Science Buddies: "Ask an Expert"

For my science project, I am going to build a small rail gun and test different capacitors. I do not know very much about capacitors of rail guns. I am planning on using a power supply from an old model train set. The rails I intend on using are two feet long, 3/4 inch wide 1/4 inch tall. I will be accelerating two gold plated neodymium 1 inch disk magnetics attached by a metallic rod. I will be testing different capacitors to ee what changes. I need advise on what I should change on this design and what capacitors to use. Some formulas would also be nice. Any help I get would be very appreciated. Thank you.

Have you tried to research any of this on your own? http://en.wikipedia.org/wiki/Railgun has some information you might find useful. Other searches will yield other information as well.

I am using I modified version of this frame to build my rail gun. http://sci-toys.com/scitoys/scitoys/ele ... ilgun.html. Will I need to change the design of the rails more then just making them thicker? What capacitors would provide the most fun results?

I am planning on using a power supply from an old model train set.

Most train set motors that I am familiar with run on AC current. Rail Guns require DC current. If you don't understand the difference, do a little research on "Alternating Current" and "Direct Current". You can "rectify" AC current to produce DC current but doing this as part of your project might not be the best use of your time and project funds.

I do not know very much about capacitors

You should do some reading on "R-C circuits" to better understand how capacitors behave in simple circuits and how charge and voltage are related to capacitance. The project you referenced utilized batteries as a DC power source which made it a very simple circuit. To do the same thing with capacitors, you will have to come up with a way to charge them (note the plural) and you will have to figure out how much total capacitance is required to supply enough current for enough time to provide the acceleation you want. The amount of charge six 9v batteries can supply for a full second to the simple rail gun can't be stored in a single commercial grade capacitor at safe working voltages. The Wiki artical I referenced earlier has the fundamental formula that is involved in the rail gun physics.

If you want to do a great Science Fair Project, you need to take a step back and look up the Scientific method on this site and then come up with a hypothesis that you can actually test within your equipment, money, time, and math background. It doesn't have to be elaborate and complicated and involve a lot of test and support equipment to be a great project.