Floats

How do I build a working model submarine that floats AND sinks?

For science class, I have to build a model submarine that floats, sinks, floats, sinks, and floats. Does anybody know how to do this SCIENTIFICALLY and not using a pill. I'm asking for a step-by-step procedure, and I need it by Thursday. Thanks!

Public Comments

here is a clue just remember that if your "submarine" has a volume of say 500c.c it will float quite happily until its weight increases to over 500 grams.if it weighs say 450 grams it means you will need an extra 50 odd grams to make it sink.real subs take in and expel water (i think) in order to do this so you will have to have enough empty space on your craft to take that extra weight(like a tank or 'conning tower')in the case above you would need a tank (which is already included in the 450 gram weight of floating vessel) just big enough to take on 50+ grams of water.so you would need a tank just a little bigger than 50c.c.then of course you need a way to get rid of that water to make the sub float again it doesnt have to be water but it must weigh more than 50 grams in this case hope this gives you a few ideas!
What you want to build is called a Cartesian Diver. Search the web for examples using a 2 liter bottle. By compressing the sealed bottle, you compress the air bubble that supports the "sub" and it drops.