This calculator computes the drag force Fd acting on a smooth or dimpled sphere (like a golf ball). The drag force is defined as 1/2*Cd*A*U^2*rho, with Cd the drag coefficient, A the frontal area of the sphere, U the mean flow speed and rho the density of the flowing medium.
The drag coefficient is a function of the Reynolds number Re, which depends on the flow velocity, the diameter of the sphere and the kinematic viscosity of the flowing medium. The functions relating Cd and Re were obtained by fitting experimental data by Bearman & Harvey (1976). Both the density and viscosity are selected by choosing the medium and temperature. The dependence of these on the temperature were obtained fromWhite- Fluid Mechanics, Kuethe & Chowe- Foundations of aerodynamics and Shevell- Fundamentals of flight.
A difference in Cd, and hence the drag force, is observed for Reynolds numbers greater than 40,000. An explanation of why a difference in the drag occurs, can be found here (a Scientific American web page).
Note that the results are only valid for subsonic velocities.

Instructions: choose the type of ball, medium and temperature, fill in the values for the diameter and the velocity, and then click on "Calculate".
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