When we fall on water. The surface molecules are pushed down and as a consequence molecules below the surface molecules and molecules beneath them and so on are also pushed down. Some of them are however displaced. The particles, being pushed, must push us back in reaction. Is that what we call Buoyant Force?
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2 Answers
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Buoyancy is based on the principle that water pressure increases with depth. If something is submerged, the pressure acting upwards on it will be slightly larger than that acting down on it. If this imbalance is larger than the acceleration of gravity the object floats. Buoyancy is also proportional to the volume of the object but acceleration is related to its mass. Therefore the amount of floatation is determined by the density of an object.
You are right however that the pressure is caused by the reaction force of the water molecules on each other and on the object. The same goes for you standing on the ground although the interaction is less complex because it is a solid. There is even the possibility of buoyancy in air as seen with a helium balloon for example. They all underlie the concept of reaction forces.
Look at this article for further clarification: http://hyperphysics.phy-astr.gsu.edu/hbase/pbuoy.html
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No, for the buoyancy force also act for the balloon that calmly float, or to push you up when you swim under the sea level. Buoyancy is a volumetric floating effect, it does not relate to surface or dynamics.
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$\begingroup$ downvoter, please explain. $\endgroup$ Commented Nov 25, 2015 at 19:25