MACHINES – UNIT 5

DEFINITION OF MACHINE

• ANY DEVICE THAT HELPS

PEOPLE DO WORK.

• IT DOES NOT CHANGE THE

AMOUNT OF WORK DONE

WORK CONSERVATION

• MACHINES DO NOT INCREASE THE

WORK YOU PUT INTO THEM. THE

WORK THAT COMES OUT OF A MACHINE CAN

NEVER BE GREATER THAN THE

WORK THAT GOES INTO THE MACHINE.

• MACHINES ALSO DON’T CHANGE THE

AMOUNT OF WORK NEEDED, SO…

HOW DO MACHINES MAKE WORK EASIER?

• BY CHANGING SIZE OF THE FORCE NEEDED

TO DO THE WORK AND THE DISTANCE OVER

WHICH THE FORCE IS APPLIED

• BY CHANGING THE DIRECTION

IN WHICH THE FORCE IS APPLIED

SO, WHY DO WE SAY THAT MACHINES MAKE

WORK “EASIER”?

THERE ARE 3

WAYS THAT A

MACHINE CAN MAKE

A TASK “EASIER”.

1. IT CAN MULTIPLY THE SIZE OF

THE INPUT FORCE, BUT DECREASE

THE DISTANCE OVER WHICH

THE FORCE MOVES

OUTPUT DISTANCE IS LESS

THAN INPUT DISTANCE

2. IT CAN MULTIPLY THE INPUT

DISTANCE, BUT DECREASE

THE SIZE OF THE FORCE.

OUTPUT DISTANCE IS MORE

THAN INPUT DISTANCE

3. IT CAN LEAVE BOTH

FORCE AND DISTANCE

UNCHANGED, BUT

CHANGE THE DIRECTION

IN WHICH THE FORCE MOVES.

IN OTHER WORDS…MOST MACHINES

MAKE WORK EASIER BY MULTIPLYING

EITHER FORCE OR DISTANCE - BUT

NEVER BOTH. NO MACHINE CAN

MULTIPLY BOTH FORCE & DISTANCE!!!

(THIS IS WORK CONSERVATION)

MECHANICAL ADVANTAGE

• THE NUMBER OF TIMES A MACHINE

MULTIPLIES

THE EFFORT FORCE• Formula = OUTPUT FORCE

___________________________________________________________

ie. pulleys INPUT FORCE

THE MECHANICAL ADVANTAGE TELLS

YOU HOW MUCH FORCE IS GAINED

BY USING THE MACHINE

• FOR INCLINED PLANES:

LENGTH OF INCLINE / HEIGHT OF

INCLINE

OR… INPUT DISTANCE / OUTPUT DISTANCE

• FOR WHEEL AND AXLES:

WHEEL RADIUS / AXLE RADIUS

OR… INPUT DISTANCE / OUTPUT DISTANCE

WHAT ABOUT OTHER MACHINES

WORK TRANSFERS ENERGY

• MACHINES TRANSFER ENERGY TO OBJECTS ON

WHICH THEY DO WORK (INCLUDING YOURSELF)

• WHAT’S THE DIFFERENCE IN WORK BETWEEN

CLIMBING A MOUNTAIN STRAIGHT

UP AND HIKING UP THE GENTLE

SLOPE ON THE SIDE?

TWO TYPES OF WORK INVOLVED IN USING A MACHINE

• WORK INPUT = THE WORK THAT

GOES INTO A MACHINE; EFFORT

FORCE EXERTED OVER DISTANCE

• WORK OUTPUT = THE WORK THAT

COMES OUT OF A MACHINE;

OUTPUT FORCE EXERTED

OVER A DISTANCE

KEY WORDS

FORCE DISTANCE WORK

INPUT FORCE INPUT DISTANCE WORK INPUT

OUTPUT FORCE OUTPUT DISTANCE WORK OUTPUT

WORK EFFICIENCY (%)

• COMPARISON OF WORK OUTPUT TO WORK INPUT

• THE CLOSER WORK OUTPUT IS TO WORK INPUT, THE

MORE EFFICIENT THE MACHINE.

• NO MACHINE IS EVER 100% EFFICIENT…WHY?

FORMULA = WORK OUTPUT -------------------------------------------------------------------------------------------------- x 100%

WORK INPUT

MACHINE EFFICIENCY PROBLEMS

• YOU DO 4000J OF WORK USING A SLEDGE HAMMER. THE SLEDGE HAMMER DOES 3000J OF WORK ON THE SPIKE. WHAT IS THE EFFICIENCY OF THE SLEDGE HAMMER?

WORK OUTPUT / WORK INPUT X 100

3000J / 4000J = .75 X 100% = 75%

• YOU DO 250J OF WORK USING AN INCLINED PLANE. THE INCLINED PLANE DOES 100J OF

WORK ON THE OBJECT. WHAT IS THE EFFICIENCY?

100J / 250J = .4 X 100 = 40%

REMEMBER…MACHINES CAN

MULTIPLY FORCE, BUT NOT WORK.

YOU CAN’T GET MORE WORK OUT OF

A MACHINE THAN YOU PUT INTO IT

EVEN IF YOU DO GET MORE FORCE

INCREASING EFFICENCY

• ONE WAY TO INCREASE EFFICIENCY

OF A MACHINE IS TO REDUCE FRICTION

• HOW CAN YOU INCREASE THE

EFFICENCY OF A BIKE?

EFFORT

• DEFINITION: THE FORCE YOU APPLY

TO THE LEVER/MACHINE.

RESISTANCE

• THE FORCE THAT YOU AND THE MACHINE

ARE WORKING AGAINST.

• ALSO REFERRED TO AS THE LOAD.

• FOR EXAMPLE, WHEN USING A WHEELBARROW

TO MOVE DIRT, THE WEIGHT OF THE DIRT IS

THE RESISTANCE.

FULCRUM

THE FIXED PIVOT POINT OF A LEVER.

Fulcrum

LEVER

LEVER

• A RIGID BAR THAT’S FREE TO MOVE ABOUT A

FIXED POINT CALLED A FULCRUM

Examples: Shovel, nutcracker, seesaw, crowbar, tweezers, fishing pole, door,

etc

THE PARTS OF THE LEVER

• WHERE IS THE FULCRUM?

• WHERE IS THE EFFORT OR FORCE?

• WHERE IS THE RESISTANCE?

THREE CLASSES OF LEVERS

• THERE ARE THREE CLASSES, OR TYPES, OF LEVERS

FIRST-CLASS

SECOND-CLASS

THIRD-CLASS

• A LEVER’S CLASS IS DETERMINED BY WHAT IS IN

THE MIDDLE: THE FULCRUM, THE RESISTANCE,

OR THE EFFORT.

FIRST CLASS LEVERS

Effort Load

• THE FULCRUM IS LOCATED BETWEEN

THE EFFORT AND THE RESISTANCE.

SECOND CLASS LEVERS

• THE RESISTANCE IS LOCATED BETWEEN

THE FULCRUM AND THE EFFORT.

THIRD CLASS LEVERS

• THE EFFORT IS BETWEEN THE RESISTANCE AND THE FULCRUM.

PLEASE TURN TO PAGE 155 IN YOUR TEXTBOOK

• FIRST-CLASS LEVER: FULCRUM IS IN THE MIDDLE.

• SECOND-CLASS LEVER: RESISTANCE IS IN THE MIDDLE.

• THIRD-CLASS LEVER: EFFORT IS IN THE MIDDLE.

WHAT CLASS OF LEVER IS THIS?

WHAT CLASS OF LEVER IS THIS?

FIRST-CLASS

SECOND-CLASS

THIRD-CLASS

X force/ distance

force / X distance

X force/ distance

How can you affect the mechanical advantage of a lever?If you move the position of the fulcrum & push down on the

lever, the box becomes easier to lift. But in order for it to become easier you have to push the lever down a great

distance of 1.5 meters to lift the box up a short distance of .5 meters at the other end of the lever. The task becomes

easier because it’s a small force but over a large distance which is converted into a large force over a short distance.

WHEEL & AXLE

• MADE UP OF TWO CIRCULAR OBJECTS OF

DIFFERENT SIZES WITH THE WHEEL AS

THE LARGER OBJECT

WHEEL & AXLE

• WHEEL IS LARGER SO IT TRAVELS A GREATER

DISTANCE. THE FORCE APPLIED TO THE WHEEL

IS MULTIPLIED WHEN IT’S TRANSFERRED TO THE

AXLE, WHICH TRAVELS A SHORTER DISTANCE.

• WHAT HAPPENS IF THE FORCE IS

APPLIED TO THE AXLE?

PULLEY

• A ROPE, BELT, OR CHAIN WRAPPED

AROUND A GROOVED WHEEL

PULLEY

• FIXED PULLEYS ONLY CHANGE THE

DIRECTION OF A FORCE

• MOVABLE PULLEYS CHANGE THE

AMOUNT OF THE FORCE

• PULLEY SYSTEMS MAY CHANGE THE DIRECTION

OF A FORCE AND THE AMOUNT OF THE FORCE

INCLINED PLANE

• A FLAT, SLANTED SURFACE

WH

•WHERE IS THE

INPUT DISTANCE?

•WHERE IS THE

OUTPUT

DISTANCE?

INCLINED PLANE

INCLINED PLANE

• MULTIPLIES THE INPUT FORCE,

AND DECREASES THE DISTANCE

OVER WHICH OUR FORCE IS

EXERTED.

WEDGE• IT’S AN INCLINED PLANE THAT MOVES

•A SMALL EFFORT FORCE IS ABLE TO

OVERCOME A LARGE RESISTANCE FORCE.

WEDGE

SCREW

• IT’S AN INCLINED PLANE WRAPPED

AROUND A CYLINDER TO FORM A SPIRAL

SCREW

• IT ROTATES & WITH EACH TURN MOVES

A CERTAIN DISTANCE.

• IT MULTIPLIES THE EFFORT FORCE BY ACTING

THROUGH A LONG DISTANCE.

MECHANICAL ADVANTAGE OF SIMPLE MACHINES

Formula = OUTPUT FORCE ___________________________________________________________

INPUT FORCE

IF A MACHINE DECREASES THE FORCE YOU USE YOU USE

TO DO WORK, YOU CAN FIND THE “IDEAL”

MECHANICAL ADVANTAGE WITHOUT KNOWING THE

INPUT AND OUTPUT FORCES. BUT, YOU MUST ASSUME

THE SIMPLE MACHINE IS 100% EFFICIENT

WH

•TO FIND THE IDEAL MECHANICAL ADVANTAGE YOU DIVIDE:

LENGTH OF THE INCLINE--------------------------------------

HEIGHT OF THE INCLINE

l IMA = ------ h

IMA - INCLINED PLANE

WH

•TO FIND THE IDEAL MECHANICAL ADVANTAGE YOU DIVIDE:

RADIUS OF THE INPUT--------------------------------------

RADIUS OF THE 0UTPUT

R (in)

IMA = ---------- R (out)

IMA – WHEEL & AXLE

WH

•TO FIND THE IDEAL MECHANICAL ADVANTAGE YOU DIVIDE:

DISTANCE FROM THE INPUT FORCE TO THE FULCRUM-----------------------------------------------------------------------------DISTANCE FROM THE OUTPUT FORCE TO THE FULCRUM

d (in)

IMA = ---------- d (out)

IMA – LEVERS

COMPOUND MACHINE

• A COMBINATION OF TWO OR

MORE SIMPLE MACHINES

GEARS

CONNECT TWO

OR MORE WHEEL

AND AXLES

TOGETHER BY

USING TEETH

GEARS

• TWO GEARS THE SAME SIZE AND NUMBER OF

TEETH WILL TURN THE SAME SPEED,

BUT OPPOSITE DIRECTIONS

• A THIRD GEAR CAN BE ADDED TO MAKE THEM

MOVE IN THE SAME DIRECTION

GEARS

• THE GEAR THAT TURNS ANOTHER GEAR

EXERTS THE INPUT FORCE

• THE GEAR THAT IS TURNED EXERTS

THE OUTPUT FORCE

GEARS

• A DIFFERENCE IN SPEED BETWEEN

TWO GEARS (CAUSED BY A

DIFFERENCE IN SIZE AND DISTANCE

EACH TURNS THROUGH)

PRODUCES A CHANGE IN FORCE

MECHANICAL ADVANTAGE OF COMPOUND MACHINES

• THE M.A. OF A COMPOUND MACHINE IS

EQUAL TO THE

SUM OF THE M.A. OF ALL

THE SIMPLE MACHINES THAT

MAKE UP THE COMPUND MACHINE

COMPOUND MACHINES

• WHAT ARE EXAMPLES OF COMPUND MACHINES YOU USE?