At what density did the aluminum ball sink? At what density was the aluminum ball approximately equal to that of water? For each diameter of the sphere, what is the mass of the water that was displaced?
For more accurate results, continue testing additional cm aluminum squares. Observations and results Did more and more of the ball end up below the top of the water as the ball's diameter decreased? Was about half of the ball below the water when the ball had a diameter of about 2. If an object is floating in water, the amount of water that gets displaced weighs the same as the object. Consequently, while it was floating, the ball should have displaced the same amount of water as it decreased in diameter, and so the buoyant force should have remained the same.
However, the density of the ball was changing—it increased as the ball's diameter decreased. Density is the mass per unit volume—it describes how much "stuff" is packed into a volume of space. When the aluminum ball had a diameter of 6. And as long as the ship displaces enough water to create a strong buoyant force, it can stay afloat—even if it is loaded with cargo. As the diameter decreased and density increased, the ball should have sank more and more.
When its diameter was about 1. This is when the ball had a density approximately equal to that of water. With a diameter of about 1. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science. Key concepts Hydrodynamics Fluid dynamics Physics Water Introduction Have you ever wondered why when you drop a steel nail into water it sinks like a stone, but when a well-built steel ship is in the ocean it floats, even though it weighs much more than a tiny nail?
That means that in order to float an object must have a lower density than the fluid. If the object's density is greater than that of the fluid, it will sink. The density of ships Although ships are made of materials that are much denser than water, the density of a ship itself is its total weight including, cargo, bunkers, stores, crew, etc. This means that the hull must have an external volume that is big enough to give the whole ship a density that is just less than that of the water in which it floats.
Ships are therefore designed to achieve that. Much of the interior of a ship is air compared with a bar of steel, which is solid , so the average density, taking into account the combination of the steel, other materials and the air, can become less than the average density of water.
When the metal hull of a ship is breached, water rushes in and replaces the air in the ship's hull. As a result, the total density of the ship changes and depending on the extent of the change, the ship may sink.
Freeboard In the past, ships built and loaded in Europe would sometimes sink when they reached the tropics for the first time. Cargo would have been loaded in cold, salty waters, but then when the ship reached warmer, less salty seas, it would sink.
This was because Archimedes' principle, described above, would not have been taken into account. When the ship was first loaded it would float because cold, salty water has a higher density than fresh water, which meant that less water had to be displaced to equal the mass of the ship.
Once the ship entered warmer, less salty waters, more water had to be displaced to maintain equilibrium. The ship would drop lower in the water - and if it dropped to below the water line the line where the hull of a ship meets the water surface it would sink.
The average density of a boat -- the combination of the steel and the air -- is very light compared to the average density of water. So very little of the boat actually has to submerge into the water before it has displaced the weight of the boat. The next question to ask involves floating itself. How do the water molecules know when 1, pounds of them have gotten out of the way?
It turns out that the actual act of floating has to do with pressure rather than weight. If you take a column of water 1 inch square and 1 foot tall, it weighs about 0. That means that a 1-foot-high column of water exerts 0. Similarly, a 1-meter-high column of water exerts 9, pascals Pa.
If you were to submerge a box with a pressure gauge attached as shown in this picture into water, then the pressure gauge would measure the pressure of the water at the submerged depth:. If you were to submerge the box 1 foot into the water, the gauge would read 0.
0コメント