From: Ronald Wong (ronwong@inreach.com)
Date: Thu Sep 09 1999 - 23:44:44 PDT
Message-Id: <l03102802b3fccd929bda@[209.209.19.200]> Date: Thu, 9 Sep 1999 23:44:44 -0700 From: Ronald Wong <ronwong@inreach.com> Subject: Re:swinging Magnets
-----------------------------
>
>Subject: Swinging Magnets
>From: "Sidney Keith" <sidkeith@hotmail.com>
>Date: Tue, 07 Sep 1999 08:10:43 PDT
Sidney Keith said:
>
>I've been showing my classes a neat toy I purchased at the Exploratorium
>store -- five magnets suspended as pendula from a rod, which swing together
>like the metal balls on desktops. When only two of the magnets are left
>attached to the rod and free to swing, pushing one begins a strange pattern
>-- one stays still while the other swings back and forth, then they change
>places -- the other one stays still. This alternation goes on until all
>motion dies down. If the two are started in time together, however, they
>continue to swing as a pair and no alternation of swing develops. The
>brochure says the alternation is an example of "coupling" between the
>magnets; how can I explain it to the students using basic concepts of
>harmonic motion, momentum and energy?
If you happen to have the Exploratorium's "Science Snackbook", you'll find
a snack called (are you ready for this?) "Coupled Resonant Pendulums". It
has a fine explanation of what is going on. The snack is another version of
what you have and is worth building if only to show your students that the
phenomena manifests itself in ways other than that which you have
demonstrated to them using the magnets. The set-up given in the snack book
is a little more complicated than necessary. Two pendulums of the same
effective length (they don't even have to be made of the same material)
hanging from the same rod clamped to a vertical support will do just fine.
The string used in the snack just makes the transfer of energy from one to
the other more apparent (less magic) and is worth doing for that reason.
What we have here is another example of the transfer of energy due to
resonance - a very common and important method of energy transfer (think of
TV, radio, vision, hearing, an object's color, a musical instrument's
sound, etc...) and is something that your students should be made aware of.
You might also want to build the "Resonator" - another snack from the Snack
Book. Include a fourth rod and ball that is identical to one of the others
and you'll have another coupled oscillator in a snack that is basically
designed to show the principle of resonance in general. A "twofer" in
otherwords. When one of the two matched pairs is set in motion only it's
identical twin will draw energy from it.
Now to the more important question: Where does the magnetic force of the
magnets come from?
ron
This archive was generated by hypermail 2b29 : Thu Oct 19 2000 - 11:09:25 PDT