Baseball Physics: Warm and Humid or Cool and Dry?

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By Stephen Barabas on March 19, 2012, 11:05am

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Ever play baseball during the cold weather months?  I recall practicing early in the morning when it was in the 30s or 40s, and the sting the bat would leave on my hand after hitting the ball.   It sucked!  It also seemed like the ball just wouldn't travel as far as it would on warmer days.

Over the years I learned that in fact, warm air is less dense than cold air!  When the air warms up outside, air molecules are spread further apart, resulting in air that is less dense.  Thus, when you hit or throw a ball, there's less frictional drag acting upon the sphere.  The ball will travel faster and farther.

On another note, we're all familiar that when it warms up, we tend to get pretty humid on some days.  Now, a lot of people might not know this, but moist air is actually less dense and lighter than dry air!  How can this be?  Well the fact lies within chemistry, where the air is made up of about 78% nitrogen atoms and 21% oxygen atoms.  These atoms are weighted heavier than actual water vapor molecules.

Italian physicist Amedeo Avogadro discovered in the early 1800s that a fixed volume of gas at the same temperature and pressure would always have the same number of molecules no matter what gas is in the container.  As moisture advects in, water molecules replace nitrogen and oxygen, and have a molecular weight of 18g/mol.  These are in fact lighter than both nitrogen and oxygen.  So, by replacing nitrogen and oxygen with water vapor. causes in a decrease of the weight of the air. . .  it's density decreases.

If you're aiming to hit that home run, or practice the Magnus effect with your curveball . . . practice on warm, humid days.

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Stephen Barabas

Town: Southbury, CT  

Reporting for WXedge since January 2012.

Articles: 56

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