# It is difficult to initially blow a baloon,but becomes easier as it expands,why it is so?

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its harder when you start because the balloon is starting to strech,

and when you start, your cheeks are streching so thats why its harder

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• Anonymous

the difficultly to blow the balloon depends on the excess pressure (excess pressure = pressure that is excess of the already present atmospheric pressure outside) needed to inflate it. excess pressure inside the balloon depends on two factors. 1.tension of the rubber and 2.the radius of curvature of the balloon(assuming it is spherical).

as rubber is stretched its tension increases(the argument given in an earlier answer that density decreases and hence tension decreases is wrong; if that be the case then it would become more easier as you stretch a rubber band longer). so this factor should make blowing more difficult when balloon expands.

but the radius of curvature has the opposite effect. smaller the radius higher the pressure. this factor more than compensates the first one. so blowing is difficult initially when radius is small.

you can read the following article where they have given the mathematical formula for excess pressure

http://web.mit.edu/nnf/education/wettability/bubbl...

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• Initially the material is denser and hence the surface tension is higher, which reduces when the baloon is blown and the material becomes thinner.

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• it is harder to begin with because the baloon has no defined shape, therefore the air is just being forced in but not sorted, where as after it is started, all of the airflow is in equal portions, so it sorts itself and expandt the baloon, or something.

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