Jiten and Subimal:
Thank you both for your responses.
Jiten, when I wrote my latest post, your response was not posted and that is why I wanted to confirm whether you were the classmate I knew. I was burnt once on this score before when I sent an email who I thought was my former classmate. I was deeply hurt. I found out later that I had sent this email to the wrong person with the same name and similar academic background. Therefore, I wanted to absolutely make sure that you were the Jiten I knew. Your post confirmed that fact. I will take this opportunity, after more than two decades, to thank you for your nice wedding present. I am very happy to hear from you again.
Subimal, I appreciate your conferring me the status of "boro bhai," Deshi style, just because my younger brother was your classmate. That is very heart warming. This is one of the nice things I love about our Bengali or South Asian culture, which no amount of westernization has been able to erase so far.
Turning to the subject at hand, it seems Subimal completely agrees with my explanation while there may be some lingering doubts in Jiten's mind. If that is the case, I want Jiten to think about the following thought experiment. Jiten, assume that you are standing in a rotating platform with a pole at its center and a person is tied by a rope to the pole (you can make me that person if you want to subject me to some friendly torture -:). Let us say that we will decide whether there is a centrifugal force (outward radial) by cutting the rope and observe which direction the swirling person is flung. If he is flung in the radial direction, we will conclude that there is a centrifugal force that was balancing the tension in the rope. On the other hand, if he is flung in the tangential direction, then we would conclude that there was no such centrifugal force and that the person was being kept from flying in the tangential direction by the tension in the rope. Finally, assume that Subimal is observing the event from outside the rotating platfrom.
After running this experiment through one's mind, one can come to the following conclusion. Jiten will see the person flung out in the radial direction and Subimal will see the person flung out in the tangential direction. The two observations can be reconciled by noting that when the person moves a certain distance along the tangent, the platfrom and Jiten also move a certain distance in the circular direction, and Jiten, the rope and the person's direction of travel will be aligned and it will appear to be the outward radial direction. So, Jiten will observe what may appear to be the effect of a centrifugal force on the rotating person while Subimal will see no such force. The rotating person will feel an outward radial pressure while tied to the rope. Once the rope is cut, this person will feel being flung out radially if he keeps looking at the center of the platform but tangentially if he looks outside the platform. I hope this thought experiment further clarifies my earlier expalanation.
The magnitude of this force, whether centripetal or centrfugal, is mv**2/r and can be derived by doing simple vector algebra of velocity components at any point on the circle. As to Subimal's point of Newton's laws not holding in non-inertial frames, you are right. That is precisely why it is necessary to introduce the "pseudo force."
On the other hand, if Jiten was completely convinced by the explanation in my earlier post, please ignore the last three paragraphs of this post and we can move on.
Best wishes,
M. Harun uz Zaman
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