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Home-made submarine
Science at Home


      Straw (5 cm).
      Plastic bottle.

Video: download1.avi (366 KB)                download2.avi (321 KB)



     1. Fill the plastic bottle with water.

     2. Put glue in one of the straw extremities.

     3. After drying the glue put bread in the straw until it almost floats in the bottle water. (the straw should be practically all submerged)

     4. Close the bottle with the "submarine" inside.

     5. Press the bottle and observe the movements of the "submarine". It begins to submerge?

     6. Stop pressing the bottle. It begins to emerge? Why?

  The home-made submarine that we have just built has an apparent density that makes it float in water. When you press the bottle, due to the almost uncompressibility of water, the volume of air contained inside the "submarine" decreases because it is compressed. Therefore, the "submarine" apparent density increases causing it to submerge. When you stop pressing the bottle, the air pressure returns to the initial state and the air volume inside the "submarine" increases. Then the apparent density decreases and the "submarine" begin immediately to emerge.
The true submarines work in a similar way, using pumps of water that suck water inside or remove it outside to submersion or emersion, respectively. As you see, the science is always there. That is a fascinating world!

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