This is a conceptual question involving Fluid Mechanics and Buoyancy . 1. Let\'s

Question

This is a conceptual question involving Fluid Mechanics and Buoyancy.

1. Let's say you have a motionless block on a flat surface. The summation of forces in the y-direction is the following:

FN - FG = ma --> FN = FG

When learning Newtonian Mechanics, the summation above is correct. However, why is buoyant force EXCLUDED from the summation of forces? Isn't the Air exerting a buoyant force onto the block, upwards? If so, why is buoyant force not included in the summation? Alot of Physics books also exclude it, so there must be a reason. Is Newtonian Mechanics, practiced, in a vacuum? Such that the block is not surrounded by any type of fluid?

How about the classical problem of a block sliding down an inclined plane? Isnt Air exerting a buoyant force onto the block as it slides down?

Explanation / Answer

It is generally not used because in these cases, Buoyant force << other classical forces, it is not taken into consideration. But when air drag force is considerable, then we take into account of this force.

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