how would you measure the amount of gas in a balloon?

Question

i'm doing a sci. fair project and my teacher needs to know how i will measure the amount of gas in a balloon. i need a measurement like cm. or gallons and how i would get the measurement.

Answer 1

Assuming most balloons are pretty much round when inflated, I would measure the circumference of the balloon and convert it to the volume of the "sphere" in cubic inches. Gas can be measured in cubic inches or converted to another measurement, if needed.

Try getting one of those "pleated balloons" or punch balls as they typcially inflate as a nice sphere.

Process:
Get one of those garmet measuring strips to meaure the circumference of the balloon. Knowing that the circumfrence of a circle is 2(pi)r, you should be able to solve for the radius. You can "eyeball" the radius too by measuring the balloons apparent width and dividing by 2.

Once the radius is known, the formula for a sphere is 4/3(pi)r^3. If your units are in inches, you will get the radius in inches.

Lets run an example. Let's say after the balloon inflates you measure the circumference at 25".

Knowing that 2(pi)r = 25", you can solve for the radius.
(pi)r = 12.5"
r=12.5/(pi)
r=3.98" (or approximately 4")

The volume of a sphere is 4/3(pi)r^3, or in our example 4/3(pi)4^3...
4/3(pi)64
85 and 1/3 x 3.1415 = 268.07

It would be safe to say in this example, that the balloon has approximately 268.07 cubic inches of gas.

Now, density of the gas can also have an impact, but for the sake of your "experiment" this should work for you.

Good Luck!

Answer 2

Well if you could find a gas syringe and you could find some way of making sure that no gas escapes from the balloon into the atmosphere than that may working. Just make sure you set up the syringe perfectly horizontally or your results will be distorted.