Position & Displacement Vectors (DP IB Analysis & Approaches (AA)): Revision Note

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Position Vectors

What is a position vector?

  • A position vector describes the position of a point in relation to the origin

  • The position vector of point A is written with the notation bold italic a equals OA with rightwards arrow on top 

    • The origin is always denoted O

  • The individual components of a position vector are the coordinates of the point

    • For example, the point with coordinates (3, -2, -1) has position vector 3 bold italic i – 2 bold italic j – bold italic k

Worked Example

Determine the position vector of the point with coordinates (4, -1, 8).

3-9-2-ib-aa-hl-position-vector-we-solution

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Displacement Vectors

What is a displacement vector?

  • A displacement vector describes the shortest route between any two points

  • The displacement vector of point B from the point A is written with the notation AB with rightwards arrow on top

  • A position vector is a displacement vector of a point from the origin

  • A displacement vector between two points can be written in terms of the displacement vectors using a third point

    • For example, AB with rightwards arrow on top equals AC with rightwards arrow on top plus CB with rightwards arrow on top

  • A displacement vector can be written in terms of its position vectors

    •  For example, AB with rightwards arrow on top can be written in terms of OA with rightwards arrow on top and OB with rightwards arrow on top

      • AB with rightwards arrow on top equals AO with rightwards arrow on top plus stack OB blank with rightwards arrow on top

      • This can be rewritten as AB with rightwards arrow on top equals OB with rightwards arrow on top minus stack OA blank with rightwards arrow on top  

Diagram showing vectors in a triangle. OA is vector a, OB is vector b. AB is displacement vector b-a. Text explains vector relationships.
Example of a displacement vector in terms of position vectors

Worked Example

The point A has coordinates (3, 0, -1) and the point B has coordinates (-2, -5, 7). Find the displacement vector AB with rightwards arrow on top.

3-9-2-vectors-we-solution-position-and-displacement-wqe-solution

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