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# Motion in One Dimension

One of the main concerns of physics is the study of how things move. Ultimately, we can use the same principles we'll study here to understand motion that ranges from apples falling to the ground to planets orbiting the sun. But we'll start out talking about the simplest possible motion, that of an object moving in a straight line.

Position is the term we use to describe the location of an object. In one dimension, there aren't too many choices about how to specify position. Most physicists would choose the letter, x, to represent position and measure in the SI unit of meters. You also need a reference point. For example, in the picture shown here, you could say that the red ball is 2m to the right of the blue ball, or that it is 3m to the left of the yellow ball. Both of those statements are perfectly correct. Usually, a physicist will define a reference frame, which is just an axis with the origin as the reference point, as in the next picture. Then you can just say, the red ball is located at x=1m. To describe motion, we need to have a way to describe how the position of an object changes as a function of time. There are two main ways we do this: graphically and analytically.

Last updated January 26, 2011