| Topic: |
Science > Physics |
| User: |
"Jethro" |
| Date: |
28 Mar 2007 10:47:45 AM |
| Object: |
Long rod question |
Hi all,
apologies if this is a numpty question, but it's been bugging me for a
while/
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
More importantly, how fast would the "information" travel ? Surely,
instinct tells me it must be "instant". In that case, does it mean
that the information has travelled faster-than light ?
The push might only be 0.1m/s ...
thanks in advance
.
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| User: "Nomen Lapetos" |
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| Title: Re: Long rod question |
28 Mar 2007 11:05:29 AM |
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"Jethro" <jethro_uk@hotmail.com> wrote in message
news:1175096865.605101.266100@p15g2000hsd.googlegroups.com...
Hi all,
apologies if this is a numpty question, but it's been bugging me for a
while/
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
More importantly, how fast would the "information" travel ? Surely,
instinct tells me it must be "instant". In that case, does it mean
that the information has travelled faster-than light ?
The push might only be 0.1m/s ...
thanks in advance
the rod would attenuate the motion by 1/2 per mile, so after millions of
miles the motion would be millions of times smaller.
Better to use fiber optics and then the speed of light inside that media is
less than free space.
Better to just use signal flags.
.
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| User: "Androcles" |
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| Title: Re: Long rod question |
28 Mar 2007 03:03:24 PM |
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"Jethro" <jethro_uk@hotmail.com> wrote in message =
news:1175096865.605101.266100@p15g2000hsd.googlegroups.com...
Hi all,
=20
apologies if this is a numpty question, but it's been bugging me for a
while/
=20
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
=20
More importantly, how fast would the "information" travel ? Surely,
instinct tells me it must be "instant". In that case, does it mean
that the information has travelled faster-than light ?
=20
The push might only be 0.1m/s ...
=20
thanks in advance
Tap it with a hammer. You'll communicate at the speed=20
of sound in [rod material].
There are no truly rigid rods in nature, what you'll find is your=20
rod is spaghetti.
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| User: "The Ghost In The Machine" |
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| Title: Re: Long rod question |
28 Mar 2007 09:42:34 PM |
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In sci.physics, Jethro
<jethro_uk@hotmail.com>
wrote
on 28 Mar 2007 08:47:45 -0700
<1175096865.605101.266100@p15g2000hsd.googlegroups.com>:
Hi all,
apologies if this is a numpty question, but it's been bugging me for a
while/
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
It would be more like a very very thin string. A human
hair might be at most 1 m or so in length (and that usually
on a very few girls with long, luscious locks down to
their waist -- a pain in the butt to wash, presumably; I
think nowadays most women want to make it at most shoulder
length) and maybe 50 microns in diameter, though the size is
apparently rather variable depending on hair type.
Scaled up, one might see a bar from here to Mars, about 75
million km long (give or take) on a good day, since on a
bad day Mars is all the way on the other side of Sol from
us, and about 3750 km in diameter, for a total volume of about
828 trillion km^3 of whatever material one makes the rod out of.
The Earth's volume is only about 1.083 trillion km^3.
More importantly, how fast would the "information" travel ? Surely,
instinct tells me it must be "instant". In that case, does it mean
that the information has travelled faster-than light ?
The push might only be 0.1m/s ...
Others have already pointed out that it would take about
25 million seconds or 9 1/2 months or so (depending on
material) for that push to show up on Mars -- as opposed to
merely sending a radio signal, which under these conditions
would take just over 4 minutes.
And that's assuming Mars sits in the same spot -- which
it won't; it will traverse about 3/8ths of its orbit,
as the Earth traverses about 3/4ths of *its* orbit, during
that 9 1/2 month interval. And then there's the issue of the
*rod's* orbit.
One would be far better off simply taking a tiny part of
the material used in constructing this rod and instead
building radiotelescopes. ;-)
thanks in advance
--
#191,
Windows Vista. Because a BSOD is just so 20th century; why not
try our new color changing variant?
--
Posted via a free Usenet account from http://www.teranews.com
.
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| User: "Uncle Al" |
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| Title: Re: Long rod question |
28 Mar 2007 01:59:06 PM |
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Jethro wrote:
Hi all,
apologies if this is a numpty question, but it's been bugging me for a
while/
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
More importantly, how fast would the "information" travel ? Surely,
instinct tells me it must be "instant". In that case, does it mean
that the information has travelled faster-than light ?
The push might only be 0.1m/s ...
Information travels at the speed of sound in a solid via compressional
or transverse waves. Shocks rapidly decay into soundspeed. A
mile/scond does not exceed 186,500 miles/second.
Hey git - is a six-inch glass rod stiff? Ever see a four-foot glass
rod from the factory? Wiggly. Relative stiffness decreases with
increasing aspect ratio. How thick were you planning to make your
"millions of miles long" rod?
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2
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| User: "Sam Wormley" |
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| Title: Re: Long rod question |
28 Mar 2007 02:11:02 PM |
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Jethro wrote:
Hi all,
apologies if this is a numpty question, but it's been bugging me for a
while/
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
More importantly, how fast would the "information" travel ?
Why doesn't sound travel at the speed of light in solids?
http://groups.google.com/group/sci.physics/browse_thread/thread/e7632ed35f4dea33/cbde26c380c7a36b?#cbde26c380c7a36b
"Acoustic Fields and Waves in Solids, Vol I & II" by B.A. Auld, 2nd edition
(February 1990), Krieger Publishing Company; ISBN: 089874783X
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| User: "PD" |
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| Title: Re: Long rod question |
28 Mar 2007 06:52:12 PM |
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On Mar 28, 10:47 am, "Jethro" <jethro...@hotmail.com> wrote:
Hi all,
apologies if this is a numpty question, but it's been bugging me for a
while/
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
More importantly, how fast would the "information" travel ? Surely,
instinct tells me
And let this be a lesson to you that your instinct is a notorious
huckster and misguided jester.
An experiment with an oscilloscope and a much shorter rod (say, a
meter or so) would show you that it is not instant at all, and in fact
one end of the rod will not know what the other end of the rod is
doing until after a time L / V where L is the length of the rod and V
is the speed of sound through the material of the rod.
Now, it's tempting to say, "Well, that's just a practical matter, due
to the squishyness of the material. If we had an infinitely stiff
material to make the rod...." And here is where a slightly deeper
understanding is required. It is inconsistent with the laws of physics
(that seem to work everywhere) that there can even be such a thing as
an infinitely stiff material. Let me re-iterate that -- not only does
an infinitely stiff material not exist as a practical happenstance,
but it is *physically impossible* for an infinitely stiff material to
exist. If you suppose it, just for the sake of supposing it, you are
implicitly abandoning some laws of physics in the process.
PD
it must be "instant". In that case, does it mean
that the information has travelled faster-than light ?
The push might only be 0.1m/s ...
thanks in advance
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| User: "Puppet_Sock" |
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| Title: Re: Long rod question |
28 Mar 2007 10:53:26 AM |
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On Mar 28, 11:47 am, "Jethro" <jethro...@hotmail.com> wrote:
Hi all,
apologies if this is a numpty question, but it's been bugging me for a
while/
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
More importantly, how fast would the "information" travel ? Surely,
instinct tells me it must be "instant". In that case, does it mean
that the information has travelled faster-than light ?
The push might only be 0.1m/s ...
thanks in advance
You do realize that the English translation of your post is
"abuse me till I bleed out of every orifice." Right?
You are asking a relativity question. These are supposed to
be swept inot sci.physics.relativity.
You are asking a question that gets asked very frequently.
Apologizing for doing it does not make it less rude.
And you should be able to think up the answer yourself
if you are able to understand the answer. Think "speed
of sound in materials."
Socks
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| User: "Randy Poe" |
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| Title: Re: Long rod question |
28 Mar 2007 10:53:56 AM |
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On Mar 28, 11:47 am, "Jethro" <jethro...@hotmail.com> wrote:
Hi all,
apologies if this is a numpty question, but it's been bugging me for a
while/
Assuming you could make a rod millions of miles long, and could
connect it to another planet, would it be possible to push/pull the
rod to communicate with the other end.
Yes.
More importantly, how fast would the "information" travel ?
At the speed of sound in the rod, which is on the order of
10 times the speed in air.
Surely,
instinct tells me it must be "instant".
Instinct may tell you that, but your instincts are wrong in this
case. The speed of sound tells how fast physical disturbances,
such as compressions, stretches, or bends, travel in a material.
Hence that is the speed that governs how soon a physical motion
of one end affects the other.
In that case, does it mean
that the information has travelled faster-than light ?
No.
The push might only be 0.1m/s ...
The near end would start traveling at this rate, and a compression
pulse would start traveling up the rod. The far end wouldn't
move for a very long time.
- Randy
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