PRINCIPLE OF BUOYANCY
[2 Kings 6:4-6]
So he went with them. And when they came to Jordan, they cut down wood.But as one was felling a beam, the axe head fell into the water: and he cried, and said, Alas, master! for it was borrowed.And the man of God said, Where fell it? And he shewed him the place. And he cut down a stick, and cast it in thither; and the iron did swim.
In physics, buoyancy ( /ˈbɔɪ.ənsi/) is a force exerted by a liquid, gas or other fluid, that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the column than at the top. This difference in pressure results in a net force that tends to accelerate an object upwards. The magnitude of that force is proportional to the difference in the pressure between the top and the bottom of the column, and is also equivalent to the weight of the fluid that would otherwise occupy the column. For this reason, an object whose density is greater than that of the fluid in which it is submerged tends to sink. If the object is either less dense than the liquid or is shaped appropriately (as in a boat), the force can keep the object afloat. This can occur only in a reference frame which either has a gravitational field or is accelerating due to a force other than gravity defining a "downward" direction (that is, a non-inertial reference frame). In a situation of fluid statics, the net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body.