Submarines are boats that are designed to operate and travel ____. Because they are full of air, like a balloon, submarines do not ____. The air makes them less ____ than the water around them. Many kinds of boats use "ballast," which is any material that adds ____ to make the boat more stable. Ballast can be anything from metal plates to rocks, but ____ use water to make them dense enough to dive ____ into the ocean. In order to store the water it takes in, a ____ has large ballast tanks, which can hold different ____ of water. To make the submarine dive, special operators ____ water into the ballast tanks. Once the controllers have pumped in enough ____, the submarine can begin its ____ into the ocean depths. The speed at which the submarine dives is partially ____ by how quickly the ballast tanks take in water. When the submarine is underwater, operators maintain a steady ____ by pumping some air back into the ballast tanks. In this state, known as "neutral buoyancy," a submarine can ____ around without rising or falling. In order to move through water, the submarine has ____. The propellers are ____ in such a way that they push water forward or backward depending on which way the propellers are ____. The faster the propellers spin, the faster the ____ will travel. Navigators use special equipment that helps pilots steer submarines safely in dark or ____ waters. To return the submarine to the surface, air is ____ into the ballast tanks, which pushes all of the water out. As the amount of ballast in the submarine decreases, the craft once again becomes less ____ and begins to ____.

Submarine Basics

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