Drag Force Calculation

Drag Force

The drag force is dependent on the geometry and size of the object, the density of the air, the velocity of the object, and the so-called Reynolds number. In this implementation, the equation describing the drag force has been taken from the book Physics for Game Programmers, equation 7.51 on page 191, defined as:

• F_D = 1/2 ρ v^2 A C_D

where ρ is the air density, v is the velocity of the ball, A is the cross-sectional area of the ball, and C_D is the drag coefficient. The drag coefficient is dependent on the Reynolds number, which is in turn dependent on the air density, the velocity of the object, the cross-sectional area, and the viscosity. In Physics for Game Programmers, experimental data is used to describe C_D. This results in the following:

• C_D = 0.47 if Re< 100000
• C_D = 0.47 - 0.25*(Re -100000)/35000 if 100000 < Re < 135000
• C_D = 0.22 if Re > 135000

where Re is the Reynolds number.

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