Question

What is the primary cause of buoyant force acting on a submerged object?

• A. The object's weight
• B. The pressure difference between the top and bottom of the object
• C. The viscosity of the fluid
• D. The surface tension of the fluid

Hint:

Integrating the vertical components of the hydrostatic pressure forces over any submerged body of volume $V$ mathematically simplifies to $F_B = \rho_{\text{fluid}} \cdot g \cdot V$, proving that pressure variation with depth is the sole cause of buoyancy.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This fluid mechanics question asks for the physical origin of the buoyant force that acts on any object submerged in a fluid.

Step 2: Key Formula or Approach:
The pressure in a static fluid increases linearly with depth:
\[ P = P_0 + \rho g h \]
The net vertical force exerted by the fluid on a submerged body is found by integrating the pressure over the entire surface area of the body.

Step 3: Detailed Explanation:

• When an object is submerged in a fluid, the fluid exerts pressure forces normal to all surfaces of the object.

• Because pressure increases with depth, the bottom surface of the submerged object (which is at a greater depth) experiences a larger upward pressure than the downward pressure acting on the top surface.

• This difference in depth-dependent pressure creates a net upward force on the object.

• This net upward force is the buoyant force, as described by Archimedes' principle.

• Viscosity and surface tension do not cause buoyancy, and the object's weight is a downward gravitational force that opposes buoyancy but does not cause it.

Step 4: Final Answer:
The primary cause of the buoyant force is the pressure difference between the top and bottom of the object.