Question

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. The frictional force on the object will be ____________.

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• A. proportional to its surface area
• B. proportional to its velocity
• C. equal to zero
• D. proportional to its mass.

Answer 1

The correct option is C equal to zero

Due to the absence of air, there is nothing to provide friction.
Friction arises when molecules of air provide resistance. The absence of any medium removes friction.
Hence, frictional force on the object is zero.