How does a steel ship float if it is heavier than water?

Archimedes’ principle states that a body immersed or partially immersed in water loses an amount of weight that is equal to the weight of the fluid it displaces.

Whether or not an object can float depends on the density (weight ÷ volume) of both the object and the water.

If the density of the object is less than that of water, the object will sink into the water only to the point where the weight of displaced water equals the weight of the object. A one foot wooden cube, for example, might weigh 50 pounds.

In water, the submerged part of the cube will displace a volume of water weighing 50 pounds. Because the cube is less dense than water, it needs an equal weight but a smaller volume of water to support it. The force of the displaced water pressing in on all sides is called buoyancy.

If this principle holds, how can a steel ship possibly float, when steel has a density approximately 8 times that of water? In fact, the hull of the ship is filled with air, and air’s density is 816 times less than that of water.

If the overall size and weight of the ship are considered, then, its density is actually less than that of water, and the ship will float.

About Karen Hill

Karen Hill is a freelance writer, editor, and columnist. Born in New York, her work has appeared in the Examiner, Yahoo News, Buzzfeed, among others.

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