Learn more physics!
How does a submarine ascend?
- Nancy (age 15)
A submarine has big tanks on its side which hold either seawater or
air. Submarines are made out of steel which is heavier than water, and
have a lot of air inside, and float like normal ships when their hollow
spaces are filled with air. However, when the big ballast tanks are
filled with water, the submarine is more dense than water on average,
and sinks. By allowing water to flow into the tanks or by pushing water
out of the tanks, the submarine can control the difference between its
weight and the buoyant force pushing upwards (the total weight of the
water the submarine displaces).
The tanks don't actually have pumps on them. They are filled with
seawater just by opening ports on the side, and the water is pushed out
by forcing compressed air in (the ports have to be on the bottom of the
tank so that water may leave the tanks while the air stays inside).
This process is called "blowing" the tanks.
(republished on 07/31/06)
Follow-up on this answer.