
#1
Mar912, 09:19 AM

P: 26

If a body is rotating in a circular orbit then what is the moment of net force acting on it about the axis of rotation?




#3
Mar912, 09:26 AM

P: 26

0 but how?




#4
Mar912, 09:26 AM

Mentor
P: 40,882

a doubt regarding torque 



#5
Mar912, 09:35 AM

P: 26

in gravitation i have read that...
the force on a planet towards radius is given by GMm/r^2 and the force which acts radially outwards is Mv^2/r so dunno where the net force acts... !!!:{ and torque = F X R if the direction of net force is towards center then it makes and angle of 180 degrees which gives ex. torque = 0 as sin 180 = 0 .... but just tell me about the direction of net external force...!! (Thanks in advance) 



#6
Mar912, 10:02 AM

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P: 40,882





#7
Mar1012, 01:17 AM

P: 26

How then do we derive the velocity of a plannet in circular orbit?????
when we equate both of them... v = root[GM/R]...!! 



#8
Mar1012, 02:07 PM

Mentor
P: 40,882

No need for any mysterious outward force. 



#9
Mar1012, 11:20 PM

P: 26

ok.. so u mean both of them acts towards the centre... Right?
since the force on the particle by the center equals GMm/R^2 and also by Newton's second law of motion, F = ma so, F = m x centripetal acceleration (which is towards the center) = m x v^2/r and thus we get, v = root[GM/r] ...? 



#10
Mar1112, 12:18 AM

Emeritus
Sci Advisor
PF Gold
P: 5,198

We're not talking about two distinct forces here. Gravity IS the centripetal force in this situation. Centripetal force is always just a requirement for circular motion. It has to be provided by something real, like gravity, or tension in a string. Without something like this to provide (or act as) a centripetal force, there simply won't be any circular motion. 



#11
Mar1112, 04:02 AM

P: 26

got ur point.... but i too meant the same...
i m nt differentiating the two force i just meant the different expressions for a single force.. the force between them is GMm/r^2 which also equals mv^2/r (the centripetal force which acts towards the center to keep the body rotating in a circular path) and thus gets the formula derived..... 



#12
Mar1112, 04:04 AM

P: 26




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