Why does air escape through a pinched ballon?

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When a balloon is pinched, the air escapes because the elasticity of the balloon's material creates internal pressure that exceeds atmospheric pressure. The balloon's rubber stretches and, when pinched, reduces its volume, causing the internal pressure to rise and push air out. Contrary to the belief that internal and external pressures are equal, the internal pressure must be higher to counteract both atmospheric pressure and the tension from the balloon's surface. This phenomenon is influenced by the type of balloon and its material properties. Ultimately, the escape of air is a result of the balance between internal pressure and the forces exerted by the balloon's elasticity.
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Hello guys,

This is simple question but I have gone completely blank. Ok let's say there was a balloon outside that was inflated. This means that it has expandes so it's pressure is equivalent to atmpospheric pressure right?

So when I pinch it why does air escape, how does balloon suddenly have higher pressure to make air move out? Is pinching the balloon equivalent to making the volume of the balloon smaller. Thanks :smile:
 
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I believe the answer to this question isn't about the atmospheric pressure, but about the force that the elasticity of the rubber of the balloon has on the air. What happens when you stretch the rubber and let it go? It returns back to its original shape right? The same thing in this case. The expansion of the rubber is just stretching it, so when it has the opportunity, the balloon will go back to its original shape and size, thus pushing out the air.
 
The answer to this question is all about pressure. The pressure inside a balloon is not equal to the atmospheric pressure. In particular,
sameeralord said:
Ok let's say there was a balloon outside that was inflated. This means that it has expandes so it's pressure is equivalent to atmpospheric pressure right?
This is not correct.
 
I have heard the same thing before (pressure inside a balloon= pressure outside), from a physics teacher or something like this...so I'm not surprised that OP is asking this question. I was wondering the same thing.

I think I resolved it to myself by dismissing what the physics teacher said as BS, though. Sure the balloon expanded, but the expanded balloon is nevertheless pressing on the air inside of it, so surely the pressure must be higher.
 
Lsos said:
I have heard the same thing before (pressure inside a balloon= pressure outside), from a physics teacher or something like this...so I'm not surprised that OP is asking this question. I was wondering the same thing.

I think I resolved it to myself by dismissing what the physics teacher said as BS, though. Sure the balloon expanded, but the expanded balloon is nevertheless pressing on the air inside of it, so surely the pressure must be higher.

Yup .. the internal pressure must be higher to balance both the external pressure + the "surface pressure" from the elastic material of the balloon. This latter term is directly proportional to the surface tension, and inversely proportional to the radius (assuming a spherical shape).
 
If you took a deflated balloon up into space (assume ambient pressure is zero). Let a small amount of air into the balloon. It will inflate until the pressure balances. It could well burst if you put 'too much' air in but, if it settles down, the pressure inside will be finite and the pressure outside will be zero. The pressure inside is due, entirely, to the forces of tension in the balloon membrane.
 
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