Yes, the speed of each disk. Yes, the control could be a disk of a specific diameter. For example, three disks could be used, and the one with the medium diameter could be arbitrarily decided upon as a standard. Yes, controlled variables are such things as the height and surface of the testing ramp, and the materials the disks are made of. V. Data Data is the only way that a judge has to determine whether or not you did an experiment.
Judges like to see tables, charts, or graphs of the measured results.
Any project that has data generally gets an automatic second look by judges. If there is no data, judges start to look for the reason why, and they usually conclude that the student doesn't understand what an experiment is or how to do one. Once you have decided on your project question, your hypothesis, and basically how you are going to test your hypothesis experimentally and record data, then start your project by designing the experiment step by step. Do perform the experiment four or more times, recording the results of each test and averaging the results. Guide to the Best Science Fair Projects.