2016 Feb

Centrifugal Force: A Fictitious Force

February 12, 2016

Centrifugal Force

Have you ever experienced the feeling of being pushed to one side when the vehicle you are sitting in takes a steep turn? Have you ever wondered how a washing machine dries clothes? Do you know that the underlying force connecting these two is the same? This force is called as centrifugal force.

Centrifugal force is a pseudo force or fictitious force. It is associated with a particle moving in a curved path or in circular motion. It is also the same force that keeps planets in their orbit and also the electrons moving around the nucleus. When a stone tied to a thread or rope is moved in a circular path, one could feel tension in the rope. In fact, one has to hold the rope tight for it feels like someone is pulling the stone away from you. But there isn’t really anyone pulling the stone or anything that you can attribute that pulling force to. Nevertheless, the force can be felt and such forces are called as fictitious forces. Centrifugal force is one such force. The force that pulls the stone away from you is nothing but centrifugal force.

In technical terms, the line drawn perpendicularly to the rope when stone-rope set up is in circular motion, and also perpendicular to the plane of rotation, is called as axis of rotation. During our Physics tuition class on circular motion, we learnt that the centripetal force acts towards the centre of the circular motion. The centrifugal force, on the other hand, acts along the length of the rope away directed away from the axis of rotation. The magnitude of the force depends on the radius of rotation; if the radius of rotation is high the centrifugal force associated is low and vice-versa. It is directly proportional to the velocity at which the object is moving. Now when you are sitting in a car taking a turn, you are in circular motion for a moment, with radius of rotation being the radius of the curve. Hence, centrifugal force acts on you, pulling you away from the axis of rotation along the radius of the curve. Suppose if you are turning left you are pulled towards your right and vice-versa.

Coming to the question of drying clothes in a washing machine. Washing machines are generally equipped with a centrifuge. A centrifuge is a drum like device with small holes (like that on a mesh) on its walls. When a centrifuge with wet clothes is rotated at high speeds the clothes are pulled towards the walls because of the centrifugal force and since the walls are porous the clothes get stuck there but since water can move through these holes water is pulled out of the drum by centrifugal force and thus the clothes are dried. Centrifugal force, since is directed away from the axis of rotation, counters gravity or electrostatic pull in the case of planets and charged particles, and prevents the solar system and atoms from collapsing.

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