Question

When milk is churned, the cream is separated from it due to:
A) Frictional force
B) Cohesive force
C) Gravitational force
D) Centrifugal force

Answer 1

Hint: Whenever a body is subjected to a circular motion, then the force which acts in the direction of its center is called centrifugal force. This force keeps the body on a circular track. While other forces are not responsible for circular motion. Churning is the process of separating the cream from milk by rotating milk in a circular motion at high speed. While rotating centrifugal force acts on it.

Complete answer:
When milk is churned, the cream is separated from it due to centrifugal force because this force acts outwards in the direction of line joining centre to the locus. Due to outward force the heavier particles in milk experiences more force than the lighter particle. The cream part, being a heavier part, it separates from the milk and it gets churned out. Here, rest forces are not in major roles. The frictional force is less when milk is churned at high speed.

Cohesive force tends to bind the particles with each other. Whereas gravitational force does not act in noticeable magnitude. The only force used in churning is centrifugal force. The force which acts towards the centre is called centripetal force. These both centrifugal and centripetal forces keep the body in a circular motion. Whenever a body is rotated at high speed, its constituents tend to get separated from each other due to the variation in masses. This phenomenon is used in such processes called churning and the process of rotating liquids at high speed is called centrifugation.

Therefore, Option (D) is the correct answer.

Note: While all the forces are acting on the milk but the major force due to which the process of churning is done is centrifugal force. Maybe other forces can play major roles in some other applications, but for circular motion centrifugal and centripetal forces are the major forces.