SUBMARINE ACTION

A submarine dives by making itself heavier so that it sinks. It surfaces again by making itself lighter. Submarine use large tanks called buoyancy tanks. When the submarine is on the surface, these tanks are full of air. To make the submarine dive, the tanks are flooded with seawater, making the submarine heavy enough to sink. To make the submarine surface again, compressed air is pumped into the tanks, forcing the water out. This makes the submarine lighter and it floats to the surface. When submarines are underwater, they move up and down using tiny wings called hydroplanes. These work like rudders to strong hulls to prevent them from being crushed by the huge pressure under the water. As submarines dive, the weight of the water pressing down on them becomes greater and greater. You can see how this works by making this model.

Parts of a submarine
A modern submarine, such as this nuclear ballistic missile submarine, is almost as long as a football field - 100yd. It has an engine and propeller at the stern, and is operated by a crew of 140. Steam drives the turbines that turn the propeller. A submarine's hull is strong, but few submarines can go below 1,600ft.

MAKE A SUBMARINE

Large plastic bottle, sand, plastic funnel, tank of water, two small plastic bottles, bradawl, scissors, ruler, two plastic drinking straws, rubber bands, nonhardening modeling material, two bulldog clips.

STEP 1
Fill the large plastic bottle with sand using a funnel. Fill it until it just sinks in a tank of water. Test the bottle to find the right amount of sand.

STEP 2
Make a large hole in one side of two small plastic bottles. On the other side make a small hole, big enough for a plastic straw to fit into.

STEP 3
Attach the two small bottles to both sides of the large bottle using rubber bands. Twist the small bottles so that the small hole on the each one points upward.

STEP 4
Push a plastic straw into each small hole, so that a bit pokes through. Seal around the base of the straws with modeling material to make a watertight joint.

STEP 5
Put a small bulldog clip about halfway down each straw. The clips need to be strong enough to squash the straw and stop air from being forced out by the water.

STEP 6
Put your model submarine in a tank of water. With the clips on, it should float. Remove the clips and water will flood the buoyancy tanks. The submarine will sink.

STEP 7
To make the submarine surface again, blow slowly into both straws at once. The air will force the water out of the buoyancy tanks, and the submarine will rise to the surface.

STEP 8
When your model submarine has resurfaced, keep blowing slowly into the tanks. Replace each bulldog clip and your model submarine will remain floating on the surface.