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Buoyant force concept and terminal velocity? My aerodynamics book(John Anderson Aerodynamics) say that whenever a body moves through a fluid, there are only two types of forces acting on the body. 1. Pressure force that acts perpendicular to the plane of the body and the other is the drag force that acts parallel to the objects velocity.

 

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Also i read an article that buoyant force is related to static fluids not moving fluids. Now, i was working on a concept of terminal velocity of an object moving through air in the Z direction. According to my concept, the air is continuously in motion and hence its a dynamic fluid. So, accordingly, the body falling through air will experience friction drag parallel to the velocity and pressure force perpendicular to the velocity. But as i was going through the derivation of the terminal velocity, they have counted the buoyant force in which is completely confusing me. If there is buoyant force when the body is moving through a moving fluid then when an aircraft is cruising at an altitude, why do they not mention the buoyant force? Rather they say that the vertical force is the pressure force which is also the lift force. I am really confused when to apply buoyancy and the concept of this pressure force which acts perpendicular to the plane of the body Please help me.

 

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