Earth revollute in Elliptical path but when a stone is tired to a string then it follows circular path not Elliptical path. Why?
Do one thing tie the stone from two strings and and ask your friend to rotate it from your opposite side and see now if it follows elliptical orbit??Find it out yourself???
The Earth does not simply revolve around the sun, it revolves around the common centre of mass of the Earth-Sun system. There is no common centre of mass for a stone tied to a string.
Secondly, the stone moves in a circle because of two forces – the centifugal force due to rotation and tension in the string – being in mutually opposite directions. However, there is no force of tension when the earth-sun system is studied, as gravity is a non contact force.