Measurement of Speed

In a car, we see this round thing with a needle-like pointer moving inside.

This is called a speedometer. This is used to measure the speed of the car.

A speedometer needle is pointed towards a number. Here it is showing 80, which means the car is moving with speed 80kmph.

In the middle, you can see one screen that is showing some digits 35758. It is called an odometer.

Odometer is a device used to measure the distance traveled by the car. It means, till now the car has travelled 35758km.

Let’s first understand "speed" and then we will understand how speedometer works.

Speed of a car or any object is the ratio of the distance travelled by it and the time in which it travelled. Speed = distance/time

From this we can say distance = speed X time time = distance/speed. We can remember these using a simple triangle.

Speed has a unit of measurement as m/s - meter/second and km/hr - kilometer/hour(kmph)

Let’s see some examples of finding speed.

1. A bunny has moved 10m forward and then 20 meters backward in 30 seconds. Then what is the speed of the bunny?

Total distance travelled is 10m + 20m = 30m in 30s. So speed is S = D/T = 30/30 = 1m/s.

2. A boy ran from his home to his school with a speed of 3m/s for 60 seconds. What is the distance between his home and school?

From triangle, we can see that distance is D = speed X time Here speed, s = m/s and time taken, t = 60 seconds

From triangle we can see that distance is D = speed X time D = 3 x 60 = 180m so answer is 180m

Let’s see the use of speedometer.

For example, if a car A is showing 0 in its odometer and after 5hrs of travelling it is showing 300.

Then car A has travelled 500km in 5 hrs. Then the speed of the car is 300/5 = 60kmph.

Let’s take another car B. It has travelled same distance 300km in just 3hr.

Then the speed of the car is 300/3 = 100kmph.

So in car A the speedometer will show 60kmph

And in car B the speedometer will show 100kmph.

Revision

Speed of a body is the ratio of the distance travelled and the time taken by the body.

The End