How did the name "two retreats" come from?

The origin of the name of the dipole angle:

Because there are two kinds of sounds after discharge, it is called kicking.

Introduction:

Two-kicking firecrackers are a kind of Han folk products, which are often used in festivals, weddings and other occasions. Every year during the Spring Festival, a salute is often set off, which takes off by the reaction generated by the first primer explosion hitting the ground and explodes in the air. After taking off 10~20 meters, it exploded in the air with a loud sound.

Structural principle:

Erguotou is a kind of firecrackers, and its powder is divided into two layers by cement or soil. The "back door" at the bottom was not blocked tightly, and the airflow generated by the explosion of the lower gunpowder rushed out of the back door and sprayed downward. The downward jet of air generates upward thrust, pushing firecrackers into the air. At this time, the fuse just ignited the gunpowder sealed at the upper end, and it quickly burned-exploded, and the second kick in mid-air blossomed with a bang. Fireworks also rely on the rapid combustion of gunpowder-the thrust generated by the explosion.

At present, the skirting board is mostly an improvement of the original black powder, using potassium perchlorate or barium nitrate as oxidant to realize combustion. Because it is divided into two zones, the lower layer is granular powder, which is characterized by slow burning speed to avoid cracking the paper tube, and the upper layer is mostly powdery explosives mixed with aluminum powder, so the flash effect is more. The bottom layer of the large baseboard is mostly filled with earth, and the paper pipe is wrapped with hemp rope to ensure the stability of the paper pipe and make the explosion sound loud. The back cover of a small machine with two feet is mostly made of paper and spiral.