How to tear only one opening of the tinfoil paper in the cigarette box:

Tear off the tinfoil on the sealing side of the cigarette box. Hold the cigarette box in your left hand and tap it with a finger on your right hand. The smoke will come out.

Under mechanical analysis, the cigarette on the other side of the opening receives gravity and static friction in the vertical direction, and the force is balanced and stationary. At the moment of knocking, according to the impulse theorem, the instantaneous force on the cigarette box is very large. is large, resulting in a large acceleration. If the cigarette on the other side of the opening wants to remain stationary with the cigarette box, it must reach the same acceleration as the cigarette box. It is generated by the combined force of static friction and gravity. But the static friction has a maximum value. When the maximum static friction When the force plus the force reaches the point where the cigarette cannot produce the same acceleration as the cigarette box, the cigarette will be displaced relative to the cigarette box, and the cigarette will come out.