My eight year old daughter is trying to do a science fair project on
how will varying the amount of water used in preparing a plaster of
paris slab effect it's load bearing strength. Now that;'s a mouth full
for a 3rd grader. But in actuality the project is simple. Once is
unmolds the slabs she's going to see how much wieght they can support
before breaking. My problem is reference materials. Not too many tomes
are written on material science on a elemenatry level. Her teacher is
being a hard ass. Since the project is original there is no template
to work off from a book like 1001 amazing science fair project. I mean
we have been doing those since the fifties.
So what do I need, If their are any material scientists out there who
could help an adorable 8 year old girl in her quest to smash things
real good, I would appreciate hearing from you. I mean how could a
teacher say an expert in the field isn't as good as a book.
aka Becky's Dad
Sounds like a neat project for an eight year old!
Why not got to the US Gypsum guru, and ask your question?
I hope this works . . . & good luck to Becky!
Composites Engineer (retired)
IF that teacher had a proper college degree, it would have learned an expert
is better than any book. Books are frequently wrong, and as you found,
there are often no references for many circumstances. That is why science
is based on experimental evidence that tests a hypothesis. No textbook is
needed to establish the definition of proper science. Your daughter's
planned project is actually applied science since the mechanism is not being
investigated, but the performance of the material. So, to be accurate, a
hypothesis is needed like ' excess water makes the plaster weaker'. Then
the experiments prove it or not. To request a reference substance is again
working to an engineering (applied science) test because a comparison is
being made. The new hypothesis for science would be 'is properly made
plaster stronger than properly made pasta' , for example. Similarly asking,
which is stronger? is verified experimentally under strict conditions such
as equal cross section. Drywall is commercial plaster. Make test specimens
the same size as a hunk of drywall and look up its strength or get it from
the gypsum people like already suggested. This compares plaster to plaster.
I have judged science fairs before and one major criterion is that the
scientific method was followed and that the steps were all considered and
completed (reported and in a notebook). Rather than worry about following a
script (so to speak) as you want to do, just ensure the scientific method
was properly addressed. This can be easy or hard depending on the hypothesis
you select. Ramifications of inappropriate wording can be damaging
regardless of the amount of time spent doing the tests. It is tempting to
do experiments and then wrap them into a package that appears to meet the
criteria after the fact; but this is not following the method. Ensure the
experiment conditions capture the range of variables established by the
hypothesis. Then carry them out and report the results. What kind of
plaster might be made with 90% water? Could there be a product (test sample)
that can be tested after the excess water is evaporated in a few days?
Because the soup created will never harden in 20 minutes, doesn't mean it
must be excluded from the test matrix since the hypothesis didn't state the
condition of hardening in 20 minutes. So, now you feel you must add that
additional criterion? Yes, and so it continues until the hypothesis is 'cast
in stone' and the tests will be reported with respect to the hypothesis and
proper conclusions obtained. That something didn't work is not a proper
Now that you see science fair projects are not trivial or simplistic,
encourage your daughter to develop an appropriate hypothesis for her age and
not be over extended. I am pleased to see another science student applying
their desire for smashing things in a positive and constructive way through
a science fair project. Now, after all I wrote above, I can relate my
youthful mistake regarding a science project. The scientific method was
obvious to me when I read it in school, but I was naive then. What the
method actually meant was not so obvious and that was the harder process,
because of the details. Those things that were clear to me and obvious in
my head, were the very things that were neglected when it was time to show
what my work was. After building something neat and getting it to work and
creating a title for it, I though I was done and proud of my effort. But I
was not done. This was just a small part of what was expected of me. There
was no hypothesis nor any set of experiments defined to test the hypothesis.
There were no observations nor results and therefore no science. I knew a
lot of science by wrote and memory, but until then, never applied the method
properly. I did not get a good grade and learned a powerful lesson.
If you can't get access to professional type test equipment, I would suggest
you consider a simple beam test where the slab is supported near both ends and
load is applied at the center. A simple support fixture could be made from
wood and a force guage or spring scale could be used for loading. Experiment
with the length of the beam span until you get into a reasonable level of force
for your loading device.
Technically this would be called a three point flexural strength test.
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