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2D Vectors: Pool Ball Displacement, Velocity, and Speed

Experiment #9 from Physics with Video Analysis

Education Level
High School


A careful analysis of two-dimensional motion is more complex than it is for motion in one dimension – especially when calculating velocities and speeds. In this activity, you are going to analyze a movie that shows the 2D motion of a pool ball rolling on a level pool table. The ball starts with its center at point A, moves “up” and to the left to point B, bounces off the edge of the table and rolls “down” and to the left so that its center reaches point C.


In this activity, you will:

  • Scale a movie.
  • Use displacement vectors to find average speed and average velocity.
  • Show that the magnitude of the average velocity, \left| {\left\langle {{{\vec v}_{{\text{A}} \to {\text{C}}}}} \right\rangle } \right|, of object moving in 2D is not always the same as its average speed, \left\langle {{S_{{\text{A}} \to {\text{C}}}}} \right\rangle .

Sensors and Equipment

This experiment features the following sensors and equipment. Additional equipment may be required.

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This experiment is #9 of Physics with Video Analysis. The experiment in the book includes student instructions as well as instructor information for set up, helpful hints, and sample graphs and data.

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