NOVA

Hitler's Lost Sub

Student Handout

Build Your Own Submarine

A submarine is not just a silent shape gliding smoothly along under the sea. The submarine's crew is constantly making adjustments to keep it from bobbing to the surface or sinking below its safe depth. Here's an activity that lets you be the submarine captain.

illustration of homemade submarine

Procedure

  1. Your teacher will demonstrate how to make your submarine. Use markers to name your submarine.

  2. Fill your soda bottle "diving tank" to within a half-inch (12.7 mm) of the top and stir in a few drops of dishwashing liquid. Place your submarine bottom-side up in the tank where it will float like an actual submarine floats on the surface.

  3. Sink the submarine by pushing lightly with your finger. What happens when you release it?

  4. paperclip ballast

    Carefully add ballast by hanging pieces of paper-clip wire and metal washers to the paper clip hanging from your submarine until it starts to dive. What happens to the submarine as you add more ballast?

  5. Now for the challenging part. Can you make your submarine behave like a real submarine? Can you get the ballast just right so that it is neutrally buoyant, that is, its weight is equal to the water's buoyant force? You'll know you have succeeded if your submarine goes neither up nor down—it stays at the depth it is at.

Questions
Write your answers on a separate sheet of paper.

  1. Imagine that you're a U-boat captain. You've sighted your target and are about to launch two 2,000-pound (0.9-metric ton) torpedoes from your forward torpedo room. Destroyers heavily patrol the surface. Whoosh! Your bow just got 4,000 pounds (1.8 metric tons) lighter. Think about what you learned about buoyancy. What is going to happen to the submarine? What will you do in response?

  2. The Straits of Gibraltar, an entrance to the Mediterranean Sea, is a narrow stretch of water. The water lies in two layers—a lower, saltier layer that is more dense than the surface layer above. The surface layer moves into the Mediterranean and the lower layer moves into the Straits. If you were a U-boat commander, how might you take advantage of this knowledge so that you could enter and leave the Mediterranean silently?




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