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Main Question or Discussion Point
Why drag force doesn't Depend on the mass of the Object?
That's the air density, not the object's density.The drag equation suggests it's the object's density, cross-sectional area, and shape that affects the force acting on it by the air.
Sorry, yes, you're right. I'm not sure how I forgot that.That's the air density, not the object's density.
The "drag equation" also is not based upon first principles and does not capture all of the relevant physics contributing to drag. It's just an empirical relationship between the drag force, area, and the dynamic pressure (##\rho V^2/2##). The drag coefficient relates those quantities across a wide range of conditions, but tells you nothing about what actually contributes to the drag. Viscosity, ratio of specific heats, and Mach number can also all play a role, for example. So can the laminar-turbulent state of the boundary layer, the surface quality, and in extremely high-speed flows, chemical reactions.The drag equation suggests it's the object's density, cross-sectional area, and shape that affects the force acting on it by the air.