hmm... I've seen prompts like these and sometimes there's just no way around using qualitative levels for the IV. there shouldn't be any points taken off for having a bar graph since the rubric calls for "appropriate type of graph used", though you'd probably lose points in the "IV operationally defined" criterion.So I just came across an experiment, and have had similar ones in the past, using 4 different types of materials where the topic is absorbency. We had limited measuring devices: only the stopwatch and ruler we can use in competitions. My initial thoughts were doing something like porosity vs amount of water absorbed, or density vs amount of water absorbed. However there would be no way to measure porosity and density with the experiment given, so I would do something for the IV like: low density, medium density, and high density, and the experiment would use a bar graph. Is this even allowed since we couldn’t measure density and only used qualititative observations to determine this? Also what would the SOC be? Any ideas on this, and also for a better experiment idea with this topic?
I personally wouldn't use density or porosity as independent variables since they're more difficult to estimate qualitatively. it might be more suitable to use thickness of the material or just use one material altogether and simply vary its area/size quantitatively.
my teammates and I usually refer to the extreme minimum IV level when it doesn't make any logical sense to have a SOC of 0, otherwise we just use a zero level. reasoning is usually something along the lines of it being a baseline level to compare with future levels that are manipulated, so in your case, I'd go with the lowest density material.
as for other experiment ideas:
> time taken a single drop of water to absorb into different materials. time is probably more easy to measure in these types of experiments since measuring the amount of water absorbed can be difficult when the water makes a huge blob :^)
> something relating to length/surface area of the material and time to absorb completely? this one might be a stretch for relating to absorbency but on the plus side both the IV and DV would be able to be measured quantitatively.