# Activity 8.7 Class 9 Science Chapter 8 Motion

Activity 8.7 Class 9 Science Chapter 8 Motion

Activity 8.5 asks us to know why there is a gap between thunder and lightning. The question also asks us to calculate the distance of lightning.

#### The gap between thunder and lightning

Friction between two clouds results in thunder and lightning. Both the process happens simultaneously, but the speed of light is very high i.e. 300,000km/sec; while that of sound in air is 346m/sec. As a result, we see the lightning almost instantaneously, while it takes time for thunder sound to come near our ears.

#### How can we measure the distance of nearby lightning

We can calculate the gap between the lightning and thunder sound. Lightening is almost instantaneous. It will mark as start for the journey of sound. The gap is the time taken to travel and come near our ears.

With the velocity of sound given, we can calculate the distance by the following way:

Let us take the time gap between thunder and the lightning is 6 sec.

Distance = speed x time

= 346 X 6

= 2076meter.

Note:

The time gap depends on the distance between the ground and the cloud. So, in hilly areas with high altitude time gap can be very less (can be less than one sec in the Himalayan hills).