Simple machines and efficiency
Types of machines
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Gears
Inclined Plane
Lever
Pulley
Screw
Simple Machine
Wedge
Wheel and Axle
A machine is a device
that is used
To make a job easier. In
other words,
the device allows you to
use less force
to complete a task.
Inclined plane
• An inclined plane is a sloping surface, such as
a ramp. An inclined plane can be used to alter
the effort and distance involved in doing
work, such as lifting loads. The trade-off is
that an object must be moved a longer
distance than if it was lifted straight up, but
less force is needed.
Examples: Staircase, Ramp, Bottom of a Bath
Tub
Inclined plane
Lever
•
A lever is a straight rod or board that pivots
on a point known as a fulcrum. The fulcrum
can be moved depending on the weight of the
object to be lifted or the force you wish to
exert. Pushing down on one end of a lever
results in the upward motion of the opposite
end of the fulcrum.
Examples : Door on Hinges, Seesaw, Hammer,
Bottle openers
Levers
Bicycle brakes
Door handle
Levers are classified according to
classes
Pulley
•
A wheel that usually has a groove around the
outside edge. This groove is for a rope or belt
to move around the pulley. Pulling down on
the rope can lift an object attached to the
rope. Work is made easier because pulling
down on the rope is made easier due to
gravity.
Examples: Flag Pole, Crane, Mini-Blinds
Pulleys
Mechanical Advantage
People use pulley systems to get a benefit called Mechanical advantage. They do
not have to apply as much force to get the same amount of work done on an object.
To determine MA of a pulley system, count the number of strings minus the
one you are pulling down on.
Pulleys
What is the MA of the system
Above?
Pulleys
Screw
A modified inclined plane wrapped around
a shaft or cylinder. This inclined plane
allows the screw to move itself or to move
an object or material surrounding it when
rotated.
Examples: Bolt, Spiral Staircase Simple
Screw
Wedge
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Two inclined planes joined
back to back. Wedges are
used to split things.
Examples: Axe, Zipper, Knife,
wood maul
Wedge
Wheel and Axle
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A wheel and axle has a larger wheel (or
wheels) connected by a smaller cylinder
(axle) and is fastened to the wheel so
that they turn together. When the axle is
turned, the wheel moves a greater
distance than the axle, but less force is
needed to move it. The axle moves a
shorter distance, but it takes greater
force to move it.
Examples: Door Knob, Wagon, Toy Car ,
Ferris wheel
Wheel and Axle
Gears
Two toothed wheels fit together either
directly or through a chain or belt so one
wheel will turn the other. Some gears may
have a screw or a toothed shaft in place of
one of the wheels. A gear may also be a
combination of toothed wheels that produces
a certain speed (such as a bicycle's top gear
which makes the bike go fast, and the low
gear for slow speed.)
Examples: Clock, Automobile, Drill
Gears
Compound Machines
• These are combinations of several
simples machines joined to form a
particular task.
Compound Machine
Compound Machines
Calculating Mechanical Advantage
MA= Force out
Force input
MA= de distance of the effort
dr distance of the resistance
dr refers to how far the object moves
de refers to how much you have to move or how
much rope that you pull in for a pulley system
Example
• Using a pulley system a boy pulls on a rope
with 10N of force and lifts a 50 N weight.
What is the MA of the pulley system?
• MA= F out/ F in or 50N/10N
• MA = 5
• There are no units for mechanical advantage.
The higher the MA, the better the machine.
Example
• A girl pulls a rope attached to a pulley system
a distance of 10 m to move a weight up 2
meters. What is the MA?
• De=10m
• Dr=2m
• MA= de/dr 10m/2m=5
Efficiency
Machines are rated
according to
efficiency. No
machine is 100
percent efficient
because of friction.
Efficiency Terms
• Force of resistance = fr( usually the weight of
the object)
• Force of effort=fe ( how much force you put
in)
• Distance of the resistance=dr (how far the
object moves)
• Distance of the effort= de ( how far you move
or how much rope you pull in from a pulley
system)
Efficiency Formulas
• (Work output/ work input) X 100
• Work Out X 100
• Work in
• Fr X dr = fe X de
Ideal MA
• The ideal mechanical advantage (IMA), or theoretical
mechanical advantage, is the mechanical advantage of an
ideal machine. It is calculated using physics principles because
no ideal machine actually exists.
• The IMA of a machine can be found with the following
formula:
• IMA = de/dr
• DE equals the 'effort distance' (for a lever, the distance from
the fulcrum to where the effort is applied) DR equals the
resistance distance (for a lever, the distance from the fulcrum
to where the resistance is encountered
• Additional websites
http://library.thinkquest.org/CR0210120/Mechanical%20Adva
ntage.html
http://www.youtube.com/watch?v=yfAdmRJDKIc
• http://atlantis.coe.uh.edu/archive/science/sci
ence_lessons/scienceles1/finalhome.htm