Speed of signaling in a rigid rod?

Good question...but an actual rod 100km long would require a huge force to move it and would compress significantly so the signalling rate wouldn't be as quick as appears at first glance. Also the data rate would be abysmal!

Del

I'm not sure, but I seem to remember reading about simple mechanical computers (made a long time ago) that used rigid rods to transfer information (or maybe they used gears).

What about using pnuematic lines instead of rigid rods to transfer the compression waves?

The CR4 dictionary doesn't recognize the word "pnuematic". How odd.

To 1st question:

because of its compliance the waves are damped as amplitude very fast, internal friction is a second argument against and last but not least same compliance leads to a low velocity so that time delay becomes unacceptable if frequencies are important

To your remark:

as far as I know the right orthography is "pneumatics", it is at least what I met in different books but english (american) not being may language I may be wrong.

You could hit the end of the rod to send a compression wave, or make it osscilate (like twanging a violin). To send a clear signal down the rod, you'd have to hit it very square on the end.

I clipped this for you;

**********************

The propagation speeds of traveling waves are characteristic of the media in which they travel and are generally not dependent upon the other wave characteristics such as frequency, period, and amplitude. The speed of sound in air and other gases, liquids, and solids is predictable from their density and elastic properties of the media (bulk modulus). In a volume medium the wave speed takes the general form

This relationship works fairly well for water with tabulated values:

This agrees well with the measured speed of sound in water, 1482 m/s at 20°C. The situation with solids is considerably more complicated, with different wave speeds in different directions, in different kinds of geometries, and differences between transverse and longitudinal waves.

For example, a general tabulated value for the bulk modulus of steel gives a sound speed for structural steel of

Comparing to one tabulated example for stainless steel shows wide variation between the speed for longitudinal and transverse waves, with this calculated value somewhere in between.

*****************

I think it sounds 'unpossible' in real terms. String telephones are much more fun

For longitudinal waves the Young Modulus should be considered and with its value of around 2 E 11 the result is near to the tabulated sound velocities.

This is a commonly asked question (probably due to the large number of very long rigid rods left over from the Whiskey Rebellion). NASA has a site which addresses this and similar ideas

http://helios.gsfc.nasa.gov/qa_gp_sl.html#speedlight

Hello virudh:

is this something you want to impliment or, just a thought?

You would have to hit it pretty hard.

Hello babybear,

You would have to hit it pretty hard

Or have a microphone, amplifier and some discrimination filters.

Hello virudh,

But if you go to that much work a piece of copper wire or an optical fiber would be more cost effective. By the time you buy the steel and support, weld the pieces together, deal with corrosion, and set up your signaling system.

Also you would want to have some system for dealing with lightning, static electricity, etc.

One thought though is to make your supports an A brace with a small triangle as the top of the A. Use a chain slung from each side of the bottom of the triangle as a sling to suspend the rod in. that should minimize the absorption of the compression wave energy by the mounts.

Brad

Hello U V:

I know it is a hypothetical question, but, never the less, it is a bit odd?

I know short 'push-rods' work over say at most several metres, but to even think to propose it for such a long distance is silly. My opinion and no offence to anyone.

Very true,

I look at it like this to be mechanically effective it will need to be at least an inch in diameter to not just bow side ways. A 2 inch pipe would be better. The mass of a 100Km 5cm steel pipe is a lot to move to transmit data, even using gravity to return the mass.

I suppose you could cause a harmonic standing wave and play with that to transmit data but what a can of worms that would be.

Better yet polish the inside, pull a vacuum on it, and pulse a light or laser down it. Use different wavelengths to multiplex.

Brad

You certainly can transmit data through the length of a solid rod using an acoustic transmitter and a receiver at the far end. Transmitters and receivers are often magnetostrictive or piezoelectric. Prpogation can be extension, transverse, or torsion. Propogation velocity is different for the different modes. This is essentially how an acoustic delay line works.

If we are going to play around with a 100km long steel rod then we need to take into account the coefficient of linea expansion. From memory 6.6 x 10^-6 / degree F. If you have a big temperature you have a big problem.

BAB

You are correct. In applications where constant delay time is critical, low exapansion, or constant modulus alloys are used. In applications where transmission time is not critical, expansion properties can be ignored.

The only rigid rod equation I can recall from my school days is one my father, also an engineer, taught me. He claimed that the angle of the dangle was inversely proportional to the heat of the meat. I think he may have been correct. More research is clearly needed....

Hello Guest,

there is so much inuendo flowting about here! And what you said is pretty much what I would if I was brave enough...............

Take care

why don't just use the rod as an electrical conductor... measure its impedance, and transmit an electrical signal down it... pick your signal parameters and any protocols necessary?............. mountain out of a mole hill???? or better yet... wireless system???