CHAPTER 8 MACHINES

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CHAPTER 8MACHINES
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MACHINES

• Machines make work easier by
• changing the force you exert in
• size or direction, or both.
• But it does not change the
• amount of work done.
• A machine is a device that
• makes work easier.

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Types of Machines

• Lever
• Inclined Plane
• Pulley
• Wheel and Axle
• Wedge
• Screw

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MACHINES

• SIMPLE MACHINES
• Do work
• with one
• movement

• COMPOUND MACHINES
• Are a combination of two or more simple machines.

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MACHINES
SIMPLE MACHINES
COMPOUND MACHINE
INCLINED PLANE TYPE
LEVER TYPE
AXE

• Inclined
• Plane
• Screw
• Wedge

• Lever
• Wheel
• Axle
• Pulley

Wedge and Lever
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VARIABLES
EFFORT FORCE (Fe) is the force you exert on a
machineRESISTANCE FORCE (Fr) is the force
applied by the machine to overcome
resistance.EFFORT DISTANCE (de) is the
distance moved by the effort force.RESISTANCE
DISTANCE (dr) is the distance moved by the
resistance force.
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VARIABLES
WORK INPUT (Win) is the work put into the machine
WORK OUTPUT (Wout) is the work that the machine
puts out.
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IDEAL MACHINE
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MECHANICAL ADVANTAGE (MA) is the number of times
a machine multiplies the effort force.
IDEAL MECHANICAL ADVANTAGE (IMA)
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EFFICIENCY
An ideal machine has an efficiency of 100.
Machines have efficiency of lt 100
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• Machines make work easier by changing the force
  you exert in size and/or direction.

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LEVERS
A lever is a bar that is free to pivot, or turn,
about a fixed point. The fixed point of a lever
is called the fulcrum.
EFFORT FORCE

RESISTANCE FORCE
FULCRUM
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LEVERS
The part of the lever on which the effort force
is applied is called the effort arm. The part of
the lever that exerts the resistance force is
called the resistance arm.
EFFORT ARM

RESISTANCE ARM
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LEVERS
EFFORT ARM

RESISTANCE ARM
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FIRST CLASS LEVER
The fulcrum is always in between the effort force
and the resistance force. Examples seesaw,
hammer, hair clip, bottle opener, crow bar and
cart
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FIRST CLASS LEVER
EFFORT FORCE
EFFORT ARM
RESISTANCE ARM
RESISTANCE FORCE
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SECOND CLASS LEVER
The resistance is located between the effort
force and the fulcrum. They always multiply
effort force. Examples nutcracker,
wheelbarrow, hole puncher, bottle opener, lemon
squeezer
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SECOND CLASS LEVER
EFFORT FORCE
EFFORT ARM

RESISTANCE ARM
RESISTANCE FORCE

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THIRD CLASS LEVER
The effort is located between the resistance
force and the fulcrum. They do not multiply
effort force. Examples rake, broom, fishing
pole, your arm, and hockey stick
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THIRD CLASS LEVER
EFFORT FORCE
RESISTANCE ARM
EFFORT ARM
RESISTANCE FORCE
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THIRD CLASS LEVER
EFFORT FORCE
RESISTANCE ARM
EFFORT ARM
RESISTANCE FORCE
Effort arm is always shorter than the resistance
arm, so it cannot multiply force. Its MA
is always less than 1.
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LEVERS WITH A HUMAN TOUCH
First Class Lever
Your neck muscles support the effort force to
hold up the resistance weight of your head.
Second Class Lever
Tip of your feet-Fulcrum Weight
-Resistance Muscles- Effort
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LEVERS WITH A HUMAN TOUCH
Third Class Lever
Elbow-Fulcrum Biceps-Effort Weight-resistance
R
E
F
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PROBLEM 1
A lever uses a force of 250 N to move a rock
that weighs 3000 N. Find the mechanical
advantage of using the lever.
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PROBLEM 3
A simple machine allows a worker to move an
effort distance 45 cm in order to move a
resistance distance 20 cm. What is the ideal
mechanical advantage of the machine?
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PULLYING WITH PULLEYS
A pulley is a grooved wheel with a rope or a
chain running along the groove. A pulley works
something like a first class lever. Instead of a
bar a pulley has a rope. The axle of
the pulley acts like the fulcrum. The
two sides of the pulley are the effort
arm and the resistance arm.
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SINGLE FIXED PULLEY

• It is lifted the same distance as it is pulled
  at the other end of the rope.
• Example flagpole, blinds.
• Force is not multiplied. There is only a change
  in the direction of the force applied.

W
F
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SINGLE MOVABLE PULLEYS

• Force is multiplied.
• IMA 2, since two wires
• are supporting the
• resistance. The effort
• distance must be twice
• as large as the resistance
• distance.
• Exampleconstruction
• cranes.

F
W
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BLOCK AND TACKLE

• It is combination of fixed and movable pulley.
• It can produce large
• enough force to lift
• automobiles.

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WHEEL AND AXLE
Wheel and axle is a simple machine consisting of
two wheels of different sizes that rotate
together.
Examples doorknob, faucets, handles, steering
wheel of a car etc.
An effort force is applied to the larger wheel.
The smaller wheel, called the axle, exerts the
resistance force.
It allows us to use less force to do work.
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WHEEL AND AXLE
Gear is a modified wheel and axle machine. It is
wheel with teeth along its circumference. Effort
is exerted on one of the gears and the other gear
turns.
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INCLINED PLANE
Slanting boards and ramps are called inclined
planes. They are sloping surfaces used to raise
objects. Wweight, Hheight, Llength, Fforce
L
H
F
W
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L
H
F
W
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PROBLEM 5
What is the ideal mechanical advantage of a ramp
4 cm long and 2 cm high?
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PROBLEM 8
What is the efficiency of a machine with work
input 1000 J and work output 700 J?
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SCREWS
Screw is another form of inclined plane. The
threads form a tiny ramp that runs from its tip
to near its top. As you turn the screw, the
threads seem to pull the screw into the wood.
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SCREWS
When a screw is turned , it moves forward. At the
same time, it presses against the material
around it. Many turns are needed to move the
screw a short distance. But the screw produces a
far greater force than the force needed to turn
it.
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WEDGE
Wedge is a form of inclined plane. It is a
moving inclined plane. The material remains in
one place while the wedge moves through
it. Examples blade of an axe, knife blade, razor
blade, door stop, chisel.