Velocity, Average Velocity and Instantaneous Velocity

Introduction

In physics, it is not enough to know how fast an object is moving; we also need to know the direction of motion. This concept is known as velocity. In this topic, we will study velocity, average velocity, and instantaneous velocity along with their formulas.

Definition of Velocity

Velocity is defined as the displacement travelled by an object per unit time in a given direction.

It tells us both the speed and the direction of motion.

Formula: Velocity = Displacement / Time

Unit: SI unit of velocity is metre per second (m/s).

Example of Velocity: A car moves 80 m towards east in 20 s.

Velocity = 80 / 20 = 4 m/s towards east

Illustration of Velocity:

Start End Displacement = 80 m East Time = 20 s

Average Velocity

Average velocity is defined as the net displacement divided by the total time taken.

Here, net displacement means the overall change in position of the object from initial point to final point, including direction.

Formula: Average Velocity = Net Displacement / Total Time

Average velocity depends on net displacement, not on total distance travelled.

Example of Average Velocity:

A person walks 60 m towards east in 10 s and then returns 40 m towards west in 20 s.

Net Displacement = 60 m - 40 m = 20 m towards east

Total Time = 10 s + 20 s = 30 s

Average Velocity = 20 / 30 = 0.67 m/s towards east

Illustration of Average Velocity:

Start Turn End 60 m East 40 m West Net Displacement = 20 m East 10 s 20 s

Instantaneous Velocity

Instantaneous velocity is the velocity of an object at a particular instant of time.

It gives both magnitude and direction at that instant.

For example, the velocity of a car at a particular moment (with direction) is its instantaneous velocity.

Illustration of Instantaneous Velocity:

At this instant Velocity = 15 m/s East Particular moment of motion

Examples from Daily Life

  • A car moving with a speed of 20 m/s towards east has a velocity of 20 m/s east.
  • If a person walks from home to a shop and then returns back to home, the net displacement is zero, so the average velocity is zero.
  • A train moving in a straight line with constant direction has constant velocity.
  • When a vehicle changes its direction, its velocity changes even if its speed remains the same.

Important Points

  • Velocity is a vector quantity because it has both magnitude and direction.
  • It can be positive, negative, or zero depending on direction.
  • Average velocity depends on net displacement, not on total distance.
  • Instantaneous velocity is measured at a specific instant.

Conclusion

Velocity is an important concept that describes motion with direction. Average velocity gives the overall change in position over time, while instantaneous velocity gives the exact velocity at a particular moment. Understanding velocity helps in analyzing real-life motion more accurately.

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