Submarines demonstrate the concept of buoyancy. Buoyancy is the force that determines whether an object floats or sink. Submarines can do both by allowing water to enter into the sub to sink and then filling the same tanks with air to help the submarine rise to the surface. Using just a few household materials, a water bottle can be made into a submarine to help demonstrate these principles.
Cut a hole in the cap of the water bottle to allow the straw to fit inside. Use a sharp knife or a nail to make the hole in the cap.
Cut two holes into the body of the water bottle. Both holes should be located on the same side of the bottle, in a line, bottom to top.
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Create two groups of quarters, one group of four and the other group of three. Tightly wrap the quarters in aluminum foil.
Attach the quarters to the body of the water bottle using rubber bands. The group of four quarters should be located next to the hole closest to the bottom. The group of three quarters is located nearest the top. Do not cover the holes with the quarters.
Attach the lid to the bottle and slide in the short end of the flexible straw. Do not push the flexible portion of the straw into the lid. Seal the lid with tape or clay so water does not enter the bottle from this point.
Lower the submarine gently into a container of water. The holes will allow water into the sub and the quarters will help pull the sub down. Keep the long end of the straw above the surface of the water. Blow into the straw to make the submarine rise from the depths.