Justification of Newton's model

[neelakash]

There is a model devised by Newton to predict the difference in the height of the tides (as observed from the earth) due to the attraction of Sun/moon.It is well known.Here we pretend that two tubes,filled up of water runs from the surface to the centre of the earth.They are taken as perpendicular.Hence using npn-inertial frame of the earth,the difference is found.density of water is assumed constant.

To what extent it is justified?What right do we have to assume this superficial model?
All we can say if a model be prepared like this,for it the equilibrium tide-height difference will be ...
Can you please make it clear?

 

[russ_watters]

I'm not following you - "What right"? What does that mean? We believe Newon's model becaus it works. You can derive it from Newton's gravity equation.

 

[neelakash]

My question is why does it work at all?We are simply making a model where there is no resemblance.
I say this because
(1)we are taking two orthogonal tubes of water of equal density!
(2)we are neglecting the non uniform solid core solid core of the earth.