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To B.C.
When I had read your explanation, I found it perfectly OK. At least I could not have given a more clear and consise argument for the speed difference in T- and L-wave. I've nothing essential to add, and in the class, I would give the same explanation as yours.
Moses Fayngold,
NJIT
--- On Sun, 2/28/10, Bernard Cleyet <bernardcleyet@redshift.com> wrote:
From: Bernard Cleyet <bernardcleyet@redshift.com>
Subject: [Phys-l] Disapointed. Was: Re: different types of waves have different speeds
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Date: Sunday, February 28, 2010, 8:51 PM
I'm quite disappointed no one has replied to my request quoted below.
bc
On 2010, Feb 26, , at 13:34, Bernard Cleyet wrote:
A HS teacher on a HS list asked, "Would a Transverse Wave and a Longitudinal Wave in the same material have the same speed?"
One respondent replied, "So the answer is that different types of waves have different speeds because they are caused by slightly different phenomena."
And nothing more except two examples; one below, the other is a tuning fork.
I wish to reply with a brief description appealing to simple notions for the benefit of an unusually inquisitive student.
The respondent gave, as an example, L and T waves in an aluminum rod, à la Paul Doherty at the Exploratorium.
ringing _Al_rod
My thought is to write: (mechanical) waves require inertia and a restoring force similar to mechanical oscillators, e.g. pendulum and spring) In the L. (compression) case the inertia is the mass of the material and the restoring force the elasticity of the material characterized by the uniaxial strain/ stress in a homogenous solid (Young's modulus). OTOH, for the T. wave the inertia is the moment of inertia of an element of the bar's length and the restoring force the reaction (shear elasticity) to the shear force. Thus the T wave is very different from the L. wave.
I solicit an improved version.
bc
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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l