Why are balloons harder to inflate when you start, and feel easier once they start expanding?

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I mean your average party balloon, when it’s completely deflated, it seems you have to put extra effort into getting it going. As soon as it starts inflating, you need less effort.

In: Physics

28 Answers

Anonymous 0 Comments

It has to do with elasticity. I dont know the science behind it but you have to overcome the inertia of the elastic material. Its like a nice brand new pair of pants with an elastic waist band or a rubber band. They fit nice when they are new but over time as you stretch the elastic material it no longer fits nice. There is also a breaking/degradation (not sure if this is the correct words) point of elastic material. Maybe is denaturing but my point is you can inflate a balloon to the point where it wont go back to its original shape.

Anonymous 0 Comments

When you first start blowing, the thickness of the balloon wall is really thick and resists stretching. But as the balloon gets bigger, the wall is thinner and thinner and easier to stretch.

Anonymous 0 Comments

Imagine 2 circles made of string. One is larger than the other. When you cut the strings as expected the larger circle is made of a longer string. Now when you inflate the balloon you are applying a constant force along the entire length of that string. So if you had a string that is 6 inches and you put one pound of force per inch you are at 6 lbs of force. Well that force causes the circumference to increase meaning your string is getting longer. Now you continue to add air at 1 pound per inch only now your string is 8 inches long. That means over the entire length of the string you are now applying 8lbs of force instead of six. The problem is now it takes more air to stretch the balloon because of this increase in volume. But luckily it has become easier so as long as you have time you can Basically make the balloon as big as the material will allow.

Anonymous 0 Comments

I’m just an Electrical Engineer who had a lot of early-career exposure to material science and mechanical engineering stuff, but I’m pretty sure it’s just a stress/strain thing that applies to all materials, even nonlinear materials like polymers, right? don’t all materials have plastic and elastic regions of their stress vs. strain curves?

I used to work on high strength cables that were towed behind navy ships or laid on the bottom of the ocean, and they’d have really high axial tension strengths like 45klbf (thousand pounds-force), 100klbf, one was even a half million pounds axial tension strength. I used to get to be involved in pulling them to failure, which was like a bomb going off.

Anyway, just like with balloons, these cables, or more specifically the steel strength members in them, wouldn’t budge through tens of thousands of pounds on tension. We knew it was going to break though as we watched the elongation. At first, they wouldn’t stretch more than a few inches over a 50-foot length. As we approached the ultimate tensile strength though, suddenly the elongation would rapidly increase: as the steel transitioned from its elastic to plastic region, applying a constant or increasing force would stretch it more and more, and within a few seconds it would break. The stored energy released in microseconds, the cable would literally explode when the steel strength members finally gave way.

Anonymous 0 Comments

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Anonymous 0 Comments

Since there’s nothing stretching the balloon, it’s at its thickest point, which means that you have to stretch it out first. Once it is stretched out, it’s easier to stretch it bit by bit. When there’s air in the balloon already, adding more air is easier because the balloon is still being stretched out by the air you put in at the start.

Anonymous 0 Comments

When it is deflated you have the least amount of surface area in the balloon to apply pressure to with your lungs.

As it inflates, it is creating MORE surface area but that SAME small entry point (from the nozzle) will require less applied pressure to stretch the entire balloon.

So a deflated balloon is the smallest surface area we can apply pressure to, which means the force required to inflate it would be the highest.

Heat also helps with elasticity (but not too much!!). This, combined with a little bit of “elastic memory” is why you can struggle to blow up a balloon, but once you get a lungful or two in, you can deflate it and do it again more easily.

Anonymous 0 Comments

When balloon small, need big push to make big
When balloon big, need small push to make bigger
Small balloon strong
Big balloon stretchy

Anonymous 0 Comments

If the deflated balloon has one square inch of surface area and you put one pound per square inch (psi) into it, there is one pound of force trying to stretch the balloon. If the balloon has 10 square inches of surface area and you put one psi into it, there are 10 pounds of force stretching the balloon.

Anonymous 0 Comments

I assume that after the first couple of breaths the energy in the rubber atoms is higher from the friction caused by expansion, allowing easier further expansion