Answer to Question #26654 in Mechanics | Relativity for SAGAR
MOTION IS ALWAYS ALONG STRAIGHT LINE... IF SO THEN WHY EARTH MOVES ALONG AN ELLIPTICAL ORBIT..?
The statement that "motion is always along straight line" is wrong. Motion is a change in position of an object with respect to time and its reference point. It isn't necessary for motion to be linear. In a gravitational two-body problem with negative energy both bodies follow similar elliptic orbits with the same orbital period around their common barycenter. Also the relative position of one body with respect to the other follows an elliptic orbit. That's why Earth follows elliptic orbit.