Is creating your own "experiment" considered cheating during a physics exam?
No, this is perfectly fine. In physics, it is common to see students making odd motions as they think through the problem or apply rules like the right hand rule. The usual caveats apply: you must not be distracting or obnoxious, must not broadcast data that other students could use to cheat, and must follow all announced regulations.

Yes, like with anything else, there are a million corner cases and caveats and unreasonable proctors that we could have fun trying to anticipate -- but I suggest we find more productive ways to spend our mental energies.