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6th Grade Science / Lesson 12 - How Can We Use Buoyant Force

How Can We Use Buoyant Force

What will we be learning today?

  • In this lesson, we are going to learn all about how we can use buoyant force.

  • How Can We Use Buoyant Force?

    Submarines can sink, rise, or just "hover" in the ocean. To make the sub sink, the crew pumps seawater into tanks on board. This makes the sub have more weight than buoyant force, so it goes down.


    To make the sub rise, the crew pumps air into the tanks, forcing the water back out into the ocean. Now the sub has less weight than buoyant force, so it goes up.


    If the crew pumps just the right amount of air into the tanks, the sub's weight equals the buoyant force, and it can hover in place.


    Can you float in water? You float better when you take a deep breath. Why? You increased your volume, but you didn't change your mass very much. Your density decreased. Decreasing your density helps you float.


    Why does a rowboat start to sink when it fills up with water? The same volume (the size of the boat) is filling up with more mass. It becomes denser. It starts to sink. To stop from sinking, what do you have to do?