Welcome to brain Stuff from house stuff Works dot com where smart Happens. Hi Am Marshall Brain with today's question, why can boats made out of steel float on water when a steel bar sinks? The standard definition of floating was first recorded by Archimedes and goes something like this. An object in a fluid experiences and upward force equal to the weight of the fluid displaced by the object. So if a boat weighs a thousand pounds, it will sink into the water until it has displaced a thousand
pounds of water. Provided that the boat displaces a thousand pounds of water before the whole thing has submerged, the boat floats. It's not very hard to shape a boat so that the weight of the boat has been displaced before the boat is completely underwater. The reason it's so easy is that a good portion of the interior of any boat is air, unlike a cube of steel, which is solid steel. Throughout 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 a thousand 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 one inch square and one foot tall, it weighs about point four four pounds depending on the temperature of the water. That means that a one foot high column of water exerts point four or four pounds per square inch. If you were to submerge a box with a pressure gauge attached into the water, then the pressure gauge would measure
the pressure of the water at that submerged depth. If you were to submerge this box one foot into the water, the gauge would read point four four p s I. What this means is that the bottom of the box has an upward force being applied to it by that pressure. So if the boxes one ft square and it's submerged one ft deep, the bottom of the box is being pushed up by the water pressure of twelve by twelve inches times point four four pounds per square inch or
sixty two pounds. This just happens to exactly equal the weight of a cubic foot of water that's been displaced. It's this upward water pressure pushing on the bottom of the boat that is causing the boat to float. Each square inch of the boat that's underwater has water pressure pushing it upward, and this combined pressure floats the boat. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at
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