Book 6, Question 110
Why Does a Submarine Go Up and Down?
A submarine has special tanks called ballast tanks. Filling them with seawater makes the sub heavier than the water it pushes aside, so it sinks. Blowing the water out with air makes it lighter, so it rises!
From the book
Page from A Million Whys Book 6
More fun facts
- Real submarines are built to weigh almost the same as the water around them, for their size.
- Big tanks called ballast tanks fill with water to make a submarine heavier, so it sinks.
- To rise, a submarine pushes the water out of its tanks with compressed air.
- In one early test, a submarine stayed 24 hours under 30 feet of water with 16 crew and came up with everyone in good shape.
- Because air flows a lot like water, a Navy submarine model was once tested in a NASA wind tunnel.
Sources: BBC, Scientific American, NASA
Questions kids ask
How does a submarine sink on purpose?
It lets water into its ballast tanks, which makes it heavier.