Trees and Sports: Equipment Made from Wood (Basic)

Baseball

On a recent outing to Seattle, a friend and I strolled past Safeco Field, home of the Mariners, our city’s major league baseball team. The outside walls of the ballpark were hung with giant portraits of the players: Justin Smoak, Franklin Gutierrez, Ichiro Suzuki – heroic, larger than life, powerful. I thought about all the children who looked up to these athletes and wanted to be like them. I also wondered how trees might play some part in that exchange. My friend informed me that professional players use only bats made of wood. According to the major league rules, a bat must be no more than 2-3/4 inches in diameter and no more than 42 inches long, and consist of a single, round piece of solid wood. There was my connection between this sport and trees.

When baseball was invented in the 1850s, bats came in all shapes and sizes and were made of hickory, an extremely hard and heavy wood. Today, the majority of wood baseball bats are made from deciduous trees harvested from Pennsylvania and New York. White ash (Fraxinus Americana) and sugar maple (Acer saccharum) are used because of their hardness, durability, strength, and ‘feel’. Trees that provide the lumber for baseball bats are around 50 years old. Metal bats, introduced in the 1970s as a cost-saving alternative to wooden bats that were prone to breaking, turned out to be more efficient than wood. In a study by J. Crisco and R. Greenwald at Brown University, metal bats outperformed wood bats in test comparisons. They clocked average ball speeds for wooden bats at 98.6 mph, and for metal bats at 103.3 mph. Claims that higher ball speeds put infielders at greater risk for injury have led to calls for restrictions on bat performance. Some athletic associations have banned the use of metal bats in high school play because bats made of wood seem safer. Learn the basics of wood vs. aluminum bats here.

Indoor Sports

The wooden floor underneath the action of indoor sports such as basketball gets far less attention than the athleticism displayed on court, yet it is a critical part of the safety and performance of the athletes. A sports floor must be durable, resilient to the pounding of heavy players, provide just the right amount of friction to prevent falls, and allow for slides and quick turns. As an athlete’s foot hits a sports surface, the force is translated into two forces, one absorbed by the floor, the other returned to the athlete. Artificial surfaces such as concrete and asphalt provide little force reduction for the athlete but maple sports floors absorb these forces, which reduces injury to the athlete. One study documented that athletes were 70 percent more likely to sustain a floor-related injury on a synthetic floor than on a wooden floor. Starting 150 years ago, Northern Hard Maple (Acer saccharum) became the sports floor of choice because of its resilience and traction. In the United States, each year, 17 million square feet of sports floors are annually installed, equivalent to about 85,000 trees that are 70 feet tall and 14 inches in diameter.

Golf


white-golf-ballThe materials that make up golf balls have evolved through the long and fascinating history of golf. Historically, these materials were linked to natural compounds, all of which were derived from objects in nature, particularly different species of trees.

The Scots, who originated the game in the 1400s, developed a variety of golf clubs: irons, putters, and woods. Woods are the longest clubs in the bag and are mostly used for long shots. The wood heads were made of persimmon (Diospyros) or maple (Acer) trees. The introduction of golf into America in the early 1800s led to the use of hickory (Carya) (native to the United States, but not to the United Kingdom) in the shafts of the clubs. These clubs were far stronger than other woods and became standard until steel shafts were introduced in 1925.

The first balls – called “featheries” – were leather-covered objects stuffed with boiled goose or chicken feathers., and then coated with paint. Feathers were first boiled and then placed in the pouch. As the ball cooled, the feathers would expand and the hide would shrink, making the hard, compact ball that would fly far and accurately.

Later, tree products entered into the golf ball. The “gutta-percha” ball was created in 1848. Gutta-percha is the evaporated milky latex from Malaysian Sapodillo tree of eastern Asia, Palaquium gutta. This and other related trees, such as the “bully tree” (Manilkara bidentata) of the West Indies, yield a hard rubber-like material called “balata.” Trees are tapped by cutting zigzag gashes in the bark, something like the harvest of maple sap to make maple syrup. The latex was collected in cups that hung from the trunk. That raw material turns into a tough, resilient, and water-resistant material.

The rubber was made round by heating and shaping it while hot. However, since the ball was spherical, it creating little lift and went only short distances. Accidentally, it was discovered that defects in the sphere from knicks and scrapes of normal use could provide a ball with a truer flight than a pure sphere. Thus, makers started creating intentional defects in the surface by hammering the ball to give it an evenly “dimpled” surface, which caused the ball to have a more consistent ball flight.

By: Nalini Nadkarni, University of Utah

 

References:

Nadkarni, N. M. 2008. Between Earth and Sky: Our Intimate Connections with Trees. University of California Press. Berkeley, CA, USA.

Tennis Courts and Equipment: How Physics Affects the Speed of Play

tennis ballsTennis is played internationally.  Depending on what nation hosts a tennis tournament, players may find themselves competing on anything from grass (Wimbledon) to clay (Australia) to rubber coated concrete with acrylic paint (U.S.).  Other variables within the sport include ball types and rackets.

Different court surfaces, balls, and rackets impact the speed of the game. One way to address the issue of speed is to combine a faster court with a slower ball, or a slower court with a faster ball, to level out the pace.  Additionally, scientists continue to study the composition of rackets, shoes, balls, and court material to find solutions to these and other ongoing issues in the sport.

Learn the basics of how physics affects the speed of play or read the more technical explanation.

Articles by Lindsay Sanford

Tennis Courts and Equipment: How Physics Affects the Speed of Play (Basic)

UTAH MEN'S TENNIS Ben TasevacModern day tennis is a game of power, speed and spin.  Improvements in tennis rackets allow players to hit the ball harder and faster than ever before.  This faster pace has made the tennis serve more dominant in tennis matches, which means that tennis points can happen quickly.  There is some interest in slowing down the game to make points last longer. One approach is to engineer tennis balls differently, so that the balls themselves can be selected to adjust the speed of play. Another approach is to consider the properties of the court surface.

There are three main types of court surfaces used in tennis: grass, clay, and acrylic.  Each court is considered to have its own “speed.” Grass courts are firm and have a slippery surface.  When the ball hits the surface, it tends to slide and will have a low bounce.  This means that the player has little time to react and move, making grass a “fast” paced surface.  Clay courts, made of small pieces of crushed rock, are considered to be a “slow” surface. This is because the rough surface prevents the ball from sliding when it hits the court. This causes the ball to bounce much higher, giving the player more time to move and to choose how and where to hit the ball.  Acrylic courts are “medium” paced surfaces.  They have an asphalt or concrete base with a playing surface that is made of acrylic paint mixed with sand.  These courts are the most commonly used and require the least amount of maintenance when compared to either grass or clay surfaces (Lees 2003).

Three types of balls have been developed for use on the different types of court surfaces.  The balls vary in size and firmness. The standard ball is the type 2 ball.  It is intended for use on medium paced surfaces.  The type 1 ball is the same size as the type 2 ball, but it is firmer.  This means that it will not change shape as much when it hits the court, so it is a “fast” ball.  Type 1 balls are designed for use on “slower” surfaces such as clay.  Type 3 balls are larger than type 2 balls.  This means that they have a harder time moving through the air, so they will travel slower.  “Slow” type 3 balls are designed for use on “fast” surfaces such as grass.  With a variety of tennis balls to choose from, players can adjust the speed of play to complement court conditions.

Learn the technical details of how physics affects the speed of play.

By: Lindsay Sanford, University of Utah
Lindsay received her B.S. in Mechanical Engineering from Washington State University and is currently pursuing a PhD degree in Bioengineering. In her spare time, she likes to travel, hike, read, and play with her two year old son.  She is also an avid runner and tennis player.

 

References

Lees, A. 2003. Science and the major rackets sports: a review. Journal of Sports Sciences. 21(9): 707-32.

Tennis Courts and Equipment: How Physics Affects the Speed of Play (Technical)

Introduction

Technological advancements have played a key role in making power and spin prominent features in the game of tennis.  The transition from wood to composite graphite rackets has produced larger sized rackets (in terms of both head and shafts) with frames that are thicker and lighter (Brody 1997), allowing players to hit harder than ever before. Changes in racket construction have altered the tennis serve, to the point where serves can dominate many tennis matches.  In order to make match points last longer, scientists and athletes have explored ways to slow the serve and restore balance to the game. One approach has been to engineer new types of tennis balls with properties that can counteract the power and speed of the serve (Haake et al. 2000).  Changes in tennis ball construction and interactions between the ball and different types of court surfaces have become primary considerations.

Types of Tennis Court Surfaces

Tennis was first played on natural grass courts.  Modern day grass courts consist of a soil foundation with a seeded turf overlay (Miller 2006).  While grass is still used at Wimbledon, its use has diminished due to the cost associated with high maintenance.

Clay courts gained favorability in the 1950s and consist of a base layer of crushed stone covered with a layer of rough particle material such as crushed brick (Miller 2006). This produces high amounts of friction between the ball and surface, but low amounts of friction between the player and the surface. On a clay court, the player has a tendency to slide, particularly when slowing down or attempting to change their direction of movement (Miller 2006).  Lower injury rates have been associated with players that frequently use clay courts (Dragoo et al. 2010), possibly because of lower impact forces due to the sliding motion.  Currently, the French Open is the only major tennis tournament played on clay.

Acrylic hard courts have rapidly gained popularity since their introduction in the 1940s and are used in two major tennis tournaments, the US Open and the Australian Open.  These courts utilize either asphalt or concrete as the foundation layer, a rubber mid-layer, and a top coating made of an acrylic paint/sand mixture (Miller 2006).  These courts produce the highest amount of friction between the surface and player, and have been associated with the most player injuries when compared to other surfaces (Dragoo et al. 2010).

Tennis Court Surfaces Affect the Speed of the Game

One of the most important considerations in tennis is the influence of the court surface on the ball.  Aside from the force of gravity, a bouncing ball additionally experiences normal and frictional forces (Brody 2003).  The normal force acts perpendicularly to the surface and the frictional (or sliding) force will act parallel to the surface (horizontally). The combination of these forces impacts the bouncing movement of the ball. The amount of friction generated between the ball and court dictates if the court is considered to be “fast” or “slow.”  In particular, the amount of sliding friction that is present, dependent upon the surface type, is of interest.

A “slower” court is one where more friction is generated between the ball and the surface.  Clay, with its rough surface composition, has a high coefficient of friction.  When more frictional contact is produced, the horizontal speed of the ball is reduced.  This reduction in forward motion creates a high vertical bounce. The longer the ball is in the air, the more time a player has to move and react, making clay a “slow” paced court.

A “faster” court produces less friction between the ball and the surface.  Grass, with its firm and slippery (even more so when wet) surface composition has a low coefficient of friction making it a “fast” paced surface.  With less friction, the ball will slide more easily across the surface, and it will retain more of its horizontal speed. This produces a low vertical bounce.  For these reasons, points on “fast” surfaces are often much shorter, as a lower bounce means the player has less time to react and move towards the ball.  In an examination of rally lengths in men’s singles tennis, 66%  of rallies on clay lasted less than six seconds, but this figure increased to 88% on grass courts (Lees 2003).

Engineering of Tennis Balls

In order to engineer tennis balls with more desirable properties, understanding ball construction is important. The two main components of a tennis ball are the core and covering.  The core is typically made of natural rubber that is mixed with powder fillers to produce desirable properties, such as strength and color (Manufacture).  The outer surface is made of cloth material; either of a wool-based fabric (Melton) or less expensive cloth (Needle cloth) that contains more synthetic components (Manufacture).  In addition, most tennis balls are pressurized, and the amount of internal pressure (ranging from 0-15 psi) will be determined based upon the ball type (Miller 2006).

Tennis balls are manufactured through a series of processes. The first of these processes is an extrusion, where the rubber is forced into a cylindrical shape through an application of pressure (Manufacture). The resultant rubber rod is then sectioned into smaller segments.  Subsequent processes include forming the material into a spherical shape (by using a hydraulic press to form two individual hemispheres that are later joined), curing and pressurizing the ball, covering the ball with fabric and finally joining the core and covering together in a molding process that utilizes pressure and heat (Manufacture). The final step is to steam the ball, thus producing a more raised outer covering.  Once finished, balls must pass tests related to mass, size, compression and bounce (ITF 2012).

There are three major categories (types 1-3) of tennis balls, each designed for specific use on set court types to speed up or slow down play.  The weight and rebound of the tennis balls does not change across type.  The standard and most utilized ball type is type 2, as it is suitable for medium paced surfaces.  Type 1 balls are the same size as type 2 balls, but are harder, which is reflected by smaller amounts of forward and reverse deformation, when compared to the type 2 balls (Miller 2006).  Because type 1 balls are considered to be “fast” balls, they are suggested for use on slower surfaces such as clay.

Type 3 balls differ from type 2 balls only in size.  Type 3 balls are typically 6-8 percent larger than type 2 balls (Miller 2006).  As demonstrated by Andrew et al. (2003), Type 3 balls are “slow” and travel through the air more slowly than their standard tennis call counterparts. Since type 3 balls are larger in size, they encounter greater drag (resistance) when traveling through the air. Thus, type 3 balls are suggested for use on faster court surfaces, such as grass, to help slow down the pace of play and reduce the dominance of the serve.  Furthermore, the additional drag associated with type 3 balls also allows for a larger amount of spin to be generated (Blackwell 2007).  Type 3 balls may also be beneficial for new players, as a slower pace allows for more reaction time and increased spin can aid in accuracy.

Although less prevalent, there are also balls designed for use at high altitude.  By changing either the internal pressure of the ball or the elasticity of the core material, high altitude balls can be made to bounce lower than type 2 balls  (Miller 2006).  This is done so that at the lower air density at higher altitude the same bounce height (as that of a type 2 ball at sea level) can be achieved.

Other Tennis Ball Considerations

Despite careful efforts to engineer tennis balls and select a ball that complements court conditions, there are additional factors that impact the speed of the game. One of these is unavoidable ball wear-and-tear, which affects even the most well-engineered tennis balls.

Four distinct phases of tennis ball wear have been identified: new ball, loose fuzz, tufted fuzz, and finally the bald ball (Steele et al. 2006).  The ball covering itself is porous, which creates additional instances of drag (Mheta et al. 2001) when compared to a smooth covering.  As the surface material becomes worn, the “fuzz” on the ball is depleted, and both lift and drag forces are reduced (Goodwill et al. 2004).  The drag coefficient for new tennis balls was found on average to be higher than 0.6. The drag coefficient was reduced to values near 0.5 for worn balls (Mehta et al. 2001). This means that a worn ball will fly faster with less force to push it down when compared to a newer ball, increasing the likelihood that the ball will be hit out of play.

The impacts of a worn ball may be reduced if a player applies spin to the ball. Spin is possible due to the Magnus effect, or a nonsymmetrical distribution of air that flows across the ball surface while it is in flight (Mehta 1985, Miller 2006).  When topspin is applied, some of the air (that is flowing in the same direction as the spin of the ball) will interact with the ball surface longer, which has the effect of deflecting the wake of the ball upwards while other forces act in a downwards direction (Mheta et al. 2001, Miller, 2006). By applying topspin to the ball, a player can help a tennis ball fall to the ground and remain in-bounds.

What Players Should Know

Beginning players may be most successful on clay courts, since the speed of play is likely to be slower, and the player is better able to slide

  • A type 2 ball is most common, but a beginner may consider using a type 3 because of its slower air speeds
  • Old, worn balls do have a noticeable impact on play

 

By: Lindsay Sanford, University of Utah
Lindsay received her B.S. in Mechanical Engineering from Washington State University and is currently pursuing a PhD degree in Bioengineering. In her spare time, she likes to travel, hike, read, and play with her two year old son.  She is also an avid runner and tennis player.

 

References

Andrew, D., J. Chow, D. Knudson, and M. Tillman. 2003. Effect of ball size on player reaction and racket acceleration during the tennis volley. Journal of Science and Medicine in Sport. 6(1): 102-12.

Blackwell, J., E. Health, and C. Thompson. 2006. Effect of the Type 3 (oversize) tennis ball on physiological responses and play statistics during tennis play: Third world congress of science and racket sports.  Journal of Sports Sciences. 24(4): 333-53.

Brody, H. 1997. The physics of tennis III: The ball-racket interaction. American Journal of Physics. 65(10): 981-87.

Brody, H. 2003. Bounce of a tennis ball. Journal of Science and Medicine in Sport. 6(1):113-19.

Dragoo, J.L., and H.J. Braun. 2010. The effect of playing surface on injury rate. Sports Medicine. 40(1): 981-90.

Goodwill, S.R., S.B. Chin, and S.J. Haake. 2004. Wind tunnel testing of spinning and non-spinning tennis balls. Journal of Wind Engineering and Industrial Aerodynamics. 92:935-58.

Haake, S.J., S.G. Chadwick, R.J. Dignall, S. Goodwill, and P. Rose. 2000. Engineering tennis- slowing the game down. Sports Engineering. 3(2): 131-43.

IFT Tennis Technical Reference. (2012). Retrieved from http://www.itftennis.com/techical/equipment/balls/manufacture

Itf 2012 rules of tennis. (2012). Retrieved from http://www.itftennis.com/media/117960/117960.pdf

Lees, A. 2003. Science and the major rackets sports: a review. Journal of Sports Sciences. 21(9): 707-32.

Mehta, R.D. 1985. Aerodynamics of sports balls.  Annual Review of Fluid Mechanics. 17: 151-89.

Mehta, R.D., and J.M. Pallis. 2001. Sports ball aerodynamics: effects of velocity, spin and surface roughness. Structural Materials Division of the Minerals, Metals and Materials Society Symposium, Coronado, CA, April 22-25.

Miller, S. 2006. Modern tennis rackets, balls, and surfaces. British Journal of Sports Medicine. 40(5): 401-5.

Murias, J.M., D. Lanatta, C. R. Arcuri, and F.A. Laino. 2007. Metabolic and functional responses playing tennis on different surfaces. Journal of Strength and Conditioning Research. 21(1): 112-7.

Steele, C., R. Jones, and P.G. Leaney. 2006. Tennis ball fuzziness: assessing textile surface roughness using digital imaging. Measurement Science and Technology. 17:1446-55.

The Physics of Different Playing Surfaces (Basic)

Sports, such as tennis and golf, require athletes to be versatile on several different types of playing surface. These different course and court textures developed because of regional climate and resources available to the builders at the time.

Golf

The grass used in seeding a golf course depends on the climate where the course is located and the area of the golf course where it is used. For cooler areas such as the northern United States, bentgrass is used. This type of turf is used for fairways rather than the putting surface because it does not adapt well to being cut short. Bermuda grass is very common in the south because it thrives in the hot humid atmosphere. It can adapt to low mowing heights and thus can be used on tee boxes, greens, and fairways. In addition, Kentucky Blue grass can be used for fairways in most locations and zoysia grass is used in fairways. Finally, poa anna grass is perfect for the greens in cool damp climates such as Pebble Beach in Northern California.

Before starting a round, it is very important for a golfer to understand what surface he is playing on. The ball will act quite different on each type of surface. For example, a golfer is able to put more back spin on the ball in zoysia grass than he would Bermuda grass. This is because zoysia has a more firm blade that holds the ball higher allowing the golfer to strike the ball with more of the club’s surface area. When this increased surface area impacts the ball, more of the grooves on the club head grip the dimples on the ball and cause the additional spin. Back spin is important because it allows the golfer to stop the ball on a specific point on the green without rolling off.

The grass used for putting greens is extremely important for reading the movement of the ball and sinking the putt. Creeping bentgrass is the ideal surface for a green because it can be mowed very low and grows in a dense pack. It is necessary which way the grass is growing. This is also called the grain. The grain of a putting green depends on the movement of the sun, temperature, and water drainage on the green. A putt against the grain, meaning the grass is growing towards you, will be slower than a putt with the grass growing away from you because the grass will attempt to grab the ball, increasing the friction and slowing the ball speed. The grain can also increase the movement, or break, of a putt depending on the ball’s position on the green.

By: Kenny Morley, Ohio State University 

References:

Merritt, C. (2010). Comparison of Tennis Court Surfaces. Retrieved from http://www.livestrong.com/article/186749-comparison-of-tennis-court-surfaces/

Moorehouse, J. (2006). The Types of Grass and What It Means to Your Game. Retrieved from http://ezinearticles.com/?The-Types-of-Grass-and-What-It- Means-to-Your-Game&id=188396