How to Make a Plastic Bottle Submarine

Gouge a hole into the cap of the 20 oz bottle. It is possible to use a sharp knife, screwdriver, or nail to do this. Make sure the hole is just large enough for the flexible straw to fit into the opening.

Cut three holes on one side of the bottle. There should be a hole near the bottom of the bottle, one in the middle, and one near the top. These holes should be easier to cut than the hole in the cap.

Stack the pennies into 3 different piles. One pile should have 4 pennies, one should have 8 pennies, and the last should have 12 pennies. Keeping the piles uniformly stacked, wrap each pile in aluminum foil.

Place a rubber band directly below each hole on the 20 oz bottle (as shown above). Place the 4 penny stack under the rubber band that is closest to the top of the bottle. Place the 8 penny stack under the middle rubber band. Place the 12 penny stack under the rubber band nearest to the bottom of the bottle.

Ensure the pennies are not covering the holes you made. The should be held in place by the rubber bands beneath each hole. This side of the bottle is going to be the bottom of your submarine.

Place about 1 inch of the short end of the flexible straw into the hole in the bottle cap. Make sure the flexible part of the straw is still outside of the cap. Screw the cap onto the 20 oz bottle. Position the straw so that the long end of it is pointing upwards (remembering that the side with the pennies is the bottom). Tape the straw to the cap to ensure it stays in place.

Gently put the submarine into the water, making sure that the long end of the straw does not completely submerge and take on water. The submarine should sink a bit. Once it stops sinking, blow into the straw to watch it resurface.