Different points in the earth are at slightly different distance from the sun and hence experience different force due to gravitation. For a rigid body, we know that if various forces act at various points in it, the resultant motion is as if a net force acts on the `CM` (centre of mass) causing translation and a net torque at the `CM` causing rotation around an axis through the `CM`. for the earth-sun system (approximating the earth as a uniform density sphere).

Options

A. the torque is zero
B. the torque causes the earth to spin
C. the rigid body result is not applicable since the earth is not even approximately a rigid body
D. the torque causes the earth to move around the sun

Answer

B

Explanation

As the earth is revolving around the sun in a circular motion (approxiamately in actual the path of earth around the sun is elliptical) due to gravitational attraction. When we consider the earth sun as a single system and we are taking earth as sphere of uniform density. Then the gravitational force `(vecF)` will be of radiua natur, i..e angle between position vector `vecr` and forec `vecF` is zero, so, torque
`=|vec(tau)|=|vecrxxvecF|=rsin 0^(@)=0`