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Explanation of Simple Machines - Succeed in Understanding Physics. Also refer to physical science, lever, screw, pulley, ramp, energy, work, forces, friction, mechanics, Ron Kurtus, School for Champions. Copyright © Restrictions
Simple Machines
by Ron Kurtus (revised 13 October 2008)
A simple machine is a mechanical device that creates an improvement of the output force over the input with a minimum of moving parts. The improvement could be creating a mechanical advantage or changing the direction of the force. Mechanical advantage is the increase of force, distance or speed from the input value.
Around the 16th century, the classic list of simple machines was determined, consisting of the lever, wheel and axle, pully, inclined plane, wedge and screw. The wheel and axle is a form of a lever. Likewise, the wedge and screw are special applications of the inclined plane. It was once thought that all complex machines consist of a combination of these simple machines.
Questions you may have include:
- What do the lever and wheel and axle do?
- What do the inclined plane, wedge and screw do?
- What does the pulley do?
This lesson will answer those questions. There is a mini-quiz near the end of the lesson.
Lever and wheel and axle
The lever simply consists of a rod or board that pivots on a fulcrum, creating a mechanical advantage. The wheel and axle is a type of lever, using different diameter wheels to create a mechanical advantage.
Lever
The lever is a classic simple machine that achieves a mechanical advantage according to the ratio of the output or load arm of the lever divided by the input or effort arm.
Lever is a simple machine
The force mechanical advantage of a lever is:
MAf = do/di
where
- MA is the mechanical advantage
- do is the output distance from the fulcrum to the position of the load
- di is the input distance from the fulcrum to the position of the effort force
Also,
MAf = Load/Effort
This type of lever alsos change the direction of the force.
Distance or speed MA
By moving the fulcrum, you can increase the mechanical advantage for distance the load travels or for the speed of the load.
Efficiency
The efficiency of the lever is very high, since the loss due to friction at the fulcrum is low.
Wheel and axle
The wheel and axle is considered a lever of sorts. Turning the axle creates a speed or distance mechanical advantage on the outer surface of the larger wheel.
Different sized gears can also create a mechanical advantage.
Crank
You can push on the handle of a crank, and it will create a twisting force or torque on the axle. This is a variation of the wheel and axle.
Inclined plane, wedge and screw
Inclined plane
The inclined plane or ramp makes raising a weight to a given height easier, according to the angle of the incline. Unfortunately, the resistive force of friction from sliding the object on the ramp can negate the mechanical advantage.
Variations of the inclined plane are the wedge and screw.
Wedge
Although a wedge is considered a simple machine, it is really a special application of an inclined plane.
Screw
The screw is really an inclined plane that is wrapped around a shaft. It also acts like a wedge, forcing itself into a material.
Hydraulic press
Although textbooks seldom mention the hydraulic press as a simple machine, it certainly meets all the criteria.
Pulley
A major purpose of a pulley is to change the direction of the input force. You can pull down one a pulley rope, and the rope will lift the object upward.
Pulley changes direction of force
Complex set of pulleys
A complex set up pulleys, such as a block-and-tackle configuration, can result in a mechanical advantage. The question is that if it is a complex set, is it still a simple machine? Probably not.
Summary
Simple machines usually exchange using a smaller force over a greater distance to move a heavy object over a short distance. The work required is the same, but the force required is less. The are also simple machines that help to reduce the resistance of friction or such.
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Resources
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Mini-quiz to check your understanding
If you got all three correct, you are on your way to becoming a Champion in Physics. If you had problems, you had better look over the material again.
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