Museum of Science and Industry

Design a Submarine

Design a mini submarine that moves in the water like a real submarine.

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Lesson at a glance

How do submarines sink and float?  Explore the relationship between density, buoyancy and gravity in this inquiry-based lesson.

Students Will Know:
Buoyancy - The buoyant force is the net upward force (or uplift) exerted by a fluid on a submerged object
Density = mass / volume
Students Will Be Able To:
Explain how the relationship between density and the forces of gravity and buoyancy are manipulated to achieve floating, sinking, and hovering on a submarine.

Illinois Learning Standards

Late Elementary
State Goal 11: A.2a; A.2b; A.2c; A.2d; A.2e; B.2a; B.2b; B.2c; B.2d; B.2e; B.2f
State Goal 12: D.2b
Middle / Junior High
State Goal 11: A.3a; A.3b; A.3c; A.3d; A.3f; A.3g; B.3a; B.3b; B.3c; B.3d; B.3e; B.3f
State Goal 12: D.3a; D.3b

Background Information

Submarines achieve floating, sinking and hovering by filling the ballast tanks with different amounts of water. As the tanks fill with more water, the submarine’s density increases.    

Density is defined as weight per volume. The formula is Density = Mass/Volume. In the submarine, the volume stays constant. The density changes by adding or taking away the different objects.

When two or more forces act on an object, the result is the cumulative effect of those forces. The buoyant force is the net upward force (or uplift) exerted by a fluid on a submerged object. Gravity counters this force by pulling down on an object while the buoyant pushes the object up. If an object’s density is more than that of the liquid, it will sink (force of gravity is greater than the buoyant force). If an object’s density is less than that of the liquid, then it will float (force of gravity is less than the buoyant force). If an object’s density is the same as that of the liquid, it will hover (force of gravity is equal to the buoyant force).