Speed, Average Speed and Instantaneous Speed

Introduction

In our daily life, we often talk about how fast an object is moving. This concept is known as speed. In physics, speed helps us understand the rate at which an object covers distance. In this topic, we will study speed, average speed, and instantaneous speed along with their formulas.

Definition of Speed

Speed is defined as the distance travelled by an object per unit time.

It tells us how fast an object is moving.

Formula: Speed = Distance / Time

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

Example of Speed: A car travels 100 m in 20 s.

Speed = 100 / 20 = 5 m/s

Illustration of Speed:

Start End Distance = 100 m Time = 20 s

Average Speed

Average speed is defined as the total distance travelled divided by the total time taken.

It is used when an object does not move with constant speed.

Formula: Average Speed = Total Distance / Total Time

Average speed gives an overall idea of motion during the entire journey.

Example of Average Speed: A car travels 60 m in 10 s and then 40 m in 20 s.

Total Distance = 60 m + 40 m = 100 m

Total Time = 10 s + 20 s = 30 s

Average Speed = 100 / 30 = 3.33 m/s

Illustration of Average Speed:

Start Mid End 60 m 40 m 10 s 20 s

Instantaneous Speed

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

It tells us how fast an object is moving at a specific moment.

For example, the speed shown by a speedometer in a car at any instant is the instantaneous speed.

Illustration of Instantaneous Speed:

0 20 60 Speedometer Reading = 50 km/h This is the instantaneous speed at that moment.

Examples from Daily Life

  • A car travelling 60 km in 1 hour has a speed of 60 km/h.
  • If a person travels different distances in different intervals of time, average speed is calculated using total distance and total time.
  • The reading of a speedometer at a particular moment gives the instantaneous speed.

Important Points

  • Speed is a scalar quantity because it has only magnitude and no direction.
  • Speed is always positive.
  • Average speed is based on total distance and total time.
  • Instantaneous speed is measured at a particular instant of time.

Conclusion

Speed is an important concept in physics that helps us understand motion. Average speed gives the overall rate of motion, while instantaneous speed gives the exact speed at a particular moment. Both are useful in describing the motion of objects in different situations.

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