Science doubts.....

Topic started by ray of hope (@ on Fri Oct 25 12:18:42 .
All times in EST +10:30 for IST.

Hello all!
I'd like to share my doubts,esp. in Physics,i wud be very grateful if any of u cud answer these,and share u'r doubts too here...
let's have fun with science :)
Well,to start off:
1)According to virial theorem,kinetic energy of a nody is half the potential energy,i.e,if
we take a satellite of mass m and velocity v revolving around a body of mass M,at a
distance R from it then,
Now,when the same theorem is applied to the sun,we say NkT=1/2GM^2/R,where N=avagadro
no.,k=boltzmann constanst,T=absolute temperature,M,R-mass and radius of the sun
respectively.My doubt is,how can the pressure of the gas inside the sun,i.e NkT be
considered as the kinetic energy of the sun?Shouldn't the K.E of the sun be the one by
virtue of it's motion?(just like 1/2mv^2 is the energy associated with the motion of the
2)When we want to calculate the gravitational pressure at the centre of the sun,if we
consider 2 hemispheres of the sun,the force betn. them is given by,(GM/2*M/2)R^2.Where M
and R are the mass and radius of the sun respectively.How can the distance between the two
hemispheres be R?Or is that the distance between their centres og gravity?But even if it
is so,how do we know that the centre of gravity of the hemisphere will be at a depth
exactly 1/2 the radius?Could you also please explain the difference between centres of
mass and gravity?


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