Sometimes people use the words, speed and velocity exactly as synonyms. People are confused a lot about how to use the words, speed and velocity and in which context the exact word can fit in. In normal language the speed is a more popular word to display, the faster movement of an item while the word velocity has more significance in physics branch of science. However, it does not restrict the term speed to be limited in the general sense and cannot be used in Physics. Both these words have totally different meanings in the context of application in physics. In general, we can say that speed is a scalar quantity and velocity is a vector quantity.
Physical Interpretation of Speed and Velocity
The quantity which requires the knowledge of both magnitude and direction is called a vector quantity. The quantity which does not require the knowledge of direction is called a scalar quantity. While studying about velocity the knowledge of magnitude and direction is necessary. For an instance, let us talk about a biker riding with a speed of 30km/hour. The speed of the bike is constant no matter in which direction it moves. If the same bike is travelling with a 30km / hour in the north we can say that the velocity of the bike is 30km/hour in the north.
Velocity plays an important role in physics. With the knowledge of required velocity machines can be designed easily. Speed is purely the concept of magnitude, it never requires the direction because it doesn’t matter in which direction the speed is the magnitude always remains constant.
Standard Units of Speed and Velocity
The standard unit of speed is derived by simple formula distance/time that means the unit of speed can be meter/second and kilometer/hour. In the similar manner the unit of velocity can be derived the formula for velocity is also distance/time. So the units are the same as speed, but direction has to be specified for example 90km/hour in the west.
Hence, one can conclude that in case when the direction is also important to mention, one can use the word velocity otherwise in general sense speed is a perfect term to be used.