All I remember is that it is a good one to do because:
It is easy to test
You dont need to make a mess
You can use mostly stuff from around the house
The results are clear and easy to quantify
A simple google search will easily show you a clear explanation of the results
It probably isnt a complex or fancy one, but it makes writing the SRP much easier and really, you are being marked on the way you develop the report according to the scientific method. You could probably do a more complex and intricate experiment but if you cant get it down clearly in the report you will struggle to do well. People look at the SRP as being about picking the best experiment and build the report around it. However, I looked at the SRP as being about the report and built my experiment/topic around writing the best report.
A useful life lesson for me because that pretty much sums up my approach towards work, keep it clear, simple and focus on the right outcome.
Disclaimer: As I said above, it was over 13 years ago so if there are any science tutors/teachers/experts out there please feel free to rebut what Ive said.