If you have a school science fair coming up and are looking for a fairly simple science project, try making a submarine. You can use a soda bottle and a few other items to create your very own submersible vehicle. Since most of the required materials are common household items, this is going to be a fairly inexpensive project. Using a drinking straw or narrow plastic tube, you can also control how deep the submarine sinks during your demonstration.
Drill a hole into the bottle cap. The hole should be wide enough for the plastic tubing or straw to fit snugly. Drill three holes along the length of the bottle about 1 to 1.5 inches apart. The holes should form a line.
Make three stacks of pennies. Use four pennies for one stack, eight for the second stack and 12 for the third stack. Wrap each stack in plastic wrap.
Tape the stacks of pennies along the same line as the holes you drilled earlier. Affix the tallest stack near the hole by the bottom of the bottle, the middle stack near the centre hole and the shortest stack near the hole closest to the bottle top.
Feed the plastic tubing or straw into the bottle through the hole you made in the bottle cap. Use the tape to secure the plastic tube and create a tight seal around the hole.
Place the submarine into an aquarium or tub filled with water; the holes you drilled will let water into the submarine, causing it to sink. When you want the submarine to surface, blow into the plastic tube. The air pressure will force the water back out through the holes.