These come in many forms. The best golf ball for the low handicap player is a balata ball. This has a balata coating on the cover which adheres to the club face longer than a "hard ball" (usually surlyn) thus creating more spin and a better ability to stop the ball where it lands.

High handicap players usually want more distance, so they tend to use harder balls.

Golf balls sell for as little as $15 a dozen up to $50 a dozen. You get what you pay for.

A conventional typewriter has a lever connected to each key; striking the key forces the lever against the ink ribbon, where the letter imprinted at the tip of the lever makes its shape appear on the paper. Clearly, replacing the font or character set is a major undertaking -- all levers must be retooled.

The golf ball is ellipsoidally shaped, and has all the letter imprints on it. This makes it look a (little bit) like a golf ball. When you hit a key, the typewriter rotates the golf ball (along 2 axes!) so the correct imprint is facing the paper, then strikes the entire ball against the ribbon and paper. Replacing the font or character set is trivial -- just pop off the old golf ball and pop in a new one.

updated 18-Jul-1997 by PEG
updated 17-NOV-1993 by CDF
original by Craig DeForest

Why are Golf Balls Dimpled?

The dimples, paradoxically, do increase drag slightly. But they also increase `Magnus lift', that peculiar lifting force experienced by rotating bodies travelling through a medium. Magnus lift is present because a driven golf ball has backspin. The same Magnus effect can cause a ball to hook or slice if there is sideways spin.

Contrary to Freshman physics, golf balls do not travel in inverted parabolas. They follow an 'impetus trajectory':

                                    *    *       
                              *             *
(golfer)                *                    *
                  *                          * -- trajectory
 \O/        *                                *
  |   *                                      *
-/ \-T---------------------------------------------------------------ground

This is because of the combination of drag (which reduces horizontal speed late in the trajectory) and Magnus lift, which supports the ball during the initial part of the trajectory, making it relatively straight. The trajectory can even curve upwards at first, depending on conditions! Here is a cheesy diagram of a golf ball in flight, with some relevant vectors:

                             F(magnus)
                             ^
                             |
                F(drag) <--- O -------> V 
                          \     
                           \----> (sense of rotation)

A golf ball leaves the tee with a speed of about 70 m/s and a backspin of at least 50 rev/s. The Magnus force can be thought of as due to the relative drag on the air on the top and bottom portions of the golf ball: the top portion is moving slower relative to the air around it, so there is less drag on the air that goes over the ball. The boundary layer is relatively thin, and air in the not-too-near region moves rapidly relative to the ball. The bottom portion moves fast relative to the air around it; there is more drag on the air passing by the bottom, and the boundary (turbulent) layer is relatively thick; air in the not-too-near region moves more slowly relative to the ball. The Bernoulli force produces lift. (Alternatively, one could say that `the flow lines past the ball are displaced down, so the ball is pushed up.')

The difficulty comes near the transition region between laminar flow and turbulent flow. At low speeds, the flow around the ball is laminar. As speed is increased, the bottom part tends to go turbulent first. But turbulent flow can follow a surface much more easily than laminar flow.

As a result, the (laminar) flow lines around the top break away from the surface sooner than otherwise, and there is a net displacement up of the flow lines. The magnus lift goes negative.

The dimples aid the rapid formation of a turbulent boundary layer around the golf ball in flight, giving more lift. Without 'em, the ball would travel in more of a parabolic trajectory, hitting the ground sooner (and not coming straight down). This was discovered by accident in the early days of golf when golfers noticed that old roughened golf balls went further.

Despite the drag, a dimpled golf ball can even go further in air than it would in vacuum given the same initial velocity and low angle. However, a golf ball shot at 45 degrees and 70 m/s in vacuum would go 500 metres to the first bounce, which exceeds all records.

References:

Lord Rayleigh, "On the Irregular Flight of a Tennis Ball", _ Scientific Papers I_, p. 344

Briggs Lyman J., "Effect of Spin and Speed on the Lateral Deflection of a Baseball; and the Magnus Effect for Smooth Spheres", Am. J. Phys. _27_, 589 (1959). Briggs was trying to explain the mechanism behind the `curve ball' in baseball, using specialized apparatus in a wind tunnel at the NBS. He stumbled on the reverse effect by accident, because his model `baseball' had no stitches on it. The stitches on a baseball create turbulence in flight in much the same way that the dimples on a golf ball do.

R. Watts and R. Ferver, "The Lateral Force on a Spinning Sphere Aerodynamics of a Curveball", Am. J. Phys. _55_, 40 (1986)

Steve Haake, "Physics and Golf? You must be joking!" Physics World _10_, 76 (1997)

Journal of Applied Physics 20, 821 (1949) by Davies.

American Journal of Physics 56, 933 (1988) by McPhee and Andrews.

"The Physics of Golf" by Theodore P. Jorgensen

In the beginning of golf history, early 15th century, golf balls were made of wood. Soon the players realized that this didn't exactly give them the control they wanted, so they started sewing leather pouches that were stuffed with feathers. The pouches were sewn while wet and the feathers were wet as well. When dried, the feathers expanded and the leather shrank. Pretty clever if you ask me... This was in the late 15th century.  

Anyhow, in 1840s the gutta-percha gum was discovered. It came from the Malaysian Palaquium tree and it was heated and molded into a small ball. It was very inexpensive and much more durable than the feather balls. The guttie was a huge success and made the game a little less exclusive. Soon players started to notice that old and worn balls flew longer and straighter than new, smooth, ones. They realized that the marks and scratches made the ball go longer. The makers of the gutties adapted and started manufacturing the balls with different patterns and marks on the balls. Being a purely experimental practice, the results varied. Today we have well developed theories of aerodynamics and know how this works. See Why are Golf Balls Dimpled?

In 1898 the first rubber golf ball was produced. It had rubber thread wound around a rubber core. After a while the makers started putting shells on top of the rubber thread to make it more durable. They choose balata, a latex from the tropical bully tree. It was strong and lasting. In 1908 William Taylor started putting dimples on the balata surface of the ball, which increased the length of the ball flight. 

It took until 1930 for the golf ball to become standardized to weighing 1.62 ounces (45.93 grams) and having a minimum diameter of 1.68 inches (4.27 centimetres). Today initial velocity, driver distance and symmetry are also being regulated. 

Until recently, the balata ball from the early 20th century has been the one in use. However in the late 1990s a new type of solid core balls, with a thin polymer layer inside a urethane shell were becoming more and more advanced. Today most professionals use this new type of synthetic sold core balls, which provide greater ball control and distance. The latest model from Titelist, Titleist Pro V1 have been at the top of the leaderboard constantly since its introduction in October 2000.

The golf ball market is worth over $ 1 billion per year, and the big names are Titleist with some 45% market share, Spalding (Top-Flight and Strata) with a little over 20% and then follows Maxfli, Precept, Wilson, Nike, TaylorMade and Callaway.

Source: britannica, scientific american

Weight
The maximum weight of a golf ball is 45.93g. A heavier golf ball would travel farther.

Size
If it's smaller in diameter than 42.67mm, it's too small to be legal. To find out if it is, it is dropped through a hole of 42.67 mm and deemed acceptable if it does not fall through the hole more than 24 times out of 100. (No, I am not making this up.)

Symmetry
Yes, a golf ball must be round - and behave like a round object, which means that hidden, off-center weights are a no-no.

Initial speed and maximum length
Using a test apperatus, the ball is whacked by a clubhead and must not fly farther and faster than the standards allow.