Can anyone give me some science fair ideas that can be tested? Planning on using a Rasberry pi 3 for the project, but I don't know any good ideas. The question should be like, "How does [input] affect [output]?"
Ummm... For a science fair, you are usually expected to come up with your own ideas. If you can't, a chat with a suitable teacher is probably in order. However, don't expect people here to do your homework for you.