Question

(a) Define drag.
(b) On what factors does drag depend?

Answer 1

Hint: In order to solve this question we need to understand forces. Force is a pull in a body which causes a body to change its state and from Newton's first law, when a body is subjected to external force then it opposes this behavior. Force is mathematically defined from Newton's second law as, force is equal to change in momentum of a body with respect to time.

Complete answer:
Drag is defined as air resistance. Actually when a body falls in gravity then earth exerts gravitational pull on the body causing it to fall towards ground but as it falls it replaces the air beneath it hence air opposes this behavior and exerts an upward force on body which is proportional to volume of air displaced.

Upward drag force is given by,
${F_d} = \dfrac{1}{2}\rho {v^2}{C_D}A$
Here, $\rho $ is mass density of air, $v$ is velocity with which it falls, ${C_D}$ is drag coefficient and $A$ is surface area of the object.

So drag depends on;
Surface area of object falling- It is directly proportional to surface area.
Velocity- It depends on square of velocity of object while falling
Density- Mass density of air in which it is following

Note: It should be remembered that air resistance has a very crucial role as due to this we cannot feel the pressure of droplets of water in the rainy season on our head but we do feel intense pressure on our heads when someone throws a penny on our head from a building. Due to air resistance droplets speed after sometime become constant as the force due to air and force exerted by earth becomes equal and opposite to each other.