Science Buddies: "Ask an Expert"

Hi...I did the project called "Using Super Strong Magnets to Make a Simple Motor." I found that the battery spun the fastest with two magnets attached to the bottom. I am wondering why that is? I am thinking it has to do with the weight of the magnets? What are your thoughts on that?

Thanks so much

Hello and welcome to the forums.

I just looked at the experiment (I've never built this type of motor.) How many magnets did you try - did you try from 2 to 5 as suggested? Any you found that 3 worked best (1 on top, 2 on the bottom)? 1, 3 or 4 on the bottom caused it to spin slower than 2 on the bottom?

Did you repeat the trials several times? I'm concerned that with the large amount of current involved that the battery will run down very quickly and change the results.

If after several trials, you get the same results, let us know. If so, you have discovered an interesting property of the real world - sometimes the best approach is not the theoretical best one due to real world factors. In this case you have friction (both air and the magnets). Also, you have to take into consideration the mass of the magnets. Newton's 2nd law, F = m A can be used here. (The equations in the experiment talk about the force from the magnets and current through them, can you look at both of these forces?)

You probably noticed that I did not answer your question directly. That's for you to do so that you can understand what's happening when you talk to the science fair judges.

Best of luck, and let us know what you find out!
Keith