eli5: My 5-year-old wants to know why some balloons are so loud when they pop.

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My answer was “because of the air…”

In: 4

An intact balloon contains air, air that’s at a higher pressure than the atmosphere around it. When the balloon pops and the barrier between high pressure and low pressure is suddenly gone, you get a pressure difference. That’s what sound is

TLDR: The air inside the balloon rushes out so fast that it makes the popping sound.

Sound is nothing more than the vibration of the air.

When you pop a balloon, the elastic latex of the balloon shrinks back to it’s original size in a few milliseconds.

All the compressed air inside the balloon then creates a pressure wave that expands outwards. We hear that pressure wave as a *POP*

Balloons are full of compressed air. Sound is a wave in air. As a balloon pops, the air rushing out creates a wave that your ear picks up.

Tires are also just very strong balloons, so they [pop even more impressively](https://www.youtube.com/watch?v=HANwJp8Z5mc)

Sound is made by vibrations that cause pressure waves in the air. Think about what happens when you poke your finger in water. It makes waves, right? That’s similar to a quiet sound in air. Now imagine you drop a big rock into the water. You get bigger waves, right? Stuff that “pushes” harder on the air and makes bigger “waves” makes louder noises.

Now, think about a rubber band, since that’s something similar to a balloon. If you pull it just a little bit, then let it go on one end and have it hit your arm, how’s that feel? Probably not too bad. Now imagine stretching it as far as it can go without breaking before letting it snap onto your skin. That’d feel worse and probably hurt, right? The more we make it “spring”, the harder it hits stuff.

A balloon has air inside of it. That air has been PUSHED into the balloon, so it has what we call “pressure”. The reason the balloon got bigger is that pressure stretched the rubber. When you pop the balloon, you create a small tear in the rubber. The air pushes on that torn area, and because it’s torn it can’t push back against the air and the tear gets bigger. As air escapes, there is less pressure, and the rubber starts to “unstretch”.

The balloons that don’t pop so loud either are less inflated (so the rubber isn’t as tight), are made of a material that’s not as “springy”, or are maybe older and have lost some “springiness”. So when they pop, the whole process of the balloon tearing and air escaping is a little slower and it’s more like the rubber band we didn’t pull back very far. That means it “pushes” on air less and makes less dramatic waves, so we don’t hear as loud of a noise.

The balloons that are louder were more inflated and maybe made of a “stretchier” rubber. So when you popped them, the process of the balloon tearing and deflating happened much faster, which makes bigger waves, so you hear a louder noise.

Some balloons are louder than others because either they’re at higher pressure or they’re louder. As others said, the energy stored in the compressed gas turns into sound waves at the pop.

The loudest balloon pop I’ve heard was a balloon filled with acetylene. The pop was done with a torch and was proceeded by an explosion that made my ears ring for a day.