Streamlining reduces air resistance by providing a smooth surface over which air flows easily and uniformly. Without streamlining, eddies formed on the trailing edges of objects create turbulent, low-pressure areas and increase air resistance, also known as drag.
Streamlining allows objects to move more efficiently through the air by parting the air ahead of them and allowing it to recombine as the objects pass, according to Science Learning Hub. The typical teardrop shape is an example of streamlining in which the air is allowed to slip back together smoothly in the wake of the object. The teardrop shape keeps the flow of air close to the surface at all times, resulting in a smooth recombination of the air displaced. Other shapes, such as circles, force the oncoming air upward as it moves towards the trailing edge. This not only creates eddies, but also disrupts the flow of air above the surface, further increasing aerodynamic drag.
Streamlining is very apparent within the sport of cycling and in the design of airplanes and modern automobiles. The streamlined shapes of planes and vehicles take advantage of the lowered air resistance to reduce fuel consumption. In the same way, a cyclist with a teardrop-shaped helmet crouches down to allow the air to slip over him smoothly and recombine, increasing his speed.