Question

What is drag?
A. Frictional force offered by fluids
B. Friction force offered by a solid surface
C. pulling a body over a surface
D. none of these

Answer 1

Hint: To answer this question we at first need to know about the concept of drag. Then we need to know where drag works, like drag is a force but it does not apply everywhere there are some fixed places or conditions where drag works.

Formula used:
$D=C_d\times A\times 0.5\times \rho \times V^2$

Complete answer:
To understand what is drag we at first have to understand the concept of drag.
Now, we have to know that drag is nothing but a force, whose magnitude depends on some factors such as the square of velocity of the body, the size and shape of the object, density of the air, the viscosity of the air and obviously the inclination of the object to flow.
Therefore the factors on which drag depends are a bit complex to understand.
So, to deal with these complex elements researchers found a way to eliminate all the elements by introducing an element which is drag coefficient.

Mathematically we can represent drag as,
$D=C_d\times A\times 0.5\times \rho \times V^2$
Where, ‘D’ is the drag force, $C_d$ is the drag coefficient, ‘A’ is the cross-sectional area, ‘$V$’ is the velocity and ‘$\rho$’ is the density of the medium in which the body is travelling.

Now, if we consider fluid dynamics, we will see that drag is actually a force that opposes the motion of an object which is going through the fluid, so we can say that drag is a kind of frictional force which acts inside fluids.
So, according to the explanation given above, Option A, Frictional force offered by fluids, is the correct answer.

So, the correct answer is “Option A”.

Note:
Remember that drag is actually a frictional force which acts inside the fluid. The force of lift also has the similar formula as drag force except for the fact that there is lift coefficient. As the formula states that the drag force is directly proportional to the density of fluid, it means, a body will experience more resistance in high density fluids like honey.