Buoyancy

FLOTATION DEVICES

• Scuba divers wear BC (buoyancy compensator) equipment to adjust and control their buoyancy while underwater.
• Freedom Ship, an ocean vessel in development, will be the world’s biggest ship floating on water. At one mile long and 25 stories high, engineers envision it as the first ever floating city, with 50,000 permanent residents, a hospital, parks, schools, and shopping malls. The ship will circle the world every two years in a never-ending cruise.

“EUREKA!”

As the story goes, when Archimedes-a mathematician in ancient Greece-stepped into the bathtub one day, the answer to a problem that had troubled him for some time became clear. Calling out “eureka” (”I have found it” ), he jumped out of the tub and ran naked through the streets to share his discovery.

Here’s what he realized: The water level in the bathtub rose when Archimedes climbed in, because things put into water always displace the water at least a little bit to make room. When the weight of the object is more than the water it displaces, it sinks (negative buoyancy). However, when the object is lighter than the water it displaces, it floats in the water (positive buoyancy).

Cruise ships, which are heavy, float because par ts of the boat that are underwater are hollow and contain just air. This adds to the ship’s size, but not its weight. Thus, the weig ht of the water the ship displaces becomes more than the ship’s weight, and as a result, the ship floats. Submarines are able to both float and sink. A submarine resting on the surface has special ballast tanks filled with air. When it wants to sink, the sub lets in seawater to fill the ballast tanks and make the sub heavier. To rise once more, compressed air is blow n into the tanks, forcing out the water and making the submarine lighter.