DRAG

Calculates the drag coefficient from force, projected area, velocity, and fluid density.

Excel Usage

=DRAG(F, A, V, rho)

• F (float, required): Drag force in Newtons (N)
• A (float, required): Projected area in square meters (m²)
• V (float, required): Velocity in meters per second (m/s)
• rho (float, required): Fluid density in kilograms per cubic meter (kg/m³)

Returns (float): Drag coefficient (float), or error message string.

Example 1: High drag force on a very small projected area

Inputs:

F	A	V	rho
1000	0.0001	5	2000

Excel formula:

=DRAG(1000, 0.0001, 5, 2000)

Expected output:

400

Example 2: Moderate force on a large frontal area

Inputs:

F	A	V	rho
500	0.05	10	1000

Excel formula:

=DRAG(500, 0.05, 10, 1000)

Expected output:

0.2

Example 3: Moderate area with intermediate fluid properties

Inputs:

F	A	V	rho
250	0.02	8	900

Excel formula:

=DRAG(250, 0.02, 8, 900)

Expected output:

0.434028

Example 4: Low force but very high velocity in a light fluid

Inputs:

F	A	V	rho
120	0.01	15	1.2

Excel formula:

=DRAG(120, 0.01, 15, 1.2)

Expected output:

88.8889

Python Code

Show Code

from fluids.core import Drag as fluids_drag

def drag(F, A, V, rho):
    """
    Calculate the drag coefficient (dimensionless) for an object in a fluid.

    See: https://fluids.readthedocs.io/fluids.core.html

    This example function is provided as-is without any representation of accuracy.

    Args:
        F (float): Drag force in Newtons (N)
        A (float): Projected area in square meters (m²)
        V (float): Velocity in meters per second (m/s)
        rho (float): Fluid density in kilograms per cubic meter (kg/m³)

    Returns:
        float: Drag coefficient (float), or error message string.
    """
    try:
      F_val = float(F)
      A_val = float(A)
      V_val = float(V)
      rho_val = float(rho)

      if A_val == 0:
        return "Error: area cannot be zero."
      if V_val == 0:
        return "Error: velocity cannot be zero."
      if rho_val == 0:
        return "Error: density cannot be zero."
      if A_val < 0:
        return "Error: area must be positive."
      if rho_val < 0:
        return "Error: density must be positive."

      result = fluids_drag(F_val, A_val, V_val, rho_val)
      return float(result)
    except Exception as e:
      return f"Error: {str(e)}"

Online Calculator

F *

Drag force in Newtons (N)

A *

Projected area in square meters (m²)

V *

Velocity in meters per second (m/s)

rho *

Fluid density in kilograms per cubic meter (kg/m³)