VELOCITY

Linear Velocity is the measure of the linear (straight-line) distance something moves in a specified amount of time. It is typically calculated as distance divided by time, and has units such as feet-per-second, miles-per-hour, and furlongs-per-fortnight.

Velocity, in a strict definition, is a vector quantity, meaning that it has both magnitude and direction. Technically, "speed" is the magnitude portion of a velocity. However, velocity is sometimes given in terms of magnitude only, and in many of those cases, the direction is irrelevant. In others, the direction is self-evident.

Angular velocity is the measure of rotational distance something moves in a specified amount of time. It is typically expressed in units such as revolutions-per-minute (RPM) and degrees-per-second.

For many engineering calculations, it is necessary to express angular velocity in units of radians-per-second, rather than degrees-per-second or RPM. (The explanation of "why" requires more math than is appropriate here, but suffice it to say it is necessary in order to make the numbers work out right).

A radian is an angular measurement equal to approximately 57.3 degrees. It is defined as the angle formed by an arc on the circumference of a circle, the length of which is equal to the radius of that circle. Since the circumference of a circle is the radius times 2π, then obviously the value of a radian is the angle 360° divided by 2π, or 57.29578 degrees.