If you doubt that the water exerts an upward pressure, try to submerge a balloon in the bathtub. You’ll feel a substantial upward push that resists your downward push.
When we lowered the Admiral Nimitz into our giant bathtub, the water level rose; it got deeper. As every diver knows, deeper water means higher pressure. This increased pressure is present everywhere throughout the water in the bathtub, because water cannot cushion or absorb a force, the way a spring or a piece of rubber can.
The water must transmit its increased pressure in all directions to everything it is in contact with, including the ship’s hull. All the north-east-south-west horizontal pushes on the hull cancel each other out, leaving only an uncanceled upward push. This is the pressure that pushes the ship upward against gravity. Voila! Buoyancy.
Okay, I know what you’re thinking. Aircraft carriers operate much more frequently in oceans than in bathtubs. Am I telling you that the level of the ocean was raised when the Nimitz was launched? I certainly am.
Spread that one hundred thousand tons of water over the surface of the entire Atlantic Ocean, though, and it comes to a pretty meager rise, quite unlikely to flood any beachfront property in Florida. Nevertheless, it’s a volume of water equal to the submerged volume of the ship’s hull up to the water line, and a buoyant force equal to that weight of water is still operating on the ship.
By the way, Archimedes didn’t have an aircraft carrier at his disposal so, as the story goes, he used his own body. He filled his bathtub to the brim, climbed in, and realized that the weight of the overflow water on the floor had to be the same as his loss of weight, his buoyancy, in the water. History does not record the reaction of his landlady.
In other news.
Exactly why does a hole in the hull of a ship make it sink?
Water rushes in through the hole because it is under a pressure, depending on how deep below the surface the hole is, the lower the hole, the harder the water rushes in. As the water enters the ship, it replaces an equal volume of air, thereby increasing the ship’s weight and hence its overall density.
When enough water has entered to make enough extra weight to overcome the buoyancy force, down she goes.
Related Posts
-
How Do Toadstools Grow Through the Pavement and Why Do Mushrooms Push Up Through the Sidewalk?
Toadstools that force their way up through asphalt are probably ink-cap mushrooms (Coprinus) growing on buried plant debris. They are pushing upwards because their stalks function as vertical hydraulic jacks. The upward pressure…
-
Who discovered the fundamental principles of Levers and Buoyancy in physics and engineering?
The concepts of buoyancy (water pushes up on an object with a force equal to the weight of water that the object displaces) and of levers (a force pushing down on one side…
-
How Do Submarines Change Their Buoyancy To Sink and Float?
Very simply. They change their amount of internal air space, thereby changing their density. You want to dive? You let water into your ballast tanks. You want to surface? You blow the water…
-
How do rockets work in space if there is no air to push against?
It's a good question. You'd think that a rocket's exhaust has to push against something, like a paddle needs to push against water to propel a canoe. But in reality, a rocket doesn't…
-
How Do You Push a Big Ship Like the Queen Elizabeth II With Your Hands and Overcome Static Friction?
It's possible to move a large ship like Navy destroyer with your bare hands, by leaning against a stanchion on one ship, with both hands across the narrow gap to a similar stanchion…
-
Why Does Squinting Your Eyes Improve Vision and Make Objects Appear Sharper If You’re Nearsighted?
Squinting your eyes often makes objects appear sharper, even more so if you're shortsighted. It's because the rays are focused on the retina more than a change in the shape of the eyeball.…
