Question

in uniform motion,is it neccsary for the object to travel in a straigt line?

like, why it cant travel in zigzag motion in which it travels the equal path lenths in equal intervals of time. is that uniform motion

Answer 1

This highly depends on the context and is rather a question about nomenclature than physics.
Usually, in elementary kinematics "uniform motion" is defined as motion along a straight path. Uniform motion here means an unchanged state of motion, that is a motion where the velocity remains constant. If the velocity remains the same v⃗ (t)=v⃗ 0v→(t)=v→0, then the path will obviously be the straight line r⃗ (t)=r⃗ 0+tv⃗ 0r→(t)=r→0+tv→0.
The term uniform circular movement is common when discussion the elementary kinematics of rotation, then the path will obviously be a circle.
In more general terms, if you consider motion of an object constrained to a submanifold of space (that means some surface or some arbitrary path), then it would be natural to consider movement along geodesics as uniform motion. This notion coincides with the notion of uniform circular motion given above, if we constrain the object to move on a circle. It also coincides with the notion of a constant velocity: Geodesics are exactly those paths along which the velocity is covariantly constant.