One dimensional motion is motion along a straight line. The line used for this motion is often the familiar x-axis, or x number line. The object may move forward or backward along this line: Forward is usually considered positive movement, and this movement is usually considered to be to the right.
Many introductory physics problems can be simplified to the special case of uniform motion in one dimension with constant acceleration. That is, most problems will involve objects moving in a straight line whose acceleration doesn’t change over time. For such problems, there are five variables that are potentially relevant: the object’s position, x; the object’s initial velocity, ; the object’s final velocity, v; the object’s acceleration, a; and the elapsed time, t. If you know any three of these variables, you can solve for a fourth.