Question

In what direction and at what point does the buoyant force on a body due to liquid act?

Answer 1

Hint: When an object is placed on a liquid, it experiences buoyant force. Let us consider a floating object. The weight of the object pushes it downward but the buoyant force helps it in staying afloat. Also, if the buoyant force exerted different pressure at different parts, it would cause the object to rollover and if it exerted even pressure, the object would stay stable.

Complete step by step solution:
In what direction?
In the direction opposite of the acceleration due to gravity. In regards to Gravity acting downwards, that would be in the “Upward” direction.
 At what point?
At the Centre of Buoyancy. The centre of buoyancy is the centre of the volume of the displaced fluid that is displaced by the object immersed in it.
Gravity acts downwards through the Centre of Mass of the thing, for example a ship.
Buoyancy acts upwards through the centre of buoyancy, the centre of the displaced mass of water, (Basically the total submerged volume of the boat’s hull).
On a boat that is stable and upright while floating, the centre of gravity and the centre of buoyancy are lined up vertically and the two forces balance out and help the boat remain afloat.
When a ship rolls over to one side or another (due to ocean waves or and other forces) , the hull displaces more water from that side and fewer water on the side rolled faraway from .
This shifts the middle of buoyancy outwards from the middle of gravity. The two forces aren't lined up and creates a twisting motion, a “righting moment” which returns the vessel to a good keel (the original position where the centre of buoyancy and the centre of gravity vertically line up).

Note:
If the submerged body has non uniform mass density then the resultant force is applied in what would be its centre of mass if it had uniform mass density. It is the centre of mass of the displaced liquid if this liquid were to be returned in place. It coincides with the “centroid” of the geometrical solid congruent of the body. Therefore the point of action of buoyant force depends on the body shape rather than the body composition.