|MadSci Network: Physics|
The simple answer is yes, 100 lbs of water *could* support a 1000000 Lb boat. And the reason is counter-intuitive and that is why is hard to comprehend. Of course the words used to describe the scenario are all loaded with implicit meaning, and presume you are envisioning the right situation. So, the usual scenario for this kind of proposition is that you have a container (capable of supporting 1000000 lbs) whose interior matches the (bottom and side)contours of the boat. You then put the boat into this container without any water, with it just sitting in there. Finally, you add the 100 lbs of water into the container, between the boat and the container. Presuming that the boat's total average density is less than 1gm/cm sp.gr. (the density of water), then the boat *will* float on that thin layer of water. The statement that the boat must displace an amount of water equal to its weight is actually incomplete. What it really means is that the boat would displace an equal weight of water if that water previously existed in the same volume way in the first place. This is an resulting effect, not an a priori cause of the phenomena. The 100lbs of water is not doing the ultimate supporting of the boat; the actual support of the boat is being done by the container beneath the 100lbs of water. The mechanism by which the 100lbs of water acts as an intermediate support of the boat is: 1. The pressure of the area of the water touching the boat is equal & opposite at every contact point to the pressure of the bottom/side of the boat. 2. The pressure of the bottom of the boat is equal to the weight of the boat multiplied by its bottom/side surface area. 3. This pressure (which is force/area) is not enough to push a column of water (of any given cross sectional area) above the sides of the container. 4. Thus the 100lbs of water will rise only to the necessary height to counter-balance the less-than-water-dense boat. There are other equivilent explanations for the effect, but this is basically it
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