My high school sophomore has done a #sciencefair project that I'm actually interested in and it's kinda cool.
The effect of water temperature on laundry detergent effectiveness.
The idea is that common laundry detergents (we picked just one brand) say that they're just as effective in cold water as they are in hot. So, are they?
The science fair rules at the school prohibit brand comparisons. So we're not comparing different detergents, we have just 1. The variable is water temperature.
So my son and his partner did 2 white fabric types (cotton and polyester), 4 common stains (tomato sauce, dirt, grass, coffee) with 2 trials in hot and 2 trials in cold water. A total of 2 x 4 x 2 x 2 == 32 squares (plus 4 reference squares that never got stained, only unstained and washed).
We took photos with controlled lighting and such (to the best you can in a living room). We converted the color photos to greyscale and took an average pixel value. (This is where it gets really crude)
The idea is that the fabric starts near white (226 average pixel value). We stain it and it gets darker (e.g., 86 average pixel value). Then we wash it and it gets cleaner, and we get another pixel value (maybe 220).
So we're comparing images of washed fabric to see whether washing in hot versus washing in cold made a difference.
We are still looking at the numbers. But it's very interesting. He learned so much spreadsheets, er, I mean SCIENCE! Just the lessons of keeping all the samples straight, labeling them, being systematic about capturing data, doing math in spreadsheets. It was a great lesson.
It certainly helps to have a scientist like @steggy handy. She helped seed the idea and keep him sciencing right as he did all his samples.