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Physics/Science Fair Project


Dear Dr. Nelson,

I am a 7th grade homeschooler doing a science fair project for the Washington State Science and Engineering Fair. I am testing to see if vitamins or gases (nitrogen or CO2) can decrease the toxicity of acid to baker's yeast. I am wondering what is the best way to measure how active the yeast cells in each sample are, which would indicate how many were alive and well. My original thought was to place the yeast in a bottle and put a balloon over the top, and then measure the circumference of the balloon to see how much CO2 the yeast produce. If this is an accurate way to determine yeast cell activity, then this would work for me; if not, I would like to know an accurate way to do this. Another AllExperts expert mentioned to someone else (that did a yeast project) that a hydrometer is a good way to measure the sugar content of a sugar water medium and then use that to determine the activity level of the yeast cells. This sounds like a good way to do it, but my project uses a viscous mixture of flour, sugar, and water as the yeast medium, and I do not know if the hydrometer would still be accurate in this case. I would greatly appreciate it if you could take the time to provide some insight on this.



Well, this is a biology question and not a physics question, really.  I might refer you to my friend Dr. Trista since she's both an expert in biology and a great brewer.  A hygrometer will tell you how much mass has been converted to CO2 accurately, so one is appropriate.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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