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

Think of the forces on a small piece of the balloon rubber. There is tension around the outside from the elasticity of the balloon material. Because of the curvature of the balloon, some of that elastic tension is pulling that piece of rubber inward. This force is countered by the pressure difference providing an outward force. If the balloon wall is in equilibrium, those forces should all cancel out. If you blow air into the balloon the pressure increases, and if the balloon expands the pressure decreases, so one way to think of it is that the balloon will change its size until the equilibrium state is reached.

Now, consider that the bigger a balloon is, the less curved any small segment of it will be. Even if the balloon material gets tighter as the balloon stretches, less of that tension is directed inward, meaning that less pressure is needed in the balloon to maintain equilibrium. When you blow up a balloon, your lungs are working against the pressure inside the balloon.

Overall, this means bigger balloon leads to less pressure needed to balance the tension of the balloon, which leads to less work your lungs have to do to blow it up.

Anonymous 0 Comments

When you start blowing up the baloon, the rubber its made of is stiff and thick (compared to what happens next). When you blow air into it, you can feel that it quickly stretches a lot, and then it gets easier to blow it up completely. That is also why its much easier to blow up a baloon which was once filled with air and deflated.

Kind of like with tight pants. You struggle to get them on because fabric is new. Once you wear them for even few minutes, they become easier to put on again.

Anonymous 0 Comments

It’s all folded up and cold at first. Stretching heats it up and straightens it out. When it’s warmer and smoother it will stretch easier.

Anonymous 0 Comments

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Anonymous 0 Comments

Action Lab actually did [a great video](https://www.youtube.com/watch?v=GiG0e1s6nV4) on the elastics of a balloon!

Anonymous 0 Comments

It is from two intuitive reasons ..

The big part is how tension works .. have you noticed when two droplets of water in say a glass surface meet? .. the bigger droplet always seems to ‘suck’ the smaller droplet when they merge .. thats because the bigger droplet has lower pressure inside it! .. same with balloons .. think of it this way, if you were to allow balloons/droplets to merge, if the bigger sucks in the smaller droplet, it will only slightly get bigger, so no much change in pressure/energy required, while the smaller one get to be completely flat so all the pressure there can be gone! .. this is because the energy required to hold pressure depends on surface area which grows slower than the volume inside .. hence spheres held by surface-tension (like a balloon or droplets) have lower pressure in them the bigger they get!

The second part is simply that rubber is a type of material that can be ‘preconditioned’ .. basically if you stretch a balloon several times before you try to blow into it, you’ll find its a lot easier to get it started! .. all the stretching you do before hand ‘loosens up’ the rubber (and makes it warmer etc) and if you dont do that it is stiffer and therefore harder to blow up!

Anonymous 0 Comments

Can anyone explain why my cheeks get crazy painful when I do it? I’m serious. I can’t blow up balloons my cheeks hurt something fucking serious after…

Anonymous 0 Comments

Some interesting answers. I’m sure the tension of the materials against the air has SOME effect. But largely, in my opinion, you’re overcoming the atmospheric pressure / gravity. Once you’ve inflated the balloon slightly, you’ve pressurized the system into something closer to atmospheric pressure. and the atmosphere will have a delicate balancing act with your balloon to try to meet equilibrium of pressure.

Anonymous 0 Comments

There is a certain amount of rubber in the balloon. The bigger the balloon becomes, the more the rubber is stretched, which means more force needed to inflate.

However, the bigger the balloon gets, the thinner the rubber gets, which makes the “stretching force” less!. This not only cancels out the original stretch force, but since the surface area is dependent on the square of the radius, this actually beats the linear relationship of the rubber stretching, thus making it easier to blow an inflated balloon than an uninflated one.

Anonymous 0 Comments

[There is no ELI5](https://www.sciencedirect.com/science/article/abs/pii/S0020746214001292)

Rubber has complex mechanical properties when it’s stretched, which cause the effect described by OP.

PDF of the paper whose abstract I linked to above is available on arxiv.org.