I had about 50 balloons in my room to dispose of (surprise congratulatory decorations), and I didn't want to go through 50 pops. So I used scissors near the tied end to cut holes large enough that the balloons just shrunk, rather than popping. I noticed a phenomenon though: every time the balloon reached the point that it was no longer stretched taught, it grew suddenly cooler for a little bit.
My first thought was that the air escaping from the balloon took some of the heat with it, in the same way that blowing air over a car engine via the heating system keeps an engine cool. But I realized that made no sense; after sitting around for a few days like they had, the air inside the balloons would certainly have normalized to room temperature, so there was no change.
My next thought was that it had something to do with the decrease in kinetic energy of the balloon as the tension was released. Naturally, as the balloon relaxed it would undergo a change in energy, and that energy would have to go somewhere. But then I realized my mistake; this logic suggests the balloon would grow colder, not warmer.
So long story short, I'm at a loss. Does anybody have a scientific explanation for why balloons grow colder as they shrink? Was I anywhere close, or were my guesses in entirely the wrong ballpark? Thanks!
Note: I noticed that on the four or five balloons I still accidentally popped, the remnants of the balloon were also colder than the original balloon. Not sure if that means anything.
My first thought was that the air escaping from the balloon took some of the heat with it, in the same way that blowing air over a car engine via the heating system keeps an engine cool. But I realized that made no sense; after sitting around for a few days like they had, the air inside the balloons would certainly have normalized to room temperature, so there was no change.
My next thought was that it had something to do with the decrease in kinetic energy of the balloon as the tension was released. Naturally, as the balloon relaxed it would undergo a change in energy, and that energy would have to go somewhere. But then I realized my mistake; this logic suggests the balloon would grow colder, not warmer.
So long story short, I'm at a loss. Does anybody have a scientific explanation for why balloons grow colder as they shrink? Was I anywhere close, or were my guesses in entirely the wrong ballpark? Thanks!
Note: I noticed that on the four or five balloons I still accidentally popped, the remnants of the balloon were also colder than the original balloon. Not sure if that means anything.
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The energy of a system of gas molecules follows a Maxwell-Boltzmann distribution, pictured in the link below. Many particles fall around a median point (the average energy of the system) while a few have greater and lesser energy. When the balloon is deflated, many more of the higher energy particles escape first (due to their tendency to collide more often and travel more quickly), which cuts off the rightmost portion of the distribution. The particles, however, redistribute themselves to follow a similar curve with a lower endpoint and lower average energy.
Since temperature is proportional to the average kinetic energy of a system, the loss of molecules results in a lower temperature.
Since temperature is proportional to the average kinetic energy of a system, the loss of molecules results in a lower temperature.
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I over-thought this answer at first. Heat is a form of energy. Heat can increase the rate at which something reacts, or the rate at which something moves by increasing its kinetic energy. When something is hot, you have molecules moving so much faster that it actually seems as if there are more of them present to reinforce the interior of whatever they're in.