why the rocket travels or move in space because space is a vaccum. According to newtons third law action is equal reaction. Rocket travels in atmosphere because it pushes the air and move according to newton. But there is no air in space so how a rocket can travel in space ? [comets travels because of gravity] ?

Actually the principle behind the motion of rocket is not Newtons III law it is actually conservation of linear momentum. When fuel in a rocket burns the gases are released with high speed (opposite to the required motion of rocket). Then rocket moves in a direction opposite to the direction of gases released so that momentum is conserved. Hence atmosphere is not required for the motion of rocket.

But in proving the conservatoin principle we use Newtons III law.So sometimes it is said that Newtons III law is the working pringiple behind motion of rocket.

More precisely it is conservation of liner momentum.

If you are satisfied with my answer pls approve this.

But here newtons third law is also applied !

But here newtons third law is also applied !

But here newtons third law is also applied !

But here newtons third law is also applied !

But here newtons third law is also applied !

Here Newtons law is not violated .Hence Newtons law can be applied.

A rocket is not propelled by pushing the surrounding air backwards but by ejection of a portion of its mass to the back.The forward force on the rocket is the reaction to the backward force on the ejected material and as more material is ejected the mass of rocket decreases.