Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Centripetal and Centrifugal force


Centrifugal force is often vaguely understood concept for a large number of students (and teachers). Sometimes it is said to be reaction of centripetal force, sometimes pseudo force and so on. The proper use of rotating frame has to be practiced.


A rotating disk, a long tube which may be closed at the ends, foam and stone pieces, hanging threads.


  1. Look at the rotating disk assembly. You can hold it in one hand with the disk in horizontal plane and rotate it by giving a gentle jerk with your other hand.
  2. Fill water in the tube, put few pieces of foam and few pieces of stone into this water and close it.
  3. Fix the tube on the disk. By tilting the disk several times, spread foams and stones throughout the tube.
  4. Now give a sharp rotation to the disk and let it stop on its own. Make sure that the disk remains horizontal. Where are the foam particles? And where are the stone particles? Explain on the basis of centrifugal force and centripetal force.