Seesaw?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by rousejohnny</i>
<br />If there were a giant seesaw with a length greater that 1Ly and super man pushed on it, would the other end move instantaniously or would it take a year to move?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Pushing on any "rigid" object initiates a pressure wave through the object traveling at the speed of sound. Nothing happens at the far end until the pressure wave gets there. -|Tom|-

That doesn't "sound" right, but I am sure you are, it would be easy enough to test. So the object would actually bend and rebound along the rigid object at the speed of sound? So I actually can bend a rod of solid titanium even if just for a second.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by rousejohnny</i>
<br />That doesn't "sound" right, but I am sure you are, it would be easy enough to test. So the object would actually bend and rebound along the rigid object at the speed of sound? So I actually can bend a rod of solid titanium even if just for a second.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">It is curious that this "doesn't sound right" to you, but maybe it just needs to be explained better.

Every effect must have a proximate (in contact) cause that precedes it. An effect without a cause is a form of magic, forbidden as an explanation of physics. So when you push one end of a "rigid" rod, what causes the other end to move? The atoms on the surface at the far end must be pushed by their neighboring atoms one layer in. Those must be pushed by their neighbors two layers in. And so on back to the near end, which is pushed by an external force.

So we do have a string of cause and effect. It is just a question of how quickly the "push" messages are propagated along the length of the rigid rod. And the answer to that is the speed of sound in the rod. (Note: not its speed in air). So when we call something a "rigid rod", we mean that it appears rigid to our eyes because the speed of sound is so fast we can't see any delay visually in the response of the far end.

But to propose that there is no delay, and the far end reacted instantly, would be to propose "instantaneous action at a distance", a form of magic. In physics, this is the equivalent of saying "God did it", which is an excuse for abandoning the search for a physical explanation. -|Tom|-

So I guess my experiment with pulling a 1000 meter fishing line and expecting a 3 second delay would not yeild the proper results. What is the speed of sound through solid objects, I am sure it varies. The problem I have is that these solids are chemically bonded creating a bridge, could this bridge of distance not alleviate this problem?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by rousejohnny</i>
<br />So I guess my experiment with pulling a 1000 meter fishing line and expecting a 3 second delay would not yeild the proper results. What is the speed of sound through solid objects, I am sure it varies.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">It does indeed vary widely with the type of material, but is generally much faster than the speed of sound in air because air is a very inefficient transmitter of sound waves.

Don't you instinctively sense that your 1000 meter fishing line would have some natural elasticity when you pull on it suddenly? Just because it is not as elastic as a rubber band does not mean that the elasticity does not exist.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The problem I have is that these solids are chemically bonded creating a bridge, could this bridge of distance not alleviate this problem?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">It is a principle of physics and of logic that no kind of action can occur at a distance without something propagating over that distance at some finite speed. In the cases in question, the push or pull creates a pressure wave that travels along the body affecting atoms one by one. To an observer, this just means that every body is made of tiny parts, and these parts are always slightly elastic, even if the amounts are too small or too fast to see by eye. -|Tom|-

Forget the seesaw for a second, I like the fishing line idea better. Sound waves generally have varying degrees of amplitude and frequency. When such a wave travels through anything it is slowed by vectoring factors as it collides with the mass it is traveling through. The speed of travel through the fishing is dependent not only of the medium but also the characteristics of the wave. So, if there was a straight pull on the fishing line, the speed of travel should exceed that of the typical sound wave. Or, am I missing something?