Physical Science 9 - Rio Hondo Prep s/Chapter 9.2.pdf · 1007 Chapter 9.2 3 Physical Science 9 Simple Machines There are six basic types of machines of which all other machines are

1007 Chapter 9.2 1

Physical

Science 9 Simple Machines

1007 Chapter 9.2 2

1007 Chapter 9.2 3

Physical


There are six basic types of machines of

which all other machines are composed.

Levers

Pulleys

Wheel & Axle

Inclined Plane

Wedge

Screw

1007 Chapter 9.2 4

Physical

Science 9 Simple Maachines

Levers

All levers have a rigid arm that turns around

a point called the fulcrum.

Force is transferred from one part of the

arm to the other.

The original force can be multiplied or re-

directed to help you do work.

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Force can be multiplied

using a lever. This factor

is called the

MECHANICAL

ADVANTAGE

To calculate the mechanical advantage of the

lever, you need to know two things…

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Science 9 Levers …the length of the two “arms” of the lever.

The “resistance arm” is the

length of the lever from the

fulcrum to the end of the load.

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Physical

Science 9 Levers …the length of the two “arms” of the lever.

The “effort arm” is the

length of the lever from the

fulcrum to the end of the effort.

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Physical

Science 9 Levers Mechanical Advantage

6m

Effort arm

Resistance arm

2m

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6m

Effort arm

Resistance arm

2m

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6m

Effort arm

Resistance arm

2m

This means that any

force on the effort arm

will be multiplied by 3.

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Science 9 Levers

6m

2m

As with all machines,

the amount of work

that is done is

constant (remember

W=Fd).

With this lever,

your force is

multiplied by 3,

but your

distance is only

1/3 of the effort

distance.

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Physical

Science 9 Levers

You may push the

lever down 3m, but

the weight will only be

lifted 1m.

3m down

Only 1m up

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Physical

Science 9 Levers

You may push the

lever down 3m, but

the weight will only be

lifted 1m.

3m down

Force of 3N

W=Fd=3N*3m=9Nm

Only 1m up

Fd=9N*1m=9Nm

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Physical


6m

Effort arm

Resistance arm

2m

If the weight of the block

is 30N, how much force

would you need

to lift it?

30N

?

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Physical


Effort arm Resistance arm

30N 10N

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A man could lift the Earth with

a long enough lever (and

assuming he had a place to

put the fulcrum and assuming

gravity was constant).

The Earth has a mass of about 6 x 1024 kg. If

the man had a mass of 50kg, and if the

resistance arm was 1m in length…

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Physical






gravity was constant).

…then the effort arm would have to be 1.2 x

1023 km, or 13 million light years (the center of

our galaxy is about 100,00 light years).

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gravity was constant.

At that distance, if you were to push down on

the lever at 1m/sec, it would take a million

million years to raise the Earth 1cm.

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gravity was constant.

Levers can multiply your force, but there is a

distance penalty. The higher the MA, the less

the object will move.

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What is the mechanical advantage of this

lever?

22m 6.2m

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What is the mechanical advanage of this

lever?

22m 6.2m

3.5

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22m 6.2m

3.5

If the man has

a mass of

61kg, how

much mass

can he lift with

this lever?

210kg

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Physical


3.5

If the man

lowers the

lever by 3m,

how far will

the load be

raised up?

210kg

.9m

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Physical


3.5

The Force is

multiplied by

3.5, but the

distance is

divided by 3.5.

210kg

.9m

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Physical


3.5

Remember,

simple

machines do

not reduce the

amount of

work that is

done!

210kg

.9m

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Physical


How much

would you

have to weigh

to lift this

3,400N

elephant? Effort arm = 42m

Resistance Arm = 3.0m

First, calculate the

MA of this lever…

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Physical


How much

would you

have to weigh

to lift this

3,400N

elephant? Effort arm = 42m


First, calculate the

MA of this lever…

MA=14

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Physical


How much

would you

have to weigh

to lift this

3,400N

elephant?


Since your force is

multiplied by 14,

divide the weight of

the elephant by 14.

You must weigh…

240N

(or 54 lbs).

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Science 9 Levers

Examples of 1st Class Levers

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Physical

Science 9 Levers


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Physical

Science 9 Levers


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Science 9 Levers


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Science 9 Levers Levers can also be used in reverse to

increase the distance per time…As in a

catapult.

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Physical

Science 9 Levers Levers can also be used in reverse to

increase the distance per time…As in a

catapult.

Why do you think they

call it a “cat”apult?

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Physical

Science 9 Levers

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Physical

Science 9 Levers

2nd Class Levers

Fulcrum (pivot

point) is at the

end of the lever.

Load is in the

middle.

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Science 9 Levers

2nd Class Levers

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Physical

Science 9 Levers

2nd Class Levers

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Physical

Science 9 Levers

3rd Class Levers

Fulcrum (pivot

point) is at the

end of the lever.

Applied force is

in the middle

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Physical

Science 9 Levers

3rd Class Levers

Third class levers generally multiply distance

instead of force.

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Physical

Science 9 Pulleys

Pulleys are modified

levers. The “fulcrum”

is the middle of the

pulley.

The rest of the pulley

behaves like the

“rigid arm” of a lever.

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Physical

Science 9 Pulleys

A simple pulley

merely re-directs the

force.

It’s mechanical

advantage is 1.

(100N in, 100N out)

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Physical

Science 9 Pulleys

A multiple pulley

system can have

a mechanical

advantage of

more than 1.

This system has a

MA of 4 (four

pulleys).

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Physical

Science 9 Pulleys

Multiple pulley

systems are

called “block

and tackle”

pulley systems.

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Physical

Science 9 Pulleys

As with all simple

machines, pulleys

can multiply the

force, however

the amount of

work that is done

remains the

same.

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Physical

Science 9 Pulleys

In this system

(used in cranes),

the distance the

weight is lifted is

split between the

4 lengths of wire.

So for every 4

meters of

movement here,

the weight is only

lifted 1 meter.

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Physical

Science 9 Pulleys

1 Fixed

Pulley

MA = 1

2 Pulleys

MA = 2

3 Pulleys

MA = 3

4 Pulleys

MA = 4

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Physical

Science 9 Pulleys

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Physical

Science 9 Pulleys

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Physical

Science 9 Wheel & Axle

A Wheel & Axle is a pulley and/or a

lever connected to a shaft.

Lever Pulley (wheel)

Connecting

Shaft

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Physical

Science 9 Inclined Plane

Inclined planes are like ramps and

other sloped routes.

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As with every simple

machine, the amount of

work that is done is the

same – it takes less

force to go up this

road, but you have to

travel a longer distance

to get where you are

going.

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The Mechanical

Advantage of an

inclined plane is…

Height

LengthMA

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If you have a road that

is 25km in length, and

goes up 5km, the

mechanical advantage

of the road is 5.

Height

LengthMA

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This ramp

multiplies

your force,

but you’ll

have to push

it farther to

get to the top!

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Physical


How many

simple

machines are

in this

picture?

Inclined Plane

Wheel & Axle

1st Class Lever 3rd Class Levers (at least 6)

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Science 9 Wedge

A wedge is two inclined planes placed back

to back.

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Physical

Science 9 Wedge

A wedge concentrates a force into a small

area, making it useful for cutting things.

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Science 9 Wedge



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Science 9 Wedge



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Science 9 Screw

An inclined plane wrapped around a cylinder.

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Science 9 Screw


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Physical

Science 9 Screw


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Physical


Review: The six simple machines are…

Levers

Pulleys

Wheel & Axle

Inclined Plane

Wedge

Screw

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It’s time to play…

I’ll display the device, you tell

me what simple machine it

is…

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1st Class Lever

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Physical


Pulley

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1st class lever

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Physical


Wedge

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Physical


Wheel & Axle

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Inclined Plane

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Physical


Pulley (Block & Tackle)

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Physical


3rd Class Lever

(resistance/effort/fulcrum)

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Physical

Science 9 Compound Machines

A compound machine is a machine that

uses two or more simple machines.

2 levers, each with a

wedge (for cutting), and a

screw (which acts as a

fulcrum for the levers).

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Physical

Science 9 Compound Machines

A compound machine is a machine that

uses two or more simple machines.

A bicycle has numerous

simple machines.

1007 Chapter 9.2 82

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Physical Science 9 - Rio Hondo Prep s/Chapter 9.2.pdf · 1007 Chapter 9.2 3 Physical Science 9 Simple Machines There are six basic types of machines of which all other machines are