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Drag Force Equation Fluid Mechanics

Drag Force Formula:

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

kg/m³
m/s

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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: Understanding drag force is essential in designing vehicles, aircraft, ships, and structures exposed to fluid flow.

2. How Does the Drag Force Equation Work?

The calculator uses the formula:

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

Where:

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

3. Importance of Drag Force Calculation

Details: Accurate drag force calculations are crucial for determining power requirements, fuel efficiency, structural integrity, and performance in fluid environments.

4. Using the Calculator

Tips: Enter fluid density (1.225 kg/m³ for air at sea level), velocity, drag coefficient (default 0.82 for a sphere), and reference area. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical drag coefficient value?
A: It varies by shape: ~0.47 for sphere, ~1.28 for flat plate perpendicular to flow, ~0.04 for streamlined airfoil.

Q2: How does velocity affect drag force?
A: Drag increases with the square of velocity - double the speed quadruples the drag force.

Q3: What is reference area?
A: Typically the frontal area (projected area perpendicular to flow direction) of the object.

Q4: What's the density of water vs air?
A: Air ~1.225 kg/m³ at sea level, water ~1000 kg/m³ (varies with temperature and salinity).

Q5: How is drag coefficient determined?
A: Through wind tunnel testing, CFD simulations, or empirical data for standard shapes.

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