Any time an object is moving, it has some speed. **Speed** measures how fast an object is moving. If an object has speed, it also has a **velocity**, which is simply the vector version of speed. You might want to flip back to Chapter 4, “Vector Operations,” for a quick refresher on the difference between a vector and a scalar quantity. Velocity is speed with a direction. In one dimension, the direction is given by positive or negative. (Chapter 10, “Motion in Two and Three Dimensions,” address how to deal with direction in 2D and 3D.) For now, just consider the motion of an object along a straight line, where positive velocity is forward and negative velocity is backward.

NOTE

The terms “speed” and “velocity” may be used interchangeably ...

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