Re: moving wall laser demo

[Physics <Physics@ROCHESTER.RR.COM>]

----- Original Message -----
From: "Herbert H Gottlieb" <herbgottlieb@JUNO.COM>
> However, I doubt if the demonstration would work with
> thick stone, or reinforced concrete, walls.

We do a "bend the wall" demo on our stone walls.  We attached the end of a
long metal rod to the wall with some clay.  at the other end we have a small
mirror attached to a pin and set the pin under the rod as if you were doing
an expansion of metal experiment.  When a laser is shining on the mirror and
the wall is even slightly pressed within a couple of meters of the rod, you
can get a major deflection.  The setup amplifies the movement very well and
can get the laser dot to travel across a few meters.

A humorous story about this occurred one day while teaching this and the dot
was moving very strangely by itself.  Of course the students asked why it
was doing this.  I was stymied until I walked out of the room into the next
room where I found one of my colleagues pushing on the wall from the other
side!  He thought this was hysterical...

Just more proof that demos don't always work the way you plan...

Gene Gordon
Fairport High School