IIT JEE , AIEEE Forum - Physics , Mechanics

sudeep.kumar

Well.. a nice doubt where most people get confused...

First, centripetal force...

Any force which provides centripetal acceleration to a body is called a centripetal force.
So, earth is revolving due to the centripetal force.. which is actually gravitational force of sun.. so centripetal force is not a type of force.. it may be gravitational.. may be electrostatic ..etc in nature.. all that it should do is to provide centripetal acceleration.

Now the actual culprit..
All of you must be knowing pseudo force..
When the 'observer' is looking at a body from a non inertial frame (no matter weather the body is at rest, in linear motion, circular motion or whatsoever), then he adds the term of pseudo force so that he could apply newton's 2nd law.. so that he could get sum of all forces, including the pseudo force equal to the mass times the acceleration. Pseudo forces have no existence.. they are mathematical terms used by obsrevers in non inertial frame.

so centrifugal force is a pseudo force.. if we are moving with linear acceleration a, ie the observer is moving with accn a, he adds -ma to all the real forces on anything he observs.
similarly if the observer is rotating with ang vel w, he add the term mw²r in radially outwards direction to use newton's 2nd law.

so if u r rotating with w, but the body is at REST (wtr ground).. at a distance r from the centre of rotation of ur frame (ie centre about which u r rotating), then also u will add mw²r as a virtual force to get mass times accn.

similarly, if u r rotating with w₁ and the body being observed by u is rotating with w_2,then centrifugal force is mw₁²r and not m(w₁-w₂)²r or mw₂²r..etc..

So in summary, if YOU are rotating with w, whatever the body is doing, u must add mw²r to the real forces acting on the body to get ma of the body.. where a is in your frame.. as observed by u.

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