Science Buddies: "Ask an Expert"

My daughter has done her research as well as her experiment for her 5th grade science fair project on geothermal energy - The Power of Heat is Right Under Your Feet! She conducted these with adult supervision on her own, but I must say I was surprised as to the result of the number of pinwheel rotations. She conducted several experiments (1 center hole, 9 holes around edge of foil with 1 center hole and 20 holes around edge of foil with 1 center hole) at a height of 6 inches and 8 inches both with and without the can. My surprise was that the number of rotations of the pinwheel decreased from the 1 center hole to the 9+1 hole experiment, but then increased with the 20+1 hole experiment. Does that sound right - number starts, goes down and then back up? I would have assumed that the pinwheel rotations would constantly increase with the number of holes increasing, not go from 10 rotations, to 7 rotations up to 17 rotations (all without a can at 6 inches). And then with a can at 6 inches from 7 rotations, 2 rotations and 6 rotations. And was also surprised that the number of rotations with the can experiment were less than without the can.

Do these results make sense? Any feedback would be much appreciated. I'm trying very hard to let her do as much of this on her own and don't want to discourage her by stepping in to "redo" the results. Thank you for any assistance you can provide!!!

epicquad4,

Thank you for your question. The best part of science is when you get a counter-intuitive result. However, these are the most difficult to defend because you must show rigorous attention to all the variables and show repeatability. In your case, how many times did she repeat the experiment? If she did less that 3 runs of all cases then results could be held suspect. Also, there are some control variables, such as the level of water, heat setting on stove, temp of water, placement of pinwheel over heat source, timing of experiment, etc...

Remember, there are no wrong answers in science. There are only the observed results for the given test conditions. Our job is to document those results, the conditions they were taken under, and what we could do to refine those results. If the results are accurate, I would say it has something to do with how the steam diffused out of the holes but it is hard to say without seeing what the test setup looked like.