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KNOWLEDGE
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performance, how to maintain performance, how to make competition
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Aerodynamics,
Fluid Dynamics, and Friction
Air
Resistance, Clothing, and Drafting
In athletics
athletes must pass through air. This interaction with the air causes
the body to experience forces while in motion and during windy conditions.
The force that causes resistance to the body during performance is
called aerodynamic drag. Drag slows the forward motion of the body
or causes an increase in energy and force output by the athlete to
overcome the force of the air. Drag comes in two forms: friction drag
and form drag. Friction drag is caused by the movement of air over
the body’s surface. Form drag depends on the shape of the body.1
Athletes take counter measures to overcome friction drag and form
drag. Certain types of clothing can cut down on friction drag. Cotton
and fleece materials are made of fluffy fibers and loose matrixes.
This catches air and increases resistance. Thus athletes employ nylons
and polyesters which are comprised of sleek fibers and tightly woven
matrixes. This causes the material to be sleek and the air slides
off the clothing easily. During form drag athletes might take a certain
position or tuck to make the body more streamline. In certain positions,
such as a cyclist hunched over the handle bars, the flat chest is
not exposed, thus the chest is not acting as a parachute catching
the wind. This causes the cyclist to be more streamlined. In addition,
athletes will wear tight form fitting clothing in order to make the
body less resistant to air. Clothing that is loose and contains wrinkles
will act as a parachute. This will slow an athlete down.
Scientist have conducted wind tunnel test on clothing materials, hair,
shoes, and body positions. They have determined that it is possible
to lower the air resistance of an athlete by 0.5% to over 6% by improving
aerodynamics. One effective method of lowering air resistance is for
athletes to use the method of drafting. Drafting is a common technique
used by cyclist and runners. It reduces the aerodynamic drag on the
athlete that is traveling behind another athlete or athletes. The
athlete in front takes on the blunt of the air resistance. Thus, drafting
produces a wind shield for the athlete in back. This can reduce the
total energy output of the athlete in back or middle of the pack by
30% to 40% when compared to the athlete in front. It also must be
mentioned that air resistance plays less of a role at high altitudes
because the air is less dense.1
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Shaving
the Body in Sports
Skin friction
drag is the force caused by friction between molecules of air or water
and the skin. Reduction of skin friction drag is important in swimming
and running. Drag is minimized by reducing the roughness of the skin
which comes in contact with the water and air. This may be accomplished
by shaving the hair off the body so that it reduces the roughness
of the skin surface and provides a sleeker area for the water or wind
to move over. Thousands of tiny hairs cover the skin. These hairs
catch air and increase the water and air resistance. Many athletes
choose to shave in sports today to further reduce the drag affects
of hair. Races are won by thousandths of a second. Shaving may make
the difference between first and second place.
Note:
In swimming, warmer water will produce less drag on the surface of
the skin because cooler water is denser than warm water.
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Ball
Flight
Ball flight
is considered to be the path traveled by a ball. Ball flight can be
affected by four main variables. One variable is the surface of the
ball. That is, the stitches, groves, and sleekness of the external
material. Another variable is the weather. Humidity, wind, altitude,
and temperature may affect ball flight. Also ball flight can be affected
by the shape of the ball. Some balls are large, small, round, or oval.
Lastly rotations per second or revolutions per second of the ball
will affect the path in which it travels.
The surface of
most athletic balls is made of leather. However, other materials such
as pig skin and plastics may be used. The ball is usually made up
of multiple pieces of materials and must be stitched together. The
stitching process leaves depressed grooves and raised stitches on
the surface of the ball. These areas will increase the air resistance
at those specific locations, which will alter the path of the ball.
Some of the materials are sleek while others are not. Some surfaces
such as golf balls are pitted and other surfaces such as footballs
are raised. These have different functions such as the raised surface
of the football provides gripping by the hands. The shape of the ball
may affect its speed capabilities. A golf ball is smaller than a soccer
ball and thus produces less air resistance. This allows the golf ball
to reach greater speeds. Therefore, ball flight may be altered by
the surface of the ball. In addition, it must be noted that the surface
of a ball can become rough due to abrasions suffered during ground
impact. Sometimes the abrasions can increase air resistance and alter
ball flight characteristics.
Weather conditions can affect ball flight. A humid atmosphere is less
dense than a dry one at the same temperature and pressure. This provides
less air resistance. Also a humid environment may cause the stitches
on the ball’s surface to swell, providing more air resistance
over the swollen stitch. In addition at high altitudes the air is
less dense and provides less air resistance. This provides an optimal
environment for maximum speed and distance traveled by the ball. Wind
patterns and wind speed can also have an effect on ball flight. In
warm weather, the air is less dense than cooler air. This provides
for better flight capabilities.
The amount of revolutions per minute greatly affects ball flight.
When a ball rotates, one side of the ball experiences an decrease
in air resistance because one side of the ball is rotating away from
the direction of air flow (air flow and rotations are front to back).
The other side of the ball has an increase in air resistance because
air is flowing front to back, but the ball is rotating back to front.
This increase in air resistance on one side pushes the ball (Magnus
Effect). This causes the ball to take a curved path. Also the stitches
and grooves of a ball may catch air and increase the air resistance
on one side of the ball. This may cause a knuckle ball. In this instance
the ball’s flight path may curve, dive, and curve again. Soccer
players and baseball players use spin to there advantage when trying
to throw a strike or score a goal. Tennis players use topspin to push
the ball downward as it passes over the net. Golfers use back spin
to keep the ball in flight longer by providing a lifting affect. The
ability of athletes to use techniques to manipulate spin and thus
produce a wanted affect on the ball will make champions. When athletes
learn how to use weather to their advantage and master techniques
that produce varying ball flight paths, they will become successful
in their sport.
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The
Role of Friction in Winter Sports: Skating and Skiing
Winter sports are based on the gliding action of a skate or ski
over ice or snow. This gliding action produces friction. Friction
can be reduced by a lubricant or a low viscosity fluid. Some scientists
believe that when a ski or skate blade travels over the snow or ice
it causes heat due to friction. The same principle is used when one
rubs their hands together and heat is produced due to the skin rubbing
together. When the skate blade or ski becomes hot it melts the snow
or ice and produces a thin layer of water between the snow/ice and
ski/blade. Thus, the water produces a lubricant. The amount of snow
and ice that melts depends on two factors: the temperature of the
ski/blade and the distribution of the heat from the ski/blade to the
snow/ice. The greater the melting effect the better. Also the weather
plays a key role as well. Ice and snow temperatures may very with
the weather. Therefore, some athletes may gain an advantage during
competition due to shifts in temperature. Heating of blades and skis
decreases friction and improves performance. However, in some sports
and organizations, heating of blades and skis is forbidden. Equipment
temperatures may be taken prior to starting in some competitions.1
In skating, it has been calculated that friction between the blades
and ice is 35% higher on the curves than on the straights. Even small
changes in friction result in visible differences in performance.
A small increase in friction can increase a 500 m sprint time by 0.8
sec and in a 10,000 m race by 23.5 sec. A 0.8 sec difference in the
Olympic Games can mean the difference in being sixth place or winning
the gold medal.
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The
Role of Friction in Traction
Friction is a force that occurs when two surfaces move past one another.
In athletics, athletes use friction for traction. Shoe manufactures
design shoes to maximize traction so that athletes can stop, turn,
and propel themselves forward without losing their footing. This can
be both good and bad. Too much traction can cause injuries, while
not enough traction can cause injuries. Therefore, there is a fine
line between too much and too little traction in athletic performance.
The demands for traction vary from one sport to another. Also, varying
weather and playing surface conditions pose different demands for
traction. For instance, in soccer an athlete’s ability to make
a quick turn will depend on the amount of friction between the bottom
of the shoe and the field. In wet conditions the athlete may experience
a reduction in friction because of the water acting as a lubricant.
This predisposes the athlete to injury due to slipping or falling.
When choosing shoes, athletes should take into consideration the playing
surfaces and the amount of traction needed to effectively play on
those surfaces. On the same field of play athletes may need two different
types of shoes, one for wet conditions and one for dry conditions.
Traction greatly affects performance and athletes should consider
it during competition.
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