I'm currently taking marine science and the assignment is to build a non electric submarine that can sit on top of the water for 30seconds then dive down to the bottom or close to the bottom, and and then rise back up to the surface. This will take place in a fishtank at the school. No strings no touching or moving it no electricty Yeah I have no idea how I'm going to build it. Any ideas? I'm thinking I should start with a plastic bottle.
have you seen these? it may give you an idea on where to start. Torgo - Baking Powder Submarines & Baking Soda Submarines
Good call. Do this. Your trouble is then finding material that will float for 30 seconds before it sinks.