pivot point)OF = Output force

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Three Classes of Levers 1st class lever

Change direction of force Examples: scissors, seesaw

Fulcrum is always between input force and output force in a first-class lever.

IF F OF

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Three Classes of Levers 2nd class lever

Does not change direction of force Examples: wheelbarrow, paper cutter

F OF IF

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Three Classes of Levers 3rd class lever

Examples: baseball bat, arm, golf club, tennis racket

F E R

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Mechanical Advantage and Levers 2 arms of lever:

The input arm is the distance between the input force and the fulcrum.

The output arm is the distance between the output force and the fulcrum.

If input arm > output arm, IMA > 1 If input arm = output arm, IMA = 1 If input arm < output arm, IMA < 1

Output ArmInput Arm

Mechanical Advantage and Levers

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Output Arm

Input Arm

Input Arm

Output Arm

IMA = 1

IMA < 1

IMA > 1

Which type of lever?

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Which type of lever?

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3rd Class Lever

Which type of lever?

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Which type of lever?

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2rd Class Lever

Which type of lever?

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Which type of lever?

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1rd Class Lever

Which type of lever?

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Which type of lever?

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3rd Class Lever

Which type of lever?

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Which type of lever?

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1rd Class Lever

A Crowbar Is A First-Class Lever

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A crowbar is a first-class lever. It changes the direction of the applied force. Because it has a long effort arm and a short resistance arm, it also greatly multiplies the force.

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Pulley

Pulley a chain, belt, or rope wrapped around a wheel… Can change direction or size of Force.

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Pulley Fixed pulley one that is attached to a

ceiling, wall, etc. Only changes the direction of the effort force MA of a single fixed pulley is always one.

Movable pulley pulley hung on a rope that it moves with the effort force… Can multiply the effort force, but cannot

change the direction… MA for movable pulley is always greater than

one.

A Fixed Pulley Changes

direction of force.

MA = 1 Use just as

much force to lift the box as you would by picking it up directly.

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100 lbs

100 lbs

A Moveable Pulley Does not change

direction of force.

MA = 2

Allows you to lift a 100-pound weight with only 50 pounds of force, but…

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100 lbs

50 lb

s

2 feet

1 foot

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Pulley

You can combine fixed and movable pulleys to increase the MA even more…

This is a pulley system…

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Pulley Systems

IMA = 1

IMA = 2 IMA = 4IMApulley = strands of rope that support the mass.

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Inclined Plane Inclined plane slanted surface used

to raise obj. A ramp.

IMA of ramp > 1

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Inclined Plane

Length of plane

Heig

ht

Without An Inclined Plane

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With An Inclined Plane (And Rollers)

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Force

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Wedge Wedge a V-shaped object whose

sides are two inclined planes sloped toward each other.

Examples include: knife blade razor blade axe head a door stopper

Sharpening increases AMA...

Wedges

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010

20

3040

50

60

Newtons

010

20

3040

50

60

Newtons

Compare the force needed to split a piece of wood using each axe head. Which axe head has the higher MA?

The sharper axe head has the higher Mechanical Advantage.

It takes less force to do the same amount of work.

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Screw Screw Inclined plane

wrapped around cylinder. Closer threads larger AMA...

Examples: Hardware screw Light bulb base Jar lid

Without Screws

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Lifting this gate manually is hard work; it requires lots of force.

With Screws

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Screws change rotational motion into straight-line motion. It takes a lot less force to lift the gate, but it takes a longer time.

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Wheel and Axle Wheel and axle a lever that rotates

in a circle… Made of two wheels of different sizes… Axle is a smaller wheel… Larger wheel turns about the smaller axle… Wheel moves through a greater distance; Effort force applied to the wheel is multiplied at

the axle… Examples:

Bicycles, Ferris wheels, water wheels, gears…

Wheel and Axle The wheel and axle

makes it easier to raise the crate.

Any force applied to the large wheel is multiplied in the smaller axle.

But the wheel must be turned much farther to lift the crate.

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Gears A gear is a

modified wheel and axle.

Gears can change the size or direction of a force.

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Compound Machines Compound machines

combination of two or more simple machines…

***Remember…simple or compound, you can get no more work out of a machine than you put into it!! Machines cannot multiply work!!!

An automobile engine is a compound machine made of many simple machines, including pulleys, wheels and axles, levers, and screws.