In thunderstorm weather, we often see lightning first and then hear thunder. Do you know why?

Lightning and thunder occur at the same time, but their propagation speeds in the atmosphere are quite different. Light can travel 300 thousand kilometers per second, while sound can only travel 340 meters, so people always see lightning first and then hear thunder.

According to this phenomenon, the distance between seeing lightning and hearing thunder can be calculated. If lightning is in the northwest and thunder is heard every 10 second, it means that the thunderstorm is about 3400 meters.

Extended data:

In summer, when cumulonimbus clouds are formed in the sky, water droplets or ice crystals in the cloud droplets collide with each other due to the intense airflow movement, which makes the cloud droplets split or merge continuously and carry positive or negative charges at the same time. With the continuous ups and downs of the airflow, the clouds formed by the cloud drops are getting bigger and bigger, and more and more charges are accumulated.

A strong electric field is formed between two clouds with a large number of opposite charges, or between a charged cloud and the earth. The closer the distance between clouds or between clouds and the earth, the stronger the electric field. When the high voltage (up to several billion volts) generated by the electric field breaks through the atmosphere (up to hundreds of thousands of amperes), a fierce spark discharge (energy up to 10 14 Joule) will be generated between two clouds or between clouds and the earth.

Bright electric sparks cut across the sky, that is, people see lightning (about one millionth of a second to one hundredth of a second). The discharge causes strong vibration of the air and makes great noise. This is the thunder that people hear.

China academy of sciences popularization of science cloud platform-thunder and lightning