A moving body changes its position with time. In order to measure the rate of such change, two physical quantities are interchangeably used. These are nothing but speed and velocity. Although both has same unit of measurement, they are different in many aspects. Speed of a moving body is defined as the rate of change of distance; whereas, velocity is defined as the rate of change of displacement. Since distance (and time also) is a scalar quantity, so speed is also a scalar quantity. On the other hand, displacement has a specific direction along with its magnitude, so displacement is a vector quantity and hence velocity is also vector. Similarities and differences between speed and velocity are elaborated in the following sections.

Similarities between speed and velocity

• Both are physical quantities, so both can be measured and quantified.
• Both the terms (speed and velocity) are associated with moving body only; not with static body.
• Both have same unit of measurement—m/s in SI and cm/s in CGS. Dimension is also same for both the physical quantities, which is [L T^–1].
• Both could be either uniform or non-uniform; that means uniform speed, uniform velocity, non-uniform speed and non-uniform velocity—all are possible.

Differences between speed and velocity

Speed	Velocity
Distance traveled by a moving body per unit time is called speed.	Distance traveled by a moving body per unit time in a particular direction is called velocity.
Speed is a scalar quantity. So it has only magnitude but no specific direction.	Velocity is vector quantity. So it has both magnitude and direction.
Average speed of a moving body can never be zero.	Average velocity of a moving body can be zero because of the algebraic summation.
Speed of a moving body can never be negative. It always has a finite positive value.	Velocity of a moving body can be negative based on the measured direction.
A moving body having uniform velocity must have uniform speed.	A moving body having uniform speed may not necessarily have uniform velocity.
Speed of a body cannot be resolved; in fact, it always has same value irrespective of measured direction.	Velocity of a body can be resolved in two mutually perpendicular directions using sine or cosine of adjacent angle.
While specifying speed of a body, only value with unit is sufficient.	While specifying velocity of body, the direction must be specified along with the value and unit.