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I agree - mostly.  

On one hand, I think people may sometimes get caught up with these arbitrary designations.  Having been trained in physics, I really have thought of all machines as the same type - ones that play with exchanging the factors involved in work ( w= f d).  A wheel is a series of levers (all with equal length arms) - so is a pulley - let's be honest - pulleys *are* wheels (and they normally have axles).

On the other hand, these simple machine paradigms seem to make it easier for people without a full understanding to see relationships between different devices.  Thus many people like the idea of all machines being variants of 2 - 5 different devices.  One thing to remember is that these classifications were created by us to help us categorize things and put them away in nice little boxes in our minds - but they are our categorizations (nature rarely categorizes things as cleanly as we do (hmmm...this may be a controversial statement - we shall see)).  Thus for those who like classifying items, and who don't think of items in terms of trading off force for distance and or directional changes (what all simple machines do), then maybe the prior categorizations help people with a base level of understanding.

For me, I will still think of all simple machines as being devices that allow you to change the direction and amount of force, only by spreading the work across a distance (often with a small loss of energy).

-William


  
On May 12, 2011, at 10:39 AM, Jason Jay Stevens wrote:

> ISEN-ASTC-L is a service of the Association of Science-Technology Centers
> Incorporated, a worldwide network of science museums and related institutions.
> *****************************************************************************
> 
> I think society is ripe for an overhaul of the simple machine dogma.  That's just a proposal, btw, I don't have any satisfying ideas for replacements yet, myself.
> 
> My pa is an engineer, and I remember him telling me that there are only TWO kinds of machines: a lever and an inclined plane.  Everything else is a derivation:  a wheel pivots around an axle the same way a lever pivots around a fulcrum; a screw--as has been mentioned--is a helical inclined plane.
> 
> It's brilliant and beautiful, but a classification like that doesn't serve any function except maybe in vector visualization exercises.  Does it?
> 
> Is a pendulum really just a lever? Is a leaf spring really an inclined plane? Does that help me design or fix anything?  (Maybe kinda sorta intuitively in a way, but...not really...)
> 
> The paradigm is definitely a great way to get budding lil engineers to think about machines, though.  It worked for me, even if it aroused lifelong suspicions.
> 
> btw, I (who am only one and not many visitors, admittedly) would look at the zipline and call that simple machine that rides the cable a "wheel."  It clearly does the same job a wheel typically performs, ergo.  If a label called that a pulley, I might knit my brow and scratch my head.  If it called it a special kind of lever, I'd call my dad up and tell him with pride that he's still my go-to guy for engineering.
> 
> : j
> Jason Jay Stevens
> interactive museum exhibition design
> Flutter & Wow
> www.flutterwow.com
> 
> 536 Roosevelt Avenue
> San Antonio, Texas 78210
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William Katzman
Program Leader
LIGO Science Education Center
"Inspiring Science"
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