I am designing an experiment in which a plastic coke bottle will be made to float, subsurface, sink, and return to the water's surface by external manipulation. (depth of 1 meter) The way I want to do this is using three syringes and fish-tank tubing to control the volume(s) of air in the plastic bottle. In addition, I will need to add weight to the bottle to keep it sturdy, and take into account maybe a ballast tank type design incorporated. The overall aim of this is to measure the acceleration of the bottle coming up (what i'll measure), compare to what it should be, using the appropriate equations. Since constructing this plastic bottle submarine is a big part of what I am doing, I am wondering if there is a better method of controlling the volume of air other than syringes. My other question is whether it would be wiser to use a small bottle (1L or 2L) or a large bottle (3L or 4L) and what might be some of the pros and cons of each. Thanks in advance.