Why is it necessary to change the balloon diameter to liters when find lung capacity?

Answer 1

Lung capacity is a volume; you need the volume of the balloon which is measured in cubic centimetres (cm³).

If the balloon is a sphere with a diameter d which can be measured, then its volume can be calculated as:

volume = 1/6 × π × diameter³

Answer 2

You can find many copies of this experiment on Google in DOC, DOCX, and PDF formats. Here is one such site: classroom.misd.org/users/0211/Lung%20Capacity%20Lab.pdf(The classroom website will open a download box so you can save the file to your hard drive.)

This experiment uses a metric ruler to measure the expanded balloon, in centimeters (cm). However, lungs hold a volume of air. Lungs are not flat or one dimensional. So you use a graph to convert the measurement to liters.

Another way to think of this is to take a ZipLock Baggie and lay it on a table. Use the metric ruler to measure the flat baggie at its widest point. Write that number in cm. Now, put 1/2 of a peanut butter sandwich into the baggie and close it but leave the air inside the baggie. Lay it on the table again. You can see how the baggie has depth; it is no longer one dimensional. It is the same when you use your lungs to push air into a balloon in the longest breath you can muster. You need to change it the measurement to liters to show the amount of air you put into your balloon.