Buoyancy

I used to read to my kids from a popular children's book which featured a curious monkey who got into trouble by grabbing a large bunch of helium balloons from a balloon salesman.  According to the storyline, the monkey was carried out over the city hanging from the balloons.  Now, I'm sure the illustrator for the book was deeply interested in thermodynamics (isn't everyone?) but may have been in too much hurry to calculate the appropriate number of balloons.  Or maybe artistic aesthetics overruled thermodynamic accuracy.  In any case, today we'll go back and look at the situation in more depth.

Altitude vs Temperature

People who ski, hike, run, or do other vigorous exercise at a higher altitude than usual typically feel some effect of the elevation.  It is common to feel difficulty getting enough breath.  Conversely, sometimes people who travel down from a higher altitude feel like they can run faster and longer than usual.  The cause, of course is that the lower density air at higher altitude provides less oxygen.  At a given altitude, though, the density of air also varies with the temperature.  In this post, we’ll look at the size of that effect.