Aurelius120
- 269
- 24
- Homework Statement
- What is the reason for placing the spirometer at 400mL mark at the start of the experiment?
- Relevant Equations
- NA
This is a water spirometer. You have to exhale as hard as possible the pulley rotates and the pointer shows the volume exhaled.
The procedure wants us to keep the pointer at 400 and later subtract 400 to get the correct volume.
Why can't we start at zero?
Teacher says it is easier to exhale when there's more air. As far as I know, the role of water is to only act as an air tight seal.
And I don't see why more air makes any difference in resistance to expansion. We have to always blow against air pressure anyways?