Key words: Simple Machines, physical science, lever, screw, pulley, ramp, energy, work, forces, friction, mechanics, Ron Kurtus, School for Champions. Copyright © Restrictions

Simple Machines

by Ron Kurtus (revised 29 October 2015)

A simple machine is a mechanical device that consists of a minimum of moving parts but yet can create an improvement of the output over the input. The improvement could be creating a mechanical advantage or simply changing the direction of the output. 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. The list consisted of the lever, wheel and axle, pulley, inclined plane, wedge, and screw.

These simple machines can be broken into three classifications: lever simple machines, rotating simple machines, and inclined plane simple machines.

Questions you may have include:

• What do lever simple machines do?
• What do rotating simple machines do?
• What do inclined plane simple machines do?

This lesson will answer those questions. Useful tool: Units Conversion

Lever simple machines

The lever simply consists of a rod or board that pivots on a fulcrum, creating a mechanical advantage or a change in direction.

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,

This type of lever also changes the direction of the force.

By moving the location of the fulcrum, you can increase the mechanical advantage for distance the load travels or for the speed of the load.

The efficiency of the lever is very high, since the loss due to friction at the fulcrum is low.

Rotating simple machines

Rotating simple machines include rollers, wheel and axle, crank, and pulley.

Rollers

The wheel or roller by itself can make it easier to move objects by overcoming friction.

Wheel and axle

When an axle is added to a wheel, a torque on the axle increases the speed of the outer surface of the wheel. Likewise, turning the wheel from its outer edge increases the force applied from the axle.

Crank

A crank is like a wheel and axle.

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.

Pulley

A pulley is a wheel and axle, that uses a rope to lift objects. 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.

Inclined plane simple machines

Variations of an inclined plane include a ramp, wedge, and screw.

Ramp

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. Turning the shaft around its central axis transforms rotational motion and torque into axial motion and force.

A screw can also act like a wedge, forcing itself into a softer material.

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.

Resources and references

Ron Kurtus' Credentials

Websites

Machines Resources

Books

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.

Students and researchers

www.school-for-champions.com/machines/simple_machines.htm

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