Air resistance is an opposing force often known as drag force. Air resistance acts in the opposite direction to snow skier’s velocity and can either harm or enhance performance of the athlete. The flow of air around an object causes the unavoidable effect of drag and is influenced by the size, shape, surface, and overall speed of an object (John Polson, 2013). Air resistance is present in snow skiers and can inhibit their performance in a race greatly if the proper precautions and positions are not met. Three of the main aspects of snow skiing are posture, clothing and location; all of which are affected by air resistance.
The drag force of an object is influenced by size, shape surface area and velocity of the object. The force of drag is inversely proportional to the velocity of a skier, therefore the skier needs to minimise the drag force to increase their speed. To calculate drag force the equation F_D=1/2 CpAv^2 is given; where C is the drag co efficient of the object, p is the air density in kilograms per cubic metre (kgm-3), A is the frontal area of the object in squared metres (m2) which is perpendicular to v, which is the velocity of the skier (Normani F 2009).
The drag coefficient pertains to the shape of the object and its surface area, for example the larger the direct frontal surface area the larger the drag coefficient, which in turn equates to a larger drag force acting upon the skier. The drag coefficient is the ratio of the drag on a body moving through air to the product of the velocity and surface area of the body (Random House Inc. 2015). The drag coefficient can be found by rearranging the drag force equation to get C_D=D/(0. 5pv^2 A).
Where D is the drag force measured in Newtons (N), p is the air density in kilograms per cubic metre (kgm-3), v is velocity in metres per second (ms-1) and A is frontal surface area measured in squared metres (m2). The diagram below shows the general drag coefficients of basic shapes. To minimise the force of drag on the skier a streamlined body shape would create the least amount of drag force possible. When applied practically to a snow skier the minimising of drag force through the drag force equation can be shown in the different body positions such as the tuck.
The tuck is one position that is used to reduce air resistance. The tuck is when the skier crouches down into and egg shape with their arms pulled in, a flat back with legs that are spread apart and their head facing downwards. This position is useful as the frontal surface area of the skier is reduced. The air resistance acts around the person which minimises the drag force acting upon the person. The diagrams below show the effects of body positions on air resistance and movement around the objects.
Figure 2 is a picture of a snow skier in the tuck position, whereas on the right the picture shows a person skiing in an upright position. In the picture on the left the majority of the air resistance is going over the person, creating a slip stream of air that allows the skier to glide through the air. Figure 3 shows the drag force being maximised by the increased frontal surface area of the skier, which is in turn decreasing his velocity. Clothing is a big influence in aerodynamic drag and the performance of a skier.
The clothing of the skier affects the drag force impacting on the skier. Typically in professional snow skiing tight suits are worn with thermal materials to keep the skier warm and to avoid bulk, as bulkier clothing creates greater force of drag due to a greater surface area on the person. The tight clothing, create a reduced frontal surface area, which reduces the drag force of the object. Figure 4 demonstrates the slip stream of air resistance around objects with different frontal surface areas.
The diagram displays that the bulkier and taller increased frontal surface area of the object creates high amounts of drag because of the flow of air around and behind the object. The aerofoil shape is the most effective shape to reduce air resistance as the flow of air around the shape minimises drag. A skier would want to create the same effect as the aerofoil shape to increase velocity, which is conducted through the use of tight clothing and body positions such as the tuck.
Air resistance is not the same in all places of the world, so performance can either be enhanced or harmed from the place of training and the place of competition. Experts hypothesised that for the Sochi 2014 winter Olympics no new world records would be set due to the high amounts of air resistance (Gorski C 2014). Sochi is located at sea level, meaning that the air density would be very high. This inhibited the athletes’ performance as a greater drag force would have impacted them as the air resistance is directly proportional to the force of drag in the drag equation; F_D=1/2 CpAv^2.
Chris Gorski (2014) says that the majority of Olympic records were set 12 years ago, in Salt Lake City, Utah because of the low air density on the tracks. The tracks that the records were set sat around 1. 4 kilometres above sea level. The difference in the height of the tracks, that skiers perform on affect their performances greatly especially because of the lack of consistency of the tracks.
This would affect their performance because air density is one of the main mpacting factors on drag force. In conclusion air resistance affects the performance of skiers in many aspects such as body position, body movement, clothing, equipment and location but the main factors are the drag coefficient, air density, the projected frontal area and velocity of the skier. These impacts can be shown by the drag force equation F_D=1/2 CpAv^2, where velocity is inversely proportional to drag force.