Which statement best differentiates velocity from speed?

• A. Velocity includes direction; speed is magnitude only.
• B. Speed includes direction; velocity is only magnitude.
• C. Velocity is always greater than speed.
• D. Speed is a vector quantity.

Answer: (A)

The key idea is that velocity is a vector quantity: it tells you how fast something is moving and in what direction. Speed is a scalar quantity: it only tells you how fast, with no regard to direction. So the statement that best differentiates them is that velocity includes direction while speed is magnitude only. For example, a car traveling at 60 mph north has a velocity of 60 mph toward the north; if it travels the same 60 mph but south, its speed is still 60 mph, but its velocity is 60 mph toward the south. Velocity can be described with direction, while speed cannot. It isn’t correct to say velocity is always greater than speed, since velocity and speed share the same magnitude but velocity also includes direction; they aren’t ordered quantities. And speed isn’t a vector because it has no direction.