Question

A ________ is a water tight boat and can travel underwater like a normal ship on the surface of the water.

Answer 1

1. A submarine can float when the mass of water that it displaces is equal to the mass of the boat.
2. This displaced water causes an upward force called buoyancy.
3. Buoyancy acts in the opposite direction to gravity, which would pull the ship down.
4. A regular boat cannot control or change its buoyancy, but a submarine can.
5. This allows a submarine to dive under the water or to come up.
6. It is used for independent operation underwater.
7. Submarines can stay underwater for three months almost.
8. 

Hence, a Submarine is a water-tight boat and can travel underwater like a normal ship on the surface of the water.