Need help about motion So,In my book it is written that -
Translational motion is the motion when all the particles of a moving body move the same distance in the same same in the same direction.It is of two types-1)Rectilinear and 2)Curvilinear
Now, my question is that to have translational motion doesn't need to have uniform velocity,right? Because when a body with fixed mass moves then all of its particles move the same distance in the same time in the same direction. So can't we just say translational motion is  the motion when a body with fixed mass moves from one point to another? doesn't every body experience translational motion when it moves?either in a linear path or curved?
 A: Translational motion is when there is no relative motion between any two particles within the body. When there is any rotational motion of an object about an axis, the particles not on that axis will move perpendicular to their position vector relative to the particles on that axis (circular motion). In case of rolling, there is a combination of rotational and translational motion. So in this case the body is moving from one place to the other, and while there is translational motion, it is not just that.
Also, to your first question: uniform velocity is not necessary at all- if there is some (constant or variable) acceleration of the body, but it is undergoing translational motion, then no matter what the displacement is in any given time, all particles of that body will have the same displacement.
A: 
... all the particles of a moving body move the same distance in the same same in the same direction

So if two points of the body $A$ and $B$ move from positions $A_0$ and $B_0$ to $A_1$ and $B_1$ respectively, this says that
$\vec{A_1}-\vec{A_0} = \vec{B_1}-\vec{B_0}$
which can be rearranged to give
$\vec{B_1}-\vec{A_1} = \vec{B_0}-\vec{A_0}$
In other words, the position of $B$ relative to $A$ at the end of the motion is the same as at the start of the motion. Since this applies to any two points of the body, then translational motion simply means that the body is in the same orientation in space at the end of the motion as it was at the start of the motion - so if you compare the orientations of the body at the start and the end of the motion, there is no rotation. Apart from this, there is no restriction on the path that the body takes or the speed or orientation of the body during the motion.
I think your textbook is giving a rather obscure definition of a very simple concept.
