Chapter 5
Simple Machines
Types of Simple Machines
 A simple machine is a machine
that does work with only one
movement of the machine.
 There are six types of simple
machines: lever, pulley, wheel
and axle, inclined plane, screw
and wedge.
Lever
 Lever
 a bar that is free to pivot
about a fixed point, or
fulcrum
output
arm
input arm
Fulcrum
Engraving from Mechanics Magazine, London, 1824
“Give me a place to stand and I will move the Earth.”
– Archimedes
Lever
 First Class Lever


output force is always in opposite
direction to the input force
can increase force, distance, or
neither; depending on location of
fulcrum
Lever
 First Class Lever
examples: seesaw, pliers,
scissors, tongs
Lever
 Second Class Lever
 output force is always
greater than input force
Lever
 Second Class Levers
examples: wheelbarrow
(wheel is fulcrum), bottle
opener, spring diving board
Lever
 Third Class Levers
 always increases output
distance
Lever
Third Class Levers
examples: baseball bat,
broom, tweezers
Inclined Planes
 A sloping surface that reduces
the amount of force required
to do work
 Increases the distance over
which work is done, so less
force has to be applied
 Examples: ramps, zigzagged
paths, roads that go around
mountains
Pulley
 Pulley
 grooved wheel with a rope or
chain running along the
groove
Pulley
 Ideal Mechanical Advantage
 equal to the number of
supporting ropes
IMA = 0
IMA = 1
IMA = 2
Pulley
 Fixed Pulley




changes only direction
of force
does not increase
force
IMA always = 1
Distance you pull
downward = distance
weight moves upward
Pulley
 Movable Pulleys



Can multiply force
IMA = 2
The distance you pull rope upwards =
twice distance weight moves upward
Pulley
 Block & Tackle



combination of fixed & movable
pulleys
increases force (IMA = 4)
may or may not change direction
Pulley
 The block and tackle shown has
a IMA of 4.
Wheel and Axle
 Wheel and Axle

Consists of a shaft or axle
attached to the center of a
larger wheel, so that they rotate
together Wheel
Axle
Wheel and Axle
 Usually the input force is applied
to the wheel, and the output force
is exerted by the axle.
 Doorknobs, screwdrivers, and
faucet handles are examples of
wheel and axles.
 Gears- wheel and axles w/ the
wheel having teeth around its rim;
turning one gear causes the other
to turn
Screw
 Screw
 inclined plane wrapped in a
spiral around a cylinder
The Screw
 The IMA of a screw is related to
the spacing of the threads.
 The IMA is larger if the threads
are closer together. However, if
the IMA is larger, more turns of
the screw are needed to drive it
into some material.
 Examples: construction screws, jar
lids, spiral staircase
Wedge
 Wedge
 a inclined plane with 1 or 2
sloping sides
 It changes the direction of
the input force; used to split
t
things
Wedge
 Zipper

2 lower wedges push teeth together
1 upper wedge pushes teeth apart
◊
Other examples: axe, knife blade

Compound Machines
 Two or more simple machines
that operate together form a
compound machine.