# Pressure inside a balloon

• Diwakar
In summary, when filling a balloon with air at sea level, the pressure inside will equal the outside atmospheric pressure. Doubling the air mass inside the balloon will also double the pressure, but not necessarily the volume. When moving the balloon to an altitude with half the atmospheric pressure, the outside pressure will decrease, causing the balloon to deform and increase in size. However, the pressure inside the balloon will also decrease due to the equilibrium of the closed system. This means that the increase in size will be smaller than expected. The pressure inside the balloon is directly related to its volume and the force applied to it.

#### Diwakar

here is something confusing me about air pressure inside balloons. I got three questions:

Assume I am sitting at sea level, with a balloon. I fill it to 1/3 its capacity with air.
Then I place an absolute pressure sensor at its opening.
1- What pressure value do I read ?
Do I get the 1013 mbar which is the atmospheric pressure at sea level ? Because I read that the pressure inside the balloon must equal the outside pressure.

Now, I fill it to 2/3 its capacity with air.
2- What do I read now ? Is it double the pressure I got at question 1 or is it still the same ?
Remember, the outside atmospheric pressure did not change. It is still 1013 mbar. Also note the balloon has doubled its air mass.

Now, with 2/3 its capacity still filled with air, I move the balloon up to an altitude where the atmospheric pressure is half that at sea level.
3- What pressure value do I read there ?

Sort of depends on what you mean by 'capacity'. It's really a maximum volume before bursting.

The balloon's volume will contain a certain mass of air. The pressure will be a direct function of the balloon's volume at any altitude.
So, when you fill it from 1/3 to 2/3 capacity, you are doubling the mass, but not doubling the volume. Depending on how large the balloon gets, that will determine the pressure.

A balloon is an elastic. To deform an elastic, you must provide a force. If the force inside is greater than the one outside, the area extends. Since we're talking about force and area, we can also talk about pressure. If a balloon has deformed, then the pressure inside has to be greater than the one outside. The greater the deformation, the greater the pressure differential (Pin - Pout). This takes care of your points 1 & 2.

For point 3, what happens is that you are reducing the outside pressure which has the same effect as increasing the inside pressure, i.e. increasing the deformation of the balloon. The interesting thing is that the inside of the balloon is a closed system so, as the balloon increases in volume, the inside pressure will also decrease. The equilibrium will be reached faster, so the increase in size will be smaller than one could have initially thought.

## 1. How does the pressure inside a balloon change when it is inflated?

The pressure inside a balloon increases as it is inflated. When air is blown into the balloon, the molecules of air become more crowded and collide with the walls of the balloon more frequently, resulting in an increase in pressure.

## 2. What happens to the pressure inside a balloon when it is heated?

The pressure inside a balloon increases when it is heated. This is because the molecules of air inside the balloon gain kinetic energy and move faster, causing them to collide with the walls of the balloon more forcefully and increasing the pressure inside.

## 3. Why does a balloon burst when it is filled with too much air?

A balloon will burst when it is filled with too much air because the pressure inside becomes too great for the elastic walls of the balloon to contain. The balloon will burst at its weakest point, usually near the knot or opening.

## 4. Does the type of gas inside a balloon affect the pressure?

Yes, the type of gas inside a balloon can affect the pressure. Different gases have different molecular weights and behaviors, which can impact the pressure inside the balloon. For example, helium gas is less dense than air and will result in a higher pressure inside the balloon.

## 5. What happens to the pressure inside a balloon when it is squeezed or compressed?

The pressure inside a balloon increases when it is squeezed or compressed. This is because the molecules of air are being pushed closer together, resulting in more frequent collisions with the walls of the balloon and an increase in pressure.