What happens to these balloons when you open the valve?
A demonstration shows that when a valve opens between a large and small balloon, the large balloon gets bigger while the small one gets smaller—counterintuitively because the smaller balloon actually has higher pressure. This occurs because polymer chains in rubber are tangled when the balloon is small and unexpanded, making it stiffer, but relax as the balloon inflates, resulting in lower pressure in larger balloons.
Summary
The video presents an experiment testing predictions about air pressure dynamics between two connected balloons of different sizes. Multiple observers make initial predictions: some expect the balloons to swap sizes, others predict nothing will happen, and some correctly hypothesize that air will flow from high to low pressure. When the valve opens, the result surprises most viewers—the big balloon becomes even bigger while the small balloon shrinks. The explanation reveals a counterintuitive principle: smaller balloons maintain higher internal pressure than larger ones because the rubber polymer chains are tightly tangled when the balloon is small, creating greater stiffness. As a balloon inflates, these polymer chains gradually uncoil and relax, which paradoxically reduces the pressure inside despite the increased volume. The presenter relates this to common experience: people often notice that blowing up a balloon requires more effort at the beginning but becomes progressively easier as the balloon expands. This physical principle explains why pressure decreases as balloon size increases, contrary to most intuitive expectations about pressure relationships.
Key Insights
- When a valve between two balloons opens, the larger balloon gets bigger because the smaller balloon actually maintains higher pressure due to its compressed polymer chains
- Smaller balloons are stiffer because polymer chains inside the rubber are tangled up tight, which creates higher pressure resistance
- As a balloon inflates, polymer chains uncoil and relax, which means larger balloons operate at lower pressure than smaller ones
- The difficulty of blowing up a balloon decreases as inflation progresses because the polymer chains relax and require less pressure to expand
- This pressure inversion between balloon sizes is counterintuitive and not obvious to most people despite being observable in everyday balloon inflation
Topics
Transcript
[0:00] I've got a big balloon and a small balloon separated by a valve. What happens when I open it? How is that air going to flow? What's going to happen to the big balloon? What's going to happen to the small balloon? >> Um Um >> I think they may be swap sizes. >> I think nothing's going to >> atmospheric pressure, I think nothing will happen. >> Nothing's going to happen? >> This one is going to get bigger because I feel like this one's already like too full with air. >> Maybe this one will pull air inside that one. >> Probably the air is going to push from this one to the smaller one cuz there's…
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