3rd Grade Science Fair

Greetings,
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.
Thanks
Stephan aka Becky's Dad
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Stephan Blackman wrote:

There might be an ASTM test method defined for preparing plaster samples for strength testing. A library might be able to obtain it for her.
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Sounds like a neat project for an eight year old!
Why not got to the US Gypsum guru, and ask your question?
http://www.gypsumsolutions.com/webQA/webQA.asp
I hope this works . . . & good luck to Becky!
Carl Sachs Composites Engineer (retired)
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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 conclusion. 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.
Prof. K

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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.
RT
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