Simple Machines and Technological Designs




Word Etymologies

The word "technology" comes from a Greek word for badger, because these animals build very fancy woven huts.

The word "machine" comes from the Greek word for to be able to. (It is related to the English word "may.")

So, this class is all about the things we build to help make us more able to do tasks.
 

A Task
Let's say you want to lift a piano onto a platform that is 3 meters off the ground, but it is too heavy to lift directly. How might you go about doing this?
The Inclined Plane
Though the piano is too heavy to lift directly onto the platform, we might use a ramp to slide it up into place.


The Lever

Another way we might approach this problem would be to use a lever to lift up one side of the piano a few inches, place something under this side, move the lever to the other side, lift that side a few inches and block it in place, and so on.  Little by little, we could raise the heavy piano.
The Pulley
A third option would be to attach a pulley to the piano, run a heavy rope from the ceiling, and through the pulley.  As a team of us pulled on the rope, the piano would rise.  We'd find we still had a very difficult task, but the force required would be half of what it was before.


All three of these simple machines help us do work.  What is going on here?
 
 

Work

When a force acts on an object and moves it some distance, we say that work is done.  Lifting, pulling, or pushing an object are all kinds of work.  Technically:

Work is force X distance.
 
 

Simple Machines

The inclined plane, the lever and the pulley all make work easier by changing the direction a force acts, and/or by changing the force and distance values in a situation.  However, you don't get something for nothing.
 
Simple machines do not change the amount of work done, but they can make work easier or more convenient.

You noticed when exploring the simple machines above that the less force you needed to do a task, the greater the distance over which you needed to apply that force.
 
 

Other Simple Machines
 
The Screw
The screw is really just an inclined plane wrapped around a shaft.  When the screw is turned on its axis, rotational motion is transformed into a back and forth motion.


The Wedge

The wedge is another modification of the inclined plane; in this instance, however, the plane is moved through something else.  When a splitting wedge is driven into a piece of wood, the downward force on the wedge is transformed into an outward force to split the wood.
The Wheel and Axle
The wheel and axle is a modification of the pulley in which the center pin (axle) is attached to the wheel.  Turning the wheel through a long distance with a weak force turns the axle through a shorter distance with a strong force.  Alternately, one can turn the axle with a strong force through a short distance and get the wheel to turn farther with a weak force.
Other Machine Elements
As you look around, you will find many devices used on machines that are related to the ones above:

Belts or chains often connect two or more wheel and axle assemblies.

Gears are wheel and axle combinations with teeth on the wheels.  When the teeth of one gear mesh with those on another, one wheel can be made to turn the other.

A worm gear is a gear that turns a screw, thus changing the direction of motion.

A crank and rod is a wheel with a rod attached.  As the wheel spins, the rod goes back and forth; or, one can push and pull the rod to make the wheel spin.

A cam is a wheel with a bump on it.  As it turns, it can periodically knock into or move something else.
 


Compound Machines

Many machines combine the effect of two or more simple machines in the same device.



Other Resources

There is an impressive array of resources on the web for teaching simple machines, many of which include pictures of simples machines in use, ways to explore simple machines with kids using inexpensive materials, etc.  Try going to the search engine google.com  and typing in "simple machines."


©2001 Jeff Goodman

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