Re: How do temp, press, humidity affect the distance traveled by golf balls?

There are a handful of answers on the MadSci Network that deal with the effects of wind, humidity, and pressure with baseballs and airplanes, but not too much on golfballs. Here are 3 such responses I found with the search engine.

Re: Does the temperature of a baseball affect it's rebounding rating?

Re: differences in gravity at sea level & 1 and 2 miles alt.?

Re: How do acrobatic planes fly?

However, the simple answer is that it is not simple. So, like most physics questions, we can either do the experiment when appropriate, or try to compile the basic principles we understand and create a model. We have to accept the fact, that we don't know it all (physicists say this all the time), and try to hit the most important features. And sometimes, even after considering the apparently most important effects, we are still wrong because we missed something. Permit me a huge digression to evaluate temperature, humid, and air pressure and then come back to the question.

Modelling the flight of a golf ball is very difficult to do accurately. Golf ball manufactures do many things almost completely by trial and error when it comes to designing new golf balls. Experience and creativity are what lead to the which new dimple patterns, ball materials, and core construction is attempted. Because of the variability of balls, and the huge computational burden it would take to try to account for the dimples, drag, speed, density of the air, wind, and such, we must turn to what simple things we know.

There are a few generalities that can be applied.

First let's look at temperature. Anyone who has played golf,baseball or tennis when the temperature is below about 45 ^oF can tell that the contact with the ball feels different than at more spring/summer-like temperatures (60+ ^oF). Part of the reason is that the ball is less resilient (this goes for the club too). When the ball is struck more energy is lost, so the ball doesn't travel as far. Throw in harder ground and when the golfer swings to hit the ball, the ground can (not always) create more drag or less solid contact with the club face. The ball might roll farther on the ground, but it is likely that the competing effects will win.

Humidity is often underrated. Humid air is lighter than dry, despite what people say about the air being heavy. The heaviness of humid air is more from the reduced ability to cool down by sweating and the slight rise in breathing difficulty. Gaseous water (H₂O) is lighter then the N₂ or O₂ that is replaces. I have experienced the effects of humidity while playing golf and softball. I used to live in St. Louis which a terribly humid place during the summer and fall. I played in a softball league that played games during the summer with start times that ranged from 6:00PM to 10:30PM. The later games typcially were played in a slight fog that arose because the field was in a valley. During the fog games, everyone could be a power hitter. I could routinely hit a softball over 300 feet at 11:00PM, but was lucky to clear 250 feet during the sunny games of 6:00 PM. If you look at Major League Baseball many of the dome stadiums used to be very poor for home runs (the Astrodome in particular), I think in part to the lower humidity that was prevalent for customer comfort.

The extreme of rain on the other hand will shorten the flight of a ball. The main reason is the constant pounding of the water against the ball. The rain drops work like little hammers of momentum to slow the ball down.

Finally let's consider air pressure which has probably the biggest effect of the three. Simple stated, less air pressure means less aerodynamic drag (air resistance). Viscosity (drag through a fluid) is inversely proportional to air pressure (or density, really). Since the golf ball does not depend on air pressure (or density) for thrust (like a jet engine), it will fly farther. The effects of air pressure (density) are usually approximated as linear. This is not a great approximation all the time, but it pretty close. Therefore, a 10% drop in air pressure will turn a 240 yard drive into about 267 yards.

If we look at the records of well known long driver Gerry James, we can see the effects of elevation (i.e. low air pressure) on distance. Notice the big hits all occur in Colorado, Nevada, and Arizona.

Winner: Pro longest drive event,
        Houston Texas, 396 yards,
        June 1993

Winner: Pro longest drive,
        Cooper Creek, Colorado, 417 yards 1/2 inch @altitude,
recorded/filmed.
        1991

Pro Longdrive Championships:
        Miami, Florida, 410 yards,
        November 1991

World Record Breaker Pro Longdrive Event:
        448 yards, 2'3" Denver, Colorado, @altitude,
        October, 1991

Winner: Metter,
        Georgia, 381 yards,
        October 1992

Winner: Pro longdrive event, BLASTERS,
        Baton Rouge, Louisiana, 319 yards (into 25 mph winds)

Winner: Pro longdrive, DUNAWAY'S RUNWAY, Championship,
        362 yards, filmed,
        June 1995

Winner: NITRO SHOOTOUT,
        Mesquite, Nevada, 419 yards, filmed,
        April 1997

Winner: Casa Grande, Arizona.
        longdrive 444 yards,
        July 1997
Winner: Hard Drive Power Golf Tour,
        Denver, Colorado, 473 yards 2 feet 6 inches (competitive world
record)
        September 28, 1997.

Gerry James is not a huge guy, but he knows how swing the driver. The folks that hold the long drive contests also know enough to stage their events in the mountains.

So with all this background, let's go back to your question:

If water vapor is lighter than dry air, why do balls seem to travel less
distance in high humidity conditions?

-Hot, humid day with less wind, the golfer will get tired.
-Wet and humid days the ground will be soft and this will reduce roll and potentially allow the golfer to dig more turf at contact.
-We don't understand something fundamentally different about how the ball interacts with the air when it is more humid.
-This is a placebo effect: the ball is probably travelling about the same distance and we have created an observation. A similar myth was that batters popped out more with aluminum bats. This was widely accepted back in the mid-70's and early 80's. This is simply not true.

In general, your average golfer does more poorly when the course conditions are not "average." So any variation from 75 degrees and partly sunny with a light breeze creates the conditions for observations of phantom effects. I, for example, often play horribly when the course is very wet because I tend to be in the heavy wet rough and if I miss swing slightly I get a big old hunk of sod in the fairway.

Sincerely,

Tom "No Short Game" Cull