PSN-L Email List Message

Subject: science fair seis
From: sean@...........
Date: Tue, 17 Apr 2001 17:36:00 -0500 (CDT)

Hi seismometer Mom,

I agree with Erich's comments.

I have often been a judge for the local science fair, and have seen
many versions of paper mache' volcanos (models aka "Close Encounters"
providing no science), earthquake "predictions" based on caterpillars 
(a result of selective hearsay and coincidence), and wooden seismometers 
crushed by an ever increasing mass of bricks in an attempt to get 

My usual approach to a fair exhibit is to first try to find an explicit
statement of the scientific question of the display. This is the
"how do we know ...." or "Why does" or  some hypothesis that can
be demonstrated by a simple experiment (beans grow faster in an 
electric field). If there is no question or hypothesis, there can be
no scientific test or demonstration of a principle, and therefore,
no "results".  For a seismograph or seismometer display, the question 
is "how do we detect the faint ground movement of distant earthquakes".

Then I look for some experiment to evaluate the question. Usually
the answer is known by science, so showing how we know it is 
demonstrated by some replication of the physical experiment or, 
in the case of like math or astronomy, a large poster detailing the 
logical steps that lead to the conclusion is presented (some have
that ring of verbatim Brittanica, especially when a gross error in
copying is evident).

So for the "how do we know" science display, a demonstration of the 
core physics is usually presented within the amateur limitations of
the student. For a seismometer/seismograph, recording the relative 
motion of a suspended inertial mass with respect to the moving ground 
is the key concept. Amplifying the miniscule motion (0.001mm) 
from a distant quake is more advanced. A comprehensive background
poster of earth/core wave propagation is easy to assemble. And a
poster with good graphics can detail all the concepts, including
wave propagation and quake location without having to build a 
seismograph. A demo on a map on the table of triangulation of the 
epicenter location from station S-P travel times represented by 
using marked tapes is a nice interactive display.

A fatal misconception is that some hardware something must be built
that should prove or demonstrate the point, (often overlooking the
practical alternative of borrowing a professional instrument and
then carefully labeling the key components.) This construction then 
becomes the prime effort of the display even though the student 
(parent) has not grasped the physics or science involved.  Then the 
display becomes an exhibit of the construction skills of the student 
(parent), which often blindly copy some article. 

I have seen beautiful all-wood Lehman type sensors but made with 
brass cabinet hinges and a brick for a mass with a pencil attached 
that writes on a tablet placed under the front side. The student 
got high marks because of the instructions: "slowly slide tablet 
out while shaking the table"; the principle of the inertial mass 
was proven, as was the registration of a the waveform passing with
time: ie "results". The display even noted that the table shaking
was about intensity MM-X, and referred it to a graphic about intensity.

However, often the entire point is missed and the "results" are
faked; ie."simulated". One seismometer display had a lead pipe hanging 
on a spring, with the attached pencil writing on a paper cylinder resting
on an open clock face (sort of turned by the minute hand). There was a
nice tracing of a teleseism, carefully labeled to agree with an
attached news clipping. But no current demonstration of how the
data was or could be made. (Fair judges often converge on a display
that challenges their ability to "make it work", and sometimes make
adjustments or add something that does make it work).

The value of an exhibit is proportional to the time devoted to it.
A good high school project will take about a year, with the last
half devoted to building whatever and trying to make it work. 
Then, in the case of a sensitive seismograph (with a magnification of
at least 1000,) you might have to wait a month for a significantly
large earthquake to record on it.

But I have never seen any seismograph displays involving even rudimentary
electronics (moving coil/magnet and amplifier), but this is the
midwest rather than California, and although electricity is a 
high school subject, the practical usefulness of it remains elusive.

And a final note: "quick" and "easy" have nothing to do with science.

Sean-Thomas Morrissey
St. Louis University.

PS: there is a design for a hardware store seismometer using modern
electronics that is neither quick (could be done in a devoted month)
nor easy (those darn electronics parts) described at:

stmseis.html" The STM-8 Leaf Spring Seismometer: Photos and Report
stmfigs.html" The STM-8 Seis: Figures, Schematics, Drawings
stmquakes.html" The STM-8 Seis: Recent Quakes, Data


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Larry Cochrane <cochrane@..............>