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Drag Force Formula In Fluid Mechanics

Drag Force Formula:

\[ F_d = \frac{1}{2} \rho v^2 C_d A \]

kg/m³
m/s
(dimensionless)

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1. What is Drag Force in Fluid Mechanics?

Definition: Drag force is the resistance force caused by the motion of a body through a fluid (liquid or gas).

Purpose: This calculator helps engineers, physicists, and students determine the aerodynamic or hydrodynamic drag on objects moving through fluids.

2. How Does the Drag Force Formula Work?

The calculator uses the formula:

\[ F_d = \frac{1}{2} \rho v^2 C_d A \]

Where:

Explanation: The formula shows drag force increases with the square of velocity, directly with fluid density, drag coefficient, and reference area.

3. Importance of Drag Force Calculation

Details: Accurate drag calculations are essential for designing vehicles, aircraft, ships, and understanding fluid flow around structures.

4. Using the Calculator

Tips: Enter fluid density (1.225 kg/m³ for air at sea level), velocity, drag coefficient (0.47 for sphere), and reference area. All values must be > 0 (velocity can be 0).

5. Frequently Asked Questions (FAQ)

Q1: What is a typical drag coefficient value?
A: It varies by shape: ~0.47 for sphere, ~1.05 for cube, ~0.04 for streamlined airfoil.

Q2: How do I determine reference area?
A: For most applications, use frontal area (projected area facing flow direction).

Q3: What fluid density should I use?
A: 1.225 kg/m³ for air at 15°C sea level; 1000 kg/m³ for water; check tables for other fluids.

Q4: Does this formula work for all velocities?
A: It works well for subsonic speeds; different considerations apply near or above speed of sound.

Q5: How does drag force affect vehicle design?
A: Higher drag means more energy needed to move, affecting fuel efficiency and maximum speed.

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