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Path: utzoo!watmath!clyde!bonnie!emh
From: emh@bonnie.UUCP (Edward M. Hummel)
Newsgroups: net.physics
Subject: Re: "speed of light" puzzle
Message-ID: <489@bonnie.UUCP>
Date: Sun, 26-May-85 17:52:13 EDT
Article-I.D.: bonnie.489
Posted: Sun May 26 17:52:13 1985
Date-Received: Mon, 27-May-85 00:39:41 EDT
References: <1720@ut-ngp.UUCP> <578@lll-crg.ARPA>, <136@heurikon.UUCP> <471@hou2g.UUCP>
Organization: AT&T Bell Laboratories, Whippany NJ
Lines: 22


>> Consider the point of intersection of the blades of a scissors.
>> Picture a BIG scissors -  mile long blades.  As you close the
>> scissors, the point of intersection could move faster than the
>> speed of light even though the blades are moving "slowly".
>This isn't true.  The blades of the scissors are held together
>by E&M forces between the atoms.  When the handle is squeezed,
>the E&M force won't be transmitted to the far end of the blades
>any faster than C.  The result is that the blades will "bend".
>The point of intersection of the blades will propigate no faster
>the "bend" - the speed of light.

Sorry, Jim, but it is true.  The propagation of "motion" along a
rigid body is indeed limited by the "forces between the atoms".
A push on one end of an object takes a while to propagate to the
other end of the object (the speed of sound gives a first order
estimate).  But once the motion has been obtained the point of
intersection of a large pair of scissors indeed can travel faster
than c.

Ed Hummel
...!ihnp4!clyde!bonnie!emh