Please be gentle. I am not that smart.
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The pressure inside a balloon has an inverse relationship with the thickness of the balloon in its inflated state.
This is why getting the first puff into a balloon is by far the hardest. As you inflate it more and more the thickness of the rubber decreases so its ability to compress the air to a higher pressure also decreases.
In the two balloon example you mention the smaller balloon is closer to the state where you have to put a lot of effort into initially inflating it, so the air pressure is higher, so when you open the valve the air flows from the higher pressure zone to the lower pressure one.
In a lot of systems the more you put in the harder it is to put the next little bit in. We might imagine filling a jar through a port at the bottom: the more water is in the jar the more pressure we have to overcome to keep putting water in.
In those sorts of systems if we set up this kind of problem we’d get the intuitive result. The fuller side is trying to push its contents out harder than the empty side, so material flows until the forces are equalized. This won’t necessarily happen when there’s an equal *volume*, but if they reach an equal *pressure* then everything will stabilize.
Balloons have a backwards relationship between pressure and volume, though. The hardest bit of air to get into a balloon is the first little bit that gets the rubber to stretch. From there it gets easier and easier to put more and more air in–up until right around the time it pops (balloons are grossly non-linear and really a pain to try to characterize mathematically).
So when you have less inflated balloon it’s trying harder to push its air out than a more inflated balloon is. Hook them together and the less inflated balloon will win the contest, pushing its air into the more inflated balloon.
A balloon can push the air away harder if it is still smaller. Generally speaking, pressures will equalize, but there might be some sweet spot, a specific configuration where indeed, the air from the bigger balloon may stay there, but that would be because the big balloon cannot push hard enough to inflate the small balloon.
Simply explained:
Try blowing up balloon.. it is harder from the start then when it is slightly expanded..
Why?
If you blow 1cm³ into empty balloon, it gets stretched way more then if you blow 1cm³ into half full one.
It’s hard to imagine, but air inside is under smaller pressure when the balloon is half full, than when it’s empty
When the valve opens, the air flows towards less pressure. If we assume that pressure in the bigger balloon is higher than that of the smaller balloon, the air flows towards the smaller balloon.
However, in this case, it is assumed that pressure in the smaller balloon is higher, so air flows from the small balloon to the big balloon. Airflow continues as long as the pressure is higher in the small balloon. In the end, the balloons have the same pressure, and this means that neither of the balls are totally empty (unless they were empty at the beginning).
There was literally a Vsauce video about this just 2 weeks ago. It’s already explained in simple terms.
The smaller balloon is exerting more pressure and harder to inflate therefore it’s pushing back on the larger inflated balloon harder.
Whty do you ask this is Vsauce explains it in the same video you got this question from?
What will happen if you have 100 balloons each with a valve. And you open all valves at the same time?
VSauce actually did a video on this recently: https://youtube.com/shorts/B_pDZi0kxKw?si=Y4E4eMo1w9fcGylF
Because you’re not just dealing with two, static yet differently sized containers. The latex of the balloons themselves are under tension, and trying to squeeze themselves back down to their normal size. They are both squeezing down with equal force (assuming the same material, etc), but since the more inflated balloon is applying that pressure over a larger area, it loses to the smaller balloon’s squeezing force.
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