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The weight of air

28. 02. 2010.

My son came home from school (2nd grade high school) with a question for me: How much does a cubic meter of air weigh? Or, more precisely, what is the mass of a cubic meter of air, at sea level, at 20 degrees Centigrade?

He had successfully solved a physics problem in class, and as a consequence of his calculations it turned out that the mass of one cubic meter of air is, approximately, a little more than one kilogram. I was totally surprised and said that this can’t be right, but his teacher, his textbook and the ultimate authority for everything – the Internet – had apparently already confirmed this (he checked all three).

I thought he might be wrong and had to check for myself. Well, sure enough, there it was on Wikipedia in black letters on a white background – 1.204 kg/m3.

I decided to do a Twitter and Facebook poll with my dear followers / friends. I found the results really interesting.

Poll results: What is the mass of 1 m3 of air?

The answers were evenly split amongst the two extreme values – 1 gram and 1 kilogram, with 10 and 100 gram answers getting relatively few votes ( I asked in the poll question to please vote / answer without Googling first). This neck-and-neck pattern of the two opposed answers was quite consistent throughout the answering period, regardless of the number of votes.

What does this really mean? I don’t really know. I might guess that a number of voters knew this answer from before (Danica a.k.a NikiBGD was *shocked* that people would not know this .-)), getting it right, and that the ones answering “one gram” went after their intuitive guess – as I almost certainly would have done.

For me, this is just one more example of the scientific facts being really, really different from what we might expect from our own experience.

Also, it was my most-answered poll so far (it *did* take one FB posting & several tweets over a few days and thanx to all who retweeted) and also a welcome opportunity to squeeze one more blog post into the last hours of this February.

Take care y’all – comments welcome, particularly from those who noted that blog comments might be a more appropriate forum for a discussion than FB 🙂


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