### Meteorology: Understanding the Atmosphere            Ackerman and Knox

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Why do baseball pitchers specifically hate to pitch in Coors Field in Denver, Colorado? Believe it or not, it’s because of the frictional force—or rather, the lack of it. The result is that ordinary fly balls turn into home runs.

What forces act on a baseball in a major-league game? The pitcher throws the ball to the batter at up to 100 mph, who hits it with a wooden bat and sends the ball flying in the opposite direction just about as fast. Once the baseball leaves the bat, it is then under whatever power the batter supplied to it. (We'll ignore the wind here; sorry, Cubs fans.) Meanwhile, two forces act to ring the ball down. The gravitational force is always acting to bring it straight downward. But this force is virtually the same at every baseball stadium.

The other force acting on a fly ball is the frictional force. Here, the friction is due simply to the ball rubbing against air molecules as it sails through the air. Friction acts to slow down a baseball and keep it from carrying as far as it would in a complete vacuum.

The frictional force is not the same in all stadiums. We learned in Chapter 1 that the density of air decreases rapidly with increasing altitude. Decreasing density means fewer air molecules to rub against a soaring baseball, and a longer fly ball. Coors Field in Denver is at an altitude of about 1600 meters above sea level. This is almost one mile above sea level; in fact, the 20th row of seats in the upper deck at Coors Field is exactly one mile above sea level. Because of this, the air density there is about 15% less than at most other major-league stadiums.

How does the “thin air” in Denver affect the flight of a baseball? Use the applet below to help you determine this affect. (The applet has few simplifying assumptions such as, no wind, and the ball does not curve or slice due to spinning). To determine how far fly balls go in relation to sea level, fill out the following table. But first, set the angle at which the ball leaves the bat to 45.

 Off-the-bat velocity of the ball Distance traveled in Denver, CO Distance traveled in New York, NY Percent difference 70 90 100 110 120

About how much farther to fly balls go in Denver than at New York? Strong power hitters have an advantage: the faster the ball leaves the bat, the bigger the advantage a batter has in Coors Field versus a stadium at sea level!

You pick a city (changes the altitude), set the speed (in m.p.h., of the ball leaving the bat), set the angle (in degrees, of the ball leaving the bat), and click "Hit it".