Question

The motion of a dust particle in air is an example of –
A. Rectilinear motion
B. Curvilinear motion
C. Oscillatory motion
D. Random motion

Answer 1

Let’s first try to know each type of motion mentioned in the option and how they behave. Later try to compare air particle motion, which follows a zig-zag movement and randomly chooses the path.

Complete step by step answer:
Firstly, we are going to take a look at different motions. So, what is rectilinear motion? As we know that the particle’s having a body travel with the same distance along parallel straight lines, the motion is said to be Rectilinear Motion. For Curvilinear motion we know as the motion in curve path, e.g., in Roller coaster the path has a curve and is known as curvilinear motion. Secondly, throwing a store in the air at an angle is the curvilinear motion of the stone.
So, we know that the air which is a fluid doesn’t follow any above 2 specifications and we processed with the option by eliminating the above 2.
Now in Oscillatory motion, it can be termed as to and fro motion where the motion is repeatedly continuous with the mean position. It is only possible in a non-friction place whereas this is not possible in this world for having a non-friction plane. Whereas this too doesn’t follow motion which air follows and leads to the option no 3 is also incorrect.
Now let’s check option no 4, which is random motion and it follows a zig-zag moment of the particle. Being zig-zag in motion it is unpredictable motion. This type of motion object follows any direction, and continuously changes its way. as we know that Brownian motion has an erratic random movement of microscopic particles in a fluid, and results in continuous bombardment from molecules surrounding. Here air too has a movement in unpredictable direction and bombard with other surrounding particles.
As we know that the Brownian motion is also a random motion and we concluded out that air follows the random motion.

So, the correct answer is “Option D”.

Note: Try to check each and every motion and eliminate accordingly, secondly air follows Brownian movement but it is also a random motion. Brownian movement is a physical phenomenon where quantity undergoes small and random fluctuation.