Air Pressure

[scistudent01]

Which case would have the highest air pressure?
a) a cold, wet day
b) a cold, dry day
c) a warm, wet day
d) a warm, dry day

[squarebear]

Perhaps you should spend more time paying attention in class? I refuse to help what is obviously someone's homework.

[scistudent01]

Thank you for your imput, but no I am not a student, I am a mom who is "trying" to help my child with summer study in math and science. All help is truly appreciated! :o)

[gen2]

Here are some facts.

When air is heated it expands and becomes less dense.

Water vapour (H2O) has a lower molecular weight than either nitrogen (N2) or oxygen (O2). Air is mostly nitrogen and oxygen so the water vapour will be less dense.

That should help you all enough to work out the answer as a scientist should - from basic facts.

[Clanad]

Here, Mom, let me help. The actual pressure of the air changes with weather pattern's as I'm sure you know. This has to do with high and low pressure systems from whence all weather related phenomena emanate. However, a given volume of air can be more "dense" than another equal volume of air, and therefore, "weigh" more. The molecules that make up air can be more closely packed together the colder they are. Additionally, the less the volume contains of other materials, such as dust or water vapor, the more closely the molecules will fit together. You can see, from this explanation, the highest "pressure" in this context, will be your example (b)... In my profession of aviation, the aircraft's take-off performance is measurably enhanced on a cold day as opposed to a warm day (shorter take-off distance). The heat has more to do with the density than does water
but both are contributory. Best of luck with the assignment!

[Clanad]

Oops, you weren't there when I started, gen2... apologies...

[squarebear]

My apologies scistudent. I saw on another thread you were helping your child.

[scistudent01]

Thankyou squarebear :o)
Ok, from info. given from gen2 and Clanad combined, (thankyou both) I am going to say the correct assumption would be cold and wet day.
Am I understanding the information correctly?

[Clanad]

No, it would be a cold and dry day...

[mibn2cweus]

Water vapour in the air is in the form of a gas and thus obey the gas laws. Water vapour, having two molecules of hydrogen to each molecule of oxygen is lighter than the nitrogen displaced by its presence making a given volume of humid air lighter than dry air.

See D. Avogadro's Hypothesis and Molar Volume, here -
https://www.chem.wisc.edu/deptfiles/genchem/sstutorial/Text9/Tx95/tx95.html