Drag Equation Calculator

What Is Aerodynamic Drag?

Aerodynamic drag is the resistive force a fluid exerts on a moving object. Cars, aircraft, and projectiles all experience drag that increases rapidly with speed. Understanding drag is essential for vehicle design, sports engineering, and ballistics.

Drag Equation Formula

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

where $F_d$ is drag force (N), $\rho$ is fluid density (kg/m³), $v$ is velocity (m/s), $C_d$ is the drag coefficient (dimensionless), and $A$ is the reference frontal area (m²). At sea level, air density is about 1.225 kg/m³.

Typical Drag Coefficients

A streamlined car has $C_d \approx 0.25$ to 0.35. A flat plate perpendicular to flow has $C_d \approx 1.0$. A sphere has $C_d \approx 0.47$. Drag force grows with the square of velocity, so doubling speed quadruples drag.

Frequently Asked Questions

Why does drag increase with velocity squared?

Both the momentum of air particles hitting the object and the rate at which they arrive scale with velocity. Together this gives a v² dependence.

What air density should I use?

1.225 kg/m³ at sea level and 15°C. Density decreases with altitude. At 5,000 m it is about 0.736 kg/m³.

What is the drag coefficient?

A dimensionless number describing how streamlined a shape is. Lower values mean less drag for the same size and speed.

Does this work for objects in water?

Yes. Use water density (about 1000 kg/m³) instead of air density. Water drag is much higher due to higher density.

What frontal area should I use?

Use the cross-sectional area perpendicular to the flow direction. For a car, this is the area seen from the front.

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What Is Aerodynamic Drag?

Drag Equation Formula

Typical Drag Coefficients

Frequently Asked Questions

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