Question

The drag force experienced by a body moving through a fluid is mainly due to:

• A. Buoyancy only
• B. Pressure difference and viscous effects
• C. Gravitational force
• D. Surface tension

Hint:

Logic Tip: Stick your hand out the window of a moving car. The air hitting your palm (high pressure) and the air swirling behind it (low pressure) creates pressure drag. The air scraping along the sides of your hand creates viscous drag.

Answer 1

The Correct Option is B

Concept:
Drag is the aerodynamic or hydrodynamic force that opposes an object's motion through a fluid (liquid or gas). It is a mechanical force generated by the interaction and contact of a solid body with a fluid.

Step 1: As an object moves, it physically pushes fluid out of the way. This creates a high-pressure zone immediately in front of the object and a low-pressure wake zone behind it. This pressure difference front-to-back literally pulls the object backward, creating form drag.

Step 2: Because fluids have viscosity (internal stickiness), the fluid molecules physically rub against the surface of the moving object. This friction between the fluid layers and the solid boundary creates a shear stress that opposes motion.

Step 3: Total aerodynamic drag is the sum of these two distinct phenomena: the pressure difference (form drag) and the viscous surface friction (skin friction).

Step 4: Buoyancy and gravity act vertically and govern whether an object floats or sinks, not its resistance to horizontal motion. Surface tension only applies at the interface between two fluids (like air and water), not fully submerged motion.