I need some magnet wire for a school project, it will be wrapped around a ~5cm nail and powered by either a 9v or a couple AA batteries. It won't be doing any heavy lifting or anything, just some small metal balls. What AWG wire gauge should I buy? What voltage should I run off that AWG wire (I am aware that wrapping more wire causes a higher resistance and a higher power draw)?
The only real limitations are how much power you can pull from your supply and how quickly the electromagnet heats up (remember it's a glorified heater as well as a magnet). The strength of the magnet is dependent on both the number of turns and the current (Ampere-turns). 1 turn at 10A has roughly the same magnetic strength as 10 turns at 1A. The difference is more turns means more resistance which will try and limit the current so you then need more voltage to push more current through the coil. If you've got lots of wire try a few combinations (be a good demo to have two magnets which lift the same weights yet have visibly different numbers of turns, a 9V battery powering a high turn count, low current magnet and some AAs in parallel powering a low turn count, high current magnet - that'd really confuse your audience)