Question

The primary driving force for natural convection is (a) shear stress forces (b) buoyancy forces (c) pressure forces (d) surface tension forces (e) none of them

Short answer

Answer: Buoyancy forces.

Step-by-step solution

Understand natural convection

Natural convection is the mode of heat transfer that occurs due to the fluid motion caused by differences in density that result from temperature gradients. In simpler terms, it is the heat transfer that occurs when fluid molecules move as a result of temperature differences in a fluid.

Understand different forces

Let's briefly understand each force mentioned in the options: - Shear stress forces: These forces arise from the resistance between two surfaces sliding against each other. - Buoyancy forces: These forces are responsible for the upward force on an object that is less dense than the surrounding fluid. - Pressure forces: These forces result from the force exerted by the fluid on the walls of its container. - Surface tension forces: These forces occur at the boundary between a liquid and gas phase, where the liquid tries to minimize its surface area.

Identify the primary driving force

Now that we understand the forces, we can determine which one acts as the primary driving force for natural convection. Natural convection occurs due to fluid motion resulting from density differences caused by temperature gradients in the fluid. This movement of fluid happens primarily due to buoyancy forces that affect the fluid as a result of varying temperatures. So, the correct answer is: (b) buoyancy forces