Imagine that an object is falling through a long straight glass tube held vertical, air has been removed completely from the tube. The object does not touch the walls of the tube. Will the object experience any force of friction?

As the air has been removed from the tube, there is no air particle to resist the motion of a falling object moreover, it does not touch the walls of the tube, so there is no friction offered from the walls of tubes as there is no contact between the surfaces. 

So, the falling object will not experience any friction.


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