The
bowling ball is simply the
sphere rolled by the
bowler down the
lane to hit the
pins. The details of the ball beyond that point are determined by the specific type of bowling being done, as the
sizes and
weights and methods of use vary
radically.
The bowling ball started out simply as a spherical stone back in the early days, when Kegels were used instead of pins. Eventually a wooden ball came to be in use, as it was easier to get the proper shape, and lighter. The wood eventually came to be lignum vitae, very hard and strong.
In 1905, the first ball using rubber, the "Evertrue", was introduced. 1914 saw Brunswick promoting the "Mineralite" ball, with it's "mysterious rubber compound", and soon wood was left behind.
Canadian 5-pin bowling, duckpin bowling, and candlepin bowling use a ball that is around the size of a softball. It weighs approximately 3.5 pounds, and while there's a large variety of materials and colors, the size and weight will be consistent.
Tenpin bowling balls may vary between 6 and 16 points. They can be made from a variety of materials. The ball may have up to five holes for gripping, though three is the most common. (there are also commonly a small hole for balance, but it is counted seperately) Most of the details in the rest of the writeup be specific for this type of ball.
A bowling ball usually has an outer shell made of a material such as plastic, polyester, or urethane, and an inner core which is a composite of various materials. Rubber used to be common, but as the coatings of bowling lanes, and the oils used on them, changed, other materials became more suited.
A bowling ball has holes drilled in it for the player to grip and throw the ball. To keep the ball from going out of balance because of the weight removed, the core of the ball has something known as a "block". Made of denser material, the block not only compensates for the drilling, to keep the ball in balance, but is often done in varions shapes, and sometimes in multiple pieces, to affect the rotation of the ball. Because the block is asymmetric, a bowling ball can only be drilled in certain locations to leave the ball usable - and the different locations cause the ball to rotate differently. Many pro shops now even use a computer to determine the exact location for drilling for optimum balance and performance.
However, the balance for a bowling ball does have certain specifications that need to be met, to prevent an advantage from being gained from a misweighted ball. For a bowling ball over ten pounds in weight, there can only be a three ounce difference between top and bottom, one ounce between the sides, and one ounce between the finger and thumb locations. (The "top" of the ball is defined by setting the ball so that the finger holes point straight up) The various locations are measured differently because a bowling ball thrown in the proper way does not simply roll end-over-end on the lane, but rotates at a slight angle - meaning the ball is sliding down a significant portion of the lane. Looking at a ball after a shot will show the trail of oil on the ball.
A bowling ball will never have any metal or metallic substance included in it. Also, the surface of the ball must register at least a hardness of 72 on a durometer. This is done because a softer surface will have more traction on a lane, and will react differently than a harder surface. Similarly, there are restrictions on how smooth or rough the surface of a bowling ball may be.
A bowling ball may be drilled for two main grips. The grip used in a house ball, and by beginners, is known as the conventional grip. The fingers are inserted up to about the second knuckle. This allows the bowler to hold the ball more easily, but severly limits how the ball can be delivered (rolled).
The second method, used by more experienced bowlers, is called the fingertip grip. The hole is drilled only deep enough for the fingers to be inserted to about the first knuckle. Often, rubber inserts called "fingertips" will be placed in the holes to make it easier to hold the ball - it can be difficult to hold a 16 pound ball with that little of your fingers against a smooth surface. The ball tends to be delivered with the hand coming around the side with this method, causing more spin on the ball.
Bowling balls today tend to run $150-$250 for a good ball, though a casual bowler looking simply for their own ball can usually find a good one for $60, though there are often cheap plastic models that go for as little as $30.
Most serious bowlers have more than one bowling ball they use. This is because, as stated above, they have differences in weight, balance, and surface. Bowling lanes are not consistent in how much oil they have on them, or where the oil is located, even during a series, as the repeated bowling on them will cause the oil to shift around as it is picked up by the ball and redeposited elsewhere on the lane. A variety of bowling balls allows a bowler to find one that handles the conditions the best, allowing them to use their regular form.
Some bowlers will even use a different ball for their first frame and their second frame - using one that will hook less for their spare shot, as the accuracy is more important here, and one with a greater hook for the strike shot, so the ball will "drive" into the pocket better than a straight shot.