air resistance

(mechanics) Wind drag giving rise to forces and wear on buildings and other structures.

Air resistance is the enemy common to all runners and cyclists. Air produces frictional forces which tend to reduce the speed of anyone moving through it. About eight per cent of a runner's energy is expended in overcoming air resistance, but up to 80 per cent of that energy can be saved by drafting (running directly behind another runner). During cycling even greater savings of energy can be made. The larger the group of cyclists and the further from the front the cyclist rides, the greater the energy saved. This is why it is much easier to ride towards the back of the peloton in the Tour de France, than to ride at the head of the race.

A frictional force, which tends to remove the speed of a body moving through air and cause the body to fall to the ground before it has completed its parabolic flight path. Air resistance increases with speed and lightness of the body. It is also increased by motions, such as the quivering of an arrow, the spinning of a ball, or the flapping of shoe laces, when the motions are in a direction other than that of the whole body. Air resistance is affected by the surface covering and shape of the body (see streamlining). See also drafting, drag, fluid resistance.