In such motion the position given by only one of the three Cartesian co-ordinates i.e., x or y or z changes with time, e.g.,
(i) A fruit falling from a tree.
(ii) A train running on a straight railway line.
(iii) A car running on a narrow straight road etc. In the given figure a particle moves from origin along x −axis so its co-ordinate changes from O to x1.
