Please use scientific knowledge to explain: Why does a balloon explode when you prick it with a needle? If you put tape on the balloon and insert a needle into the balloon, the balloon will not burst

Please use scientific knowledge to explain: Why does a balloon explode when you prick it with a needle? If you put tape on the balloon and insert a needle into the balloon, the balloon will not burst.

First of all, you need to understand what happened when the balloon burst?

The above is an animated picture that has been widely circulated on the Internet, which records the moment when an oversized balloon burst. The originally complete balloon membrane instantly turned into many small fragments. It looks very cool, right? But this picture doesn't tell the whole story.

Recently, a study published in PHYSICAL REVIEW LETTERS made a detailed observation of the ruptured balloon film [1]. Researchers pointed out that there are actually two ways for a balloon to burst. One is to crack in a line, and the other is to break into multiple pieces like the above.

What are the factors that affect the way a balloon bursts? In order to figure this out, the researchers designed an experimental device and conducted experiments with latex films of different thicknesses. After blowing air, the membrane inflates to form a "balloon" that is eventually punctured by the spikes on the device. The entire process will be clearly recorded by high-speed cameras, and the researchers will also measure the tension of the balloon membrane.

The results showed that what affected the way the balloon ruptured was the tension of the balloon membrane and the initial thickness of the membrane. When the tension reaches a critical value, the original cracking along a crack will become branched cracking, forming more fragments. Researchers found that the speed of crack opening will increase with tension, and finally reach a limit speed value of 570±15m/s at the critical time (this is almost the speed of sound in latex materials). Above this critical value, the cracking speed cannot continue to increase when the tension continues to increase. At this time, the crack will release energy in the form of multiple crack branches.