The apparatus instructions provide a formula: (deflection) = [(Load)(beam
length cubed)] / [4(beam width)(beam height cubed)(Young's modulus)].
Graphing deflection vs load (for constant length) or deflection vs beam
length cubed (for constant load) should then give a straight line from which
Young's modulus is calculated as a factor of the slope.
______________________________________
Fred Lemmerhirt
Waubonsee Community College
Sugar Grove, Illinois
flemmerhirt@mail.wcc.cc.il.us <mailto:flemmerhirt@mail.wcc.cc.il.us> http://chat.wcc.cc.il.us/~flemmerh/physics.html
<http://chat.wcc.cc.il.us/~flemmerh/physics.html>
-----Original Message-----
From: brian whatcott [SMTP:inet@INTELLISYS.NET]
Sent: Friday, December 08, 2000 6:40 PM
To: PHYS-L@lists.nau.edu
Subject: Re: Trouble with "flexure of beams" apparatus
As a modest reality check, I used a commercial beam code (Archon
Beam)
to verify the relations:
a simple beam with pinned supports and a central point load
gave a linear increase in maximum deflection with load, thus:
beam 100 units long, central point load 1000 units, deflection 0.718
units
500 0.359
250 0.18
A simple beam with pinned supports and a fixed central point load of
1000
units
100 units long, deflection 0.718 as before
126 units long 1.413
144 2.145
159 2.887
This confirms the basic premise.
I conclude that the analytical derivation of modulus from slope is
in error.
I am unfamiliar with the procedure given. What is it?
brian whatcott <inet@intellisys.net> Altus OK
Eureka!