What is Velocity?

A velocity of an object is the rate of change of the object’s position with respect to a frame of reference and time, it might sound complicated but velocity is basically speed in a specific direction. It is a vector quantity, which means we need both magnitude (speed) and direction to define velocity. The SI unit of it is meter per second (ms-1) if there is a change in magnitude or the direction in velocity of a body the body is said to be accelerating.

Speed and Velocity

Speed and velocity can be a little confusing for most of us, Well speed gives us an idea of how fast an object is moving whereas velocity not only tells us its speed but also tells us in which direction the body is moving. We can define speed as a function of distance traveled whereas velocity is a function of displacement. Instantaneous velocity is the velocity of a body at any given time. Average velocity is the total displacement by total time and is given by v = \( \frac {\triangle x}{\triangle t}\) where ∆x is the total displacement of the body and ∆t is the time. Average velocity is always less than or equal to that of average speed; this is because displacement can never be higher than the distance traveled but the distance traveled can be higher than that of displacement.

Example of Velocity

To understand the concept of instantaneous velocity and average velocity let’s take this example. Jewel goes to school in her dad’s car every morning, her school is 8 km from her home and she takes 15 mins to travel, but when she looks at the speedometer on the dashboard of the car it shows different reading all the time now how would she know her velocity?

Well average velocity of jewel’s car could be found by,

For convenience, we have considered the car to move in a straight line and we will convert all the units of time to hour. Therefore 15 mins = \( \frac {15}{60} \)  = 0.25 hours.

average velocity, v = \( \frac {\triangle x}{\triangle t}\)

v = 8km/0.25hrs

v = 32 km/h

Now we see that even though the car may vary its speed if it covers the same amount of distance in the same amount of time every time its average velocity will remain the same.

Differences between Speed and Velocity

Difference between Speed and Velocity
SPEED VELOCITY
Speed is the quantitative measure of how quickly something is moving. Velocity defines the direction of the movement of the body or the object.
Speed is primarily a scalar quantity Velocity is essentially a vector quantity
It is the rate of change of distance It is the rate of change of displacement
Speed of an object moving can never be negative Velocity of a moving object can be zero.
Speed is a prime indicator of the rapidity of the object. Velocity is the prime indicator of the position as well as the rapidity of the object.
It can be defined as the distance covered by an object in unit time. Velocity can be defined as the displacement of the object in unit time.

Let’s summarize what we have learned:

  • (a) This is a function of displacement.
  • (b) We require both magnitude and direction to define velocity.
  • (c) Instantaneous velocity is the velocity at any given moment of time, whereas average velocity is the total displacement divided by total time.
  • (d) A changing velocity indicates acceleration.

I hope you have understood the concept,  for further clarifications about this article and to talk to our experts contact us @byjus.com


Practise This Question

A body is traversing on the x-y plane with constant speed. At the start of the motion, the particles velocity is 40^i and after 30 sec its velocity becomes 40^j. Find the average acceleration.