Question

A streamlined body:
A. increases friction
B. reduces friction
C. decreases weight
D. increases weight

Answer 1

When a body travels through any medium, it experiences a drag force that opposes its motion. The drag force depends on the area on which the molecules of the medium are hitting the body travelling in that medium. When the body is streamlined, this area is reduced to a very small amount.

Complete step-by-step answer :
When a body travels through any medium, it experiences a force that opposes its motion. This force is called the drag force. That is not all the bodies move with the same ease through a medium.
The drag force is always opposite to the direction of the velocity of the body. If you know about frictional force, you can think that the drag force is somewhat similar to the frictional force.
Air also produces a drag force on the objects that travel through it.
Water creates more drag force than air. But how do fishes swim so smoothly through waters?
This is because of the streamlined bodies of the fishes. Streamlined body reduces the friction or the drag force. A streamlined body is bulged in front and narrow ending. This structure allows the body to move smoothly through the medium.
Aeroplanes also have a streamlined body. Submarines are also made of streamlined structure to travel smoothly through the ocean waters.
The drag force depends on the area on which the molecules of the medium are hitting the body travelling in that medium. When the body is streamlined, this area is reduced to a very small amount. Hence, the drag force oppose the motion of the body is small allowing the body to move without much friction.

Note : With this we now know that when a projectile is thrown in the air along with the gravitational force of attraction by the earth, the projectile will also experience a drag force by the air. This force will be in the opposite direction of the velocity of the projectile. This drag force is also known as air resistance.
The point to be noted is that if we consider the air resistance then the formulas for the y of flight, range and maximum height of the projectile will differ from the formulas derived in the ideal conditions.