Physics Question: Are Eyeglasses Mechanical?

Jeff Stallard · Post by **Jeff Stallard** » Tue Jul 19, 2005 7:57 am

The definition of a machine is a device that transmits or modifies energy to perform or assist in the performance of tasks. The difference between a tool and a machine is that the machine is fairly independent. A lens takes light input, modifies it, then transmits it into our eyes in such a way that assists the performance of our eyes. Furthermore, they are very nearly independent (youput them on, but that's it).

So what do you say: are glasses a mechanical device? I think so, but a friend doesn't agree. I just want to see what others think.

Tyler · Post by **Tyler** » Tue Jul 19, 2005 7:59 am

So.....
if we are combining machines with our bodies, are we becoming cyborgs????

missy · Post by **missy** » Tue Jul 19, 2005 7:59 am

I paid to have Lasik, so I don't worry about it!
(I'm a chemist, not a physicist)......

GaryKelly · Post by **GaryKelly** » Tue Jul 19, 2005 8:02 am

Nay, say I. A machine, in terms of physics, is a device which performs work, and lenses don't perform work.

amar · Post by **amar** » Tue Jul 19, 2005 8:04 am

tricky question, is a machine then not also something that must have moving parts for it to function? Well, www.webster.com doesn't say so, but still, I can't think of any machine without moving parts.
A lense also does not actively do anything at all, whereas machines, as i understand the meaning of that word, do...hmm..

I.D.10-t · Post by **I.D.10-t** » Tue Jul 19, 2005 8:12 am

Machines belong to classical Neuton physics; light was conceived differently back then and would not have fallen under the same concept of work as movement of things.

Interesting question, I would say no.

But that is speculation, not fact.

PS all you need is

you can derive everything else.

Jeff Stallard · Post by **Jeff Stallard** » Tue Jul 19, 2005 8:12 am

A lens DOES do something. It alters the vector of light energy. It doesn't have to have cogs, chains, and bearings to be a machine. Anything that modifies energy to assist in the performance of tasks is a machine.

Doug_Tipple · Post by **Doug_Tipple** » Tue Jul 19, 2005 8:16 am

Are eyeglasses mechanical? Speaking as someone who has spent five years working in an optical lab, my best answer is that it depends on your definition of mechanical. Change your definition slightly and you have a different answer.

Eyeglasses are more than just lenses, they also have mechanical properties such as hinges, springs, etc. Unfortunately, the screws on my glasses keep coming unscrewed and getting lost. Then I have to go around with a paper clip hinge pin until I can get another screw the right size. I finally put a drop of superglue on the screws, and I haven't lost a screw since then.

I would say that anything that you have to work on with a screwdriver and a pair of pliers has mechanical aspects.

Martin Milner · Post by **Martin Milner** » Tue Jul 19, 2005 8:16 am

amar wrote:tricky question, is a machine then not also something that must have moving parts for it to function? Well, www.webster.com doesn't say so, but still, I can't think of any machine without moving parts.
A lense also does not actively do anything at all, whereas machines, as i understand the meaning of that word, do...hmm..

How about an electro-plating machine? Unless you count the electrons as moving.

Jeff Stallard · Post by **Jeff Stallard** » Tue Jul 19, 2005 8:17 am

I.D.10-t wrote:Machines belong to classical Neuton physics; light was conceived differently back then and would not have fallen under the same concept of work as movement of things.

Classical Neutonian physics deals heavily with vector forces, which is exactly what a lens deals with.

jbarter · Post by **jbarter** » Tue Jul 19, 2005 8:18 am

I'm useless with machines and I wear glasses for reading. They can't be a machine or I'd mess them up somehow. QED.

Jeff Stallard · Post by **Jeff Stallard** » Tue Jul 19, 2005 8:20 am

Doug_Tipple wrote:Eyeglasses are more than just lenses, they also have mechanical properties such as hinges, springs, etc.

That's a good point; glasses are more than just the lenses. However, the difference between a machine and a tool is that a machine must operate fairly independently. A hammer modifies energy to assist in the performance of tasks, but because it is not independent, it is not a machine. Are eyeglass frames independent? Hmm...not sure.

GaryKelly · Post by **GaryKelly** » Tue Jul 19, 2005 8:25 am

I refer you to my previous answer, and expand upon it by suggestion that a lens doesn't modify energy. Even if the lens were completely lossless, then energy in=energy out, and therefore no modification has occured at all.

Amar, a crowbar has no moving parts, but since it operates on the principle of a lever, it can be classified as a machine (since it performs work).

GaryKelly · Post by **GaryKelly** » Tue Jul 19, 2005 8:29 am

Oh and I offer this:

http://www.britannica.com/ebc/article?t ... achine&ct=

which I submit is a more appropriate definition of 'machine' than the one found on the likes of hyperdictionary.com

Jeff Stallard · Post by **Jeff Stallard** » Tue Jul 19, 2005 8:30 am

GaryKelly wrote:I refer you to my previous answer, and expand upon it by suggestion that a lens doesn't modify energy. Even if the lens were completely lossless, then energy in=energy out, and therefore no modification has occured at all.

Not quite. The light's vector has been modified. Furthermore, to get nitpicky, the speed of the input light was modified temporarily while it passed through the glass.