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Position and Displacement
Let's now spend a little time looking at the concepts of position and displacement. In Figure 1 below we see the vector RBA which extends from A to B. As you can see, point B meandered a bit in getting to where it is finally shown. Think of the vector RBA as being stretchy, with point A being fixed and the head of the arrow at point B following along the path as shown.
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Let's now add a coordinate system as shown in (b). We can define position vectors RA and RB which denote of the tail and head of the vector RBA respectively. We can write the following vector equation that describes the relationship between the three vectors: RA + RBA = RB. Rearranging this a bit, we can get the following: RBA = RB - RA. Note that we can create the vector -RA by simply swapping head for tail.
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