[Chris Ince Jr]

Chris Ince Jr  asked the Naked Scientists:
   
Let me say first of all that I love the show, and to be honest I don't know how I would survive my ten hour shifts without it. It is extremely informative and always gives me food for thought to pass the time.

My question is one that has been bothering me for some time. Let me start out with a little bit of a disclaimer: as a former US Navy nuclear reactor technician, I have had extensive education in the physical sciences, however most of it was highly specialized and, seeing as how I've hardly had to use that kind of knowledge in years, I seem to be losing it. That being said, I apologize beforehand if my question is very basic or just downright absurd.
 
Anyway, as far as I know, there has not been anything discovered that is equal to or faster than the speed of light (barring discoveries in quantum tunneling, but I'll leave that for another question).

As we know, of course, the speed of light is 186,000 miles per second. My question relates to a theory I've had dealing with mechanical energy.

I know that an experiment to test this theory is likely impossible with current technology, and even if it is, most likely impractical, but my theory is as follows:

Say that you had a very large, complex system of gears, stretching a total of 186,000 miles (obviously, the distance light travels in one second).

This would likely depend heavily on the size and arrangement of the gears, but if one large gear, placed at the start of the system, was turned, would the gear at the very end of the system, 186,000 miles away, turn instantly, making the propogation of the mechanical energy faster than or equal to the speed of light? Or would the energy simply dissipate before it even reached from the first gear in the system to the least?

That is my general question. I would also like to know if any questions or research similar to this have ever been posed and, if so, if any useful discoveries or scientific insights have come out of it.

Thanks for your time, guys. Once again, I absolutely love the show, and please keep up the good work!
 
Sincerely,
 
Christopher William Ince Jr

What do you think?

[Bored chemist]

The information would travel through the set of gears at roughly the speed of sound in the metal they were made from. It's not instant.

[LeeE]

In practice, I believe that the friction, not only of the gear bearings, but also between the teeth of the gears would absorb most of the input energy.

On top of that, you'd also have to overcome the inertia of the gear train.

Finally, as BC says, the speed of sound in the material that the gears are made from would limit how quickly the energy could be transmitted, meaning that the transmission would have to be slower than 'c' anyway.  A simpler system than a train of gears, and one that makes it easier to explain, would be a simple beam/shaft/rod.  When you deliver an impulse to one end of the beam you're momentarily compressing it, which is basically what a sound wave is, and the rate at which that compression wave travels down the length of the shaft is limited by the speed of sound of the material of the beam.

[techmind]

Finally, as BC says, the speed of sound in the material that the gears are made from would limit how quickly the energy could be transmitted, meaning that the transmission would have to be slower than 'c' anyway.  A simpler system than a train of gears, and one that makes it easier to explain, would be a simple beam/shaft/rod.  When you deliver an impulse to one end of the beam you're momentarily compressing it, which is basically what a sound wave is, and the rate at which that compression wave travels down the length of the shaft is limited by the speed of sound of the material of the beam.

Exactly what I would have said.

[Bored chemist]

You could get round the issue of friction by having a "train" of gears with just two cogs in it (or even just one, but that's hardly a system).

[Stefanb]

And wouldn't the proximity to the speed of light increase the mass of the gear infinitely so no matter how much force was applied the gear would never reach C?

[Fozzie]

Not only that, the force required to turn the first gear wheel would break the whole machine!