Question

What is drag?

Answer 1

Hint: Whenever an object moves in a fluid like a liquid or air, it experiences an opposing force which tries to hinder the motion of the object. This force arises due to friction between the object and the medium through which it travels.

Complete step by step solution:
The drag can be defined as an opposing force which an object may experience when it moves through a fluid like a liquid or a gas. This force tries to hinder the motion of the object moving with respect to the particle of the medium. This force arises due to the fact that the particle of the medium coming in contact with the object interacts with the surface of the object in such a way that a frictional force comes into action.
This frictional force of a fluid is characterized by its viscosity. A fluid with high viscosity exerts larger force which makes motion of the object difficult in that medium.
The drag force also depends on the density of the medium. Greater the number of particles in a fluid, greater is the interaction between the fluid and the object and greater is the drag force exerted by the fluid on the motion of the object. This means that the drag force applied by liquids is larger than the drag force applied by air.
Higher the velocity of the object in a medium, higher is the drag force experienced by the object.
The expression for drag force can be given as
$D = \dfrac{{{C_d}\rho {V^2}A}}{2}$
Here ${C_d}$ is known as the drag coefficient, $\rho $ is the density of the medium, V is the velocity of the object while A is the cross-sectional area of the object.

Note: The drag force is an undesirable effect in case of aerodynamics because we wish to obtain high speed which is hindered by the drag force on the flying object. This force can be reduced by streamlining the shape of the body of the aircraft.