How do I build a submarine in which i change the mass or volume to make it float, then sink, then float?

Question

I was given a science experiment in science class. It needs to look like a submarine. and i can't have any direct contact with the sub. It needs to start floating then sink all the way to the bottom. then it needs to float back up to the top. I can't do it by using alkaseltzer like i've seen online i have to change the mass or volume of it to make it work.

Answer 1

The one solution coming out of my mind is:
Use a container which would float on water when empty but which would sink when full.
To sink, pump in enough amount of water making the container heavy thus sinking in the water.
To float, pump out the water at a pressure higher than the outside water pressure.

Answer 2

Here's one not too smart idea: Two plastic bottles tied together with a soluble link, such as a rubber band with a sugar cube link. (You can cut the rubber band, tie loops at each end of the resulting strip, and slip them over each end of the sugar cube.) Bottle 1 is empty and closed and floats when alone. When nearly full of water, bottle 2 needs to be heavy enough to sink bottle 1 when they are tied together; but the rig should float when empty. Add weight to bottle 2 as needed make this happen, and use a bigger bottle if necessary. Make smallish holes in bottle 2 where needed to allow it to fill slowly (and air to escape) when afloat, so when the rig is put in water it initially floats but then sinks. Later, when the soluble link breaks, bottle 1 floats free. It will take trial and error to adjust things so the rig works reliably and with good timing.

Answer 3

A Cartesian diver is an excellent choice. This isn't just a school project - oceanographic robots based on the principle are important tools for studying the world ocean. If the Wiki or SIO articles don't give you enough info, try Google - several experiments listed.

Answer 4

http://www.webcom.com/sknkwrks/submarin.htm