Question

Smoke particles from a chimney exhibit :
A. Random or irregular motion
B. circular motion only
C. Linear motion only
D. Rotational motion only.

Answer 1

Hint: In fluids we had discussed the type of flow and what are the factors that influence the flow type. Usually there are two kinds of flow. One is streamlined or laminar flow and the other is turbulent flow. Smoke from chimneys comes under one of these flows. It is clearly not linear motion so we can rule it out.

Formula used:
$R = \dfrac{{\rho L}}{A}$

Complete step by step answer:
Linear motion in the sense of motion in a straight line. The smoke from the chimney comes very vigorously so that it will be clearly visible that the flow will not be in a straight line. In case of laminar flow, the lines of flow will be streamlined and parallel to each other. We can clearly predict the pattern of flow at the next point if we know the flow pattern at the previous point. The velocity of flow at a particular point will be constant in magnitude and the direction. It doesn’t vary with time.
Whereas In case of turbulent flow, the lines of flow will not be streamlined and random. We can not predict the pattern of flow at the next point even if we know the flow pattern at the previous point. The velocity of flow at a particular point will not be constant in magnitude and direction. It varies with the time.
So the smoke particles from the chimney is the example for turbulence i.e random and irregular motion.
Hence option A is the answer.

Note:
These random motions play a key role in the aerodynamics of vehicles. The shape of vehicles will be designed in such a way that nowhere the flow pattern will break and will not transfer from laminar to turbulent motion. Because if it happens huge drag will be created and fuel economy will be reduced.