Question

Any one say me that why earth moves with in a same velocity,and why it never changes its velocity?

Answer 1

It doesn't move with same velocity because it is in an elliptical motion. And velocity involves same direction. And about its speed -it is faster when it is close to the sun and slow when it is away from the sun

Answer 2

Earth doesn't travel with same velocity.

Let's recall that when a body moves in path other than straight line then it does have acceleration.

Similarly , Earth doesn't move in a straight line, it moves in elliptical path. So it has some acceleration. If there is acceleration then there is of course change in velocity.

So, the Earth changes it's velocity always.

Hope This Helps You!