Linear Kinematics

Position: Because kinematics is concerned with motion it would be important to note that motion is defined as a change in position and position is defined as a location in space.  It goes without saying that motion can not be determined without defining a position reference so that magnitude of movement can be quantified. Defining a position reference also avoids confusion.  For example, is a runner 40 m from the start or 60 m from the finish? You must describe position in reference to a fixed position. We defined this positional reference during week 1 (see below).

One important point to be made here is that x and y coordinates may be positive or negative depending on the direction of motion in relation to the reference point (0,0).  The reference point or origin is usually the start or finish of the motion.  Please review the Cartesian coordinate system reported in week 1and the following animation.

 http://www.mhhe.com/physsci/physical/jones/graphics/jones2001phys_s/ch03/others/3-2a/index.html.
  

Please note that for some movements, a position change of only one coordinate (e.g., x) may be needed to quantify kinematics such as a runner’s velocity during a 100 m sprint.