Simple Machines
What is a Simple Machine?
• A simple machine is a device that helps to accomplish
a task by redirecting or alleviating some of the work
input required.
• Simple machines cannot create energy. They can only
redistribute or produce force on an object.
• The six basic simple machines are the lever, the
inclined plane, the wedge, the screw, the wheel, and
the pulley.
• Simple machines help people lift or move heavy
objects, split thick solids, and secure things together.
Levers
• Lever: a long piece of wood, metal,
etc. that rests on a turning point
(fulcrum) to lift or open something
• An object (load) is placed on one end,
while a force pushes the other end
down to move the object.
• Force applied x Distance (between
force and fulcrum) = Load x Distance
(between load and fulcrum)
• Examples: bottle openers, scissors,
hammers (when pulling a nail out)
Applied force 
 Lesser force (load)
Lever Types
• First Class Lever
– Fulcrum is between force input and load.
– Input (effort) and load forces are on opposite
sides, but act in the same direction.
– The closer the fulcrum is to the load, the less
effort is needed.
– Examples: see-saws, pliers, scissors
• Second Class Lever
– Load is between force and fulcrum.
– Effort and load forces are on the same side of
the fulcrum but act in opposite directions.
– The closer the load is to the fulcrum, the less
effort is needed.
– Examples: staplers, nutcrackers
More Lever Types
• Third Class Lever
– Force is between fulcrum and load.
– Effort and load forces are on the same
side, but act in opposite directions.
– Effort required to lift the load is
greater than the load.
– Examples: fishing rods, tongs, brooms
• For first and second class levers: large
output of force is gained over a small
distance (force multiplier)
• For third class levers: small output of
force is gained over a large distance
(speed or distance multiplier)
Pulleys
• A pulley is a wheel and axle
over which a rope or chain is
pulled in order to lift or lower
heavy objects.
• Pulleys change the direction
of motion/force applied to lift
an object.
• The amount of force required
to move the object remains
the same
• Using a pulley feels easier
because you are working with
gravity by pulling down on the
rope, as opposed to working
against it by pulling the object
straight up.
< Without the use of a pulley, the
required lifting force is 100lbs.
With the use of a
pulley, the required
lifting force is still
100lbs. >
Multiple Pulleys
• Force required when
using more than one
pulley to pull up an
object is less than force
required when using one
pulley to pull up the
same object.
• This is because the
weight of an object is
split by the number of
pulleys you use.
• However, the distance of
the rope multiplies by
the number of pulleys
you use also.
Two pulleys: force required is cut in half,
rope length is increased.
Inclined Planes
• An inclined plane is a surface set at an angle against the horizontal.
• Inclined planes split gravitational force in two:
– Force parallel to plane
– Force perpendicular to plane
• Only parallel force must be counteracted when moving objects up a plane
• Force required to do work is less than when pushing on a flat surface
• Mechanical advantage = slope/length of plane
• Used as ramps or sloping roads, and can be combined to form a wedge
Wedges
• Wedges consist of a pair of inclined planes set against each other.
• By moving the planes relative to each other, a wedge builds up force
in a direction perpendicular to the moving wedge.
• Mechanical advantage = slope/thickness; The advantage gained
requires corresponding increase in distance
• Wedges are used to separate or hold objects.
• Door stops, axes, and teeth are examples of commonly used wedges.
Wedge used to hold a door
Wedge used to separate an object
Wheel and Axle
• A wheel and axle is a simple machine
made up of two circular objects of
different sizes rotating on the same axis.
– The wheel has the larger diameter,
and turns about the smaller axle.
• Because a wheel is basically a lever that
can turn 360o, effort or resistance force
can be applied anywhere on that surface.
The central point of the wheel and axle
serves as the fulcrum.
• A force applied to the wheel is multiplied
when it is transferred to the axle, which
travels a shorter distance than the wheel.
– Since the wheel is larger than the axle,
it always moves through a greater
distance than the axle.
Use of the wheel and axle
• The mechanical advantage (the number
of times a machine multiplies the effort
force) depends on the radius of the
wheel and of the axle.
• The wheel allows objects to roll along
the ground, decreasing surface friction
by substituting rolling friction for
sliding friction.
• The wheel can also be used to lift
objects by wrapping a cord attached to
a weight to the axle. It is less efficient
than the lever at lifting objects.
• Examples: screwdrivers, doorknobs,
windmills, gears, Ferris wheels
Screws
• A screw is another type of an inclined plane. It is a helical
inclined plane wrapped around a cylinder to form a spiral,
with a wedge at its tip.
• The main use of a screw is to hold objects together with its
helical grooves.
• A screw can convert a rotational force to a linear force and
linear force to rotational force.
Use of Screws
• The screw’s ratio of threading determines its
mechanical advantage.
–
–
Screws with wide grooves are harder to turn,
yet travel a shorter distance to their
destination.
Screws with narrow grooves are easy to turn,
but have to be twisted over a greater spiral
distance.
• One example of the screw as a simple
machine is Archimedes’ Screw - used to bring
water up from low sources to the location of
use by passing through a helix.
• Other examples of screws include bottle
caps, worm gears, drills, wrenches, jacks,
and light bulbs.
Simple and Compound Machines
• A compound machine is composed of multiple simple machines
working together to redirect or apply force.
• While a simple machine has only one motion, complex machines
may have two or more.
• Examples of compound machines are a wheelbarrow, which uses a
lever and a wheel and axle to redirect pushing force, and a
bicycle, which redirects force from the user’s feet through pulleys
to turn the wheels and propel the user forward.
Works Cited
• http://www.uark.edu/depts/aeedhp/agscience/simpmach.ht
m
• http://www.enchantedlearning.com/physics/machines/Levers
.shtml
• http://www.simplemachines.info/netscape.htm
• http://www.howstuffworks.com/pulley.htm?printable=1
• http://www.sciencebyjones.com/simple_machines.htm
• http://www.usoe.k12.ut.us/curr/science/sciber00/8th/machi
nes/sciber/intro.htm
• http://www.mos.org/sln/Leonardo/InventorsToolbox.html