Why is the pressure lower in the larger balloon?
There are two effects which cause this. The first is connected to the shape of the balloon. The small balloon is more curved so more of the tension in the rubber is compressing the gas, so for the same tension there will be a higher pressure in a smaller balloon. This is why blowing up long thin balloons is so difficult, the bit at the end is very curved so the pressure is very high.
If you think of a little bit of rubber and the direction that the tension is pulling in, on a curved piece of rubber the tension is pulling the rubber downwards compressing the gas, but on a less curved piece the rubber is mostly pulling against other rubber and not squashing the gas inside.
A curved surface
A straigher piece of balloon
If the balloon is small then it is very curved so quite a lot of the force is compressing the gas in the balloon.
If it is larger then much less of the tension in the rubber is directed to squashing the gas.
The other effect is a peculiarity of rubber. if you stretch a rubber band, it starts off stiff, then gets more stretchy and then goes very stiff again, If you half inflate a balloon it is just starting to get more stretchy. So if one balloon is slightly smaller than the other the rubber will be stiffer on the smaller balloon making the pressure even higher.
If you try and do the same experiment with fully inflated balloons it won't work because they will both get stiffer as you stretch them so the larger balloon will be at a higher pressure and air will flow to cancel out any differences.
Why is the pressure lower in the larger balloon?There are two effects which cause this. The first is connected to the shape of the balloon. The small balloon is more curved so more of the tension in the rubber is compressing the gas, so for the same tension there will be a higher pressure in a smaller balloon. This is why blowing up long thin balloons is so difficult, the bit at the end is very curved so the pressure is very high.If you think of a little bit of rubber and the direction that the tension is pulling in, on a curved piece of rubber the tension is pulling the rubber downwards compressing the gas, but on a less curved piece the rubber is mostly pulling against other rubber and not squashing the gas inside.A curved surfaceA straigher piece of balloonIf the balloon is small then it is very curved so quite a lot of the force is compressing the gas in the balloon.If it is larger then much less of the tension in the rubber is directed to squashing the gas.The other effect is a peculiarity of rubber. if you stretch a rubber band, it starts off stiff, then gets more stretchy and then goes very stiff again, If you half inflate a balloon it is just starting to get more stretchy. So if one balloon is slightly smaller than the other the rubber will be stiffer on the smaller balloon making the pressure even higher.If you try and do the same experiment with fully inflated balloons it won't work because they will both get stiffer as you stretch them so the larger balloon will be at a higher pressure and air will flow to cancel out any differences.
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