Simple Machines and
Mechanical Advantage
Simple Machines
Ancient people invented simple
machines that would help them overcome
resistive forces and allow them to do the
desired work against those forces.
Simple Machines
•
The six simple machines are:
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Lever
Wheel and Axle
Pulley
Inclined Plane
Wedge
Screw
Simple Machines
• A machine is a device that helps make
work easier to perform by
accomplishing one or more of the
following functions:
– transferring a force from one place to
another,
– changing the direction of a force,
– increasing the magnitude of a force, or
– increasing the distance or speed of a
force.
Mechanical Advantage
• It is useful to think about a machine in
terms of the input force (the force you
apply) and the output force (force
which is applied to the task).
• When a machine takes a small input
force and increases the magnitude of
the output force, a mechanical
advantage has been produced.
Mechanical Advantage
• Mechanical advantage is the ratio of output force
divided by input force. If the output force is bigger
than the input force, a machine has a mechanical
advantage greater than one.
• If a machine increases an input force of 10 pounds
to an output force of 100 pounds, the machine has a
mechanical advantage (MA) of 10.
• In machines that increase distance instead of force,
the MA is the ratio of the output distance and input
distance.
MA = output/input
No machine can increase
both the magnitude and the
distance of a force at the
same time.
The 6 Simple Machines
Inclined Plane
Screw
Pulley
Lever
Wedge
Wheel and Axle
Inclined Plane
Inclined Plane
• The Egyptians used simple machines to build the
pyramids. One method was to build a very long
incline out of dirt that rose upward to the top of the
pyramid very gently. The blocks of stone were
placed on large logs (another type of simple machine
- the wheel and axle) and pushed slowly up the long,
gentle inclined plane to the top of the pyramid.
Inclined Planes
• An inclined plane is a
flat surface that is
higher on one end
• Inclined planes make
the work of moving
things easier
The Lever
• A lever is a rigid bar
that rotates around a
fixed point called the
fulcrum.
• The bar may be either
straight or curved.
• In use, a lever has both
an effort (or applied)
force and a load
(resistant force).
There are 3 Classes of Levers
• Depends on the location
of 3 items:
1. Fulcrum – fixed point
on a lever
2. Effort Arm – the part
of the lever that
exerts the effort force.
3. Resistance Arm – the
part of the lever that
exerts the resistance
force.
 EA
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RA
1st Class Lever
– Changes the
direction of the force
– Multiplies effort force
– Magnifies speed and
distance
– Ex: seesaw, crowbar,
scissors
2nd Class Lever
– Multiply effort force
– Mechanical advantage
is always greater than
1.
– Ex: bottle opener,
boat oars, wheel
barrow
3rd Class Lever
– Magnifies speed and
distance
– Mechanical Advantage
always less than 1
– Ex: baseball bat, golf
club, broom, shovel
WHEEL AND AXEL
• The axle is stuck
rigidly to a large
wheel. Fan blades
are attached to the
wheel. When the
axel turns, the fan
blades spin.
Pulleys
• Pulley are wheels and
axles with a groove
around the outside
• A pulley needs a
rope, chain or belt
around the groove to
make it do work
Diagrams of Pulleys
Fixed pulley:
Movable Pulley:
A fixed pulley changes the
direction of a force;
however, it does not create
a mechanical advantage.
The mechanical advantage
of a moveable pulley is
equal to the number of
ropes that support the
moveable pulley.
COMBINED PULLEY
• The effort needed to
lift the load is less
than half the weight of
the load.
• The main
disadvantage is it
travels a very long
distance.
Mechanical Advantage
• Ratio of Output Force to Input Force
• Follows simple pattern with Ropes
and Pulley system
Rube Goldberg Machines
• Rube Goldberg machines are
examples of complex machines.
• All complex machines are made
up of combinations of simple
machines.
• Rube Goldberg machines are
usually a complicated combination
of simple machines.
• By studying the components of
Rube Goldberg machines, we
learn more about simple machines