# Drag Force: Mass & Why It Doesn't Affect Object

In summary: The drag force is a direct result of the air flowing around the object and is independent of the object's mass or density.
Why drag force doesn't Depend on the mass of the Object?

Well, what does drag force depend on?

if the drag force is the reaction force on the elastic collision between air molecules and the object , so it have to depend on the momentum of the air molecules and object momentum, is that right?

Drag force (and all aerodynamic forces) are the forces caused by the air flowing around an object. Only the shape of the object matters. It doesn't matter if the object is hollow or filled with lead.

okay ,but if you see it as a collision and the air molecule mass is constant and its initial velocity is also constant, and the object velocity is also constant but its mass is changing so the reaction force will change , so drag force must depend mass.

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.

A Lazy Shisno said:
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.
That's the air density, not the object's density.

FactChecker said:
That's the air density, not the object's density.
Sorry, yes, you're right. I'm not sure how I forgot that.

A Lazy Shisno said:
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.

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 important thing is that in none of those cases does the mass (or density) of the object play a role.

FactChecker

## 1. What is drag force?

Drag force is a type of force that opposes the motion of an object through a fluid (such as air or water).

## 2. How does drag force affect an object?

Drag force can slow down the motion of an object or even bring it to a complete stop.

## 3. Does an object's mass affect the drag force?

No, an object's mass does not directly affect the drag force it experiences. Drag force is dependent on the object's shape, velocity, and the properties of the fluid it is moving through.

## 4. Why doesn't an object's mass affect the drag force?

Drag force is a result of the interaction between the object and the fluid it is moving through. The mass of the object does not play a significant role in this interaction.

## 5. Can drag force be reduced or eliminated?

Yes, drag force can be reduced or eliminated by changing the shape of the object, reducing its velocity, or by changing the properties of the fluid it is moving through.

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