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The drag coefficient is a number which engineers use to model all of the complex dependencies of drag on shape and flow conditions. The drag coefficient Cd is equal to the drag D divided by the quantity: density r times reference area A times one half of the velocity V squared.

Cd = D / (.5 * r * V^2 * A)

Shape has a very large effect on the amount of drag produced. A flat plate has Cd = 1.28, a wedge shaped prism with the wedge facing downstream has Cd = 1.14, a sphere has a Cd that varies from .07 to .5, a bullet Cd = .295, and a typical airfoil Cd = .045.A typical value for the drag coefficient of a model rocket is .75, based on the cross-sectional area of the rocket. As shown above, this value can be reduced slightly by adding a fairing, or small cone, to the rear of the rocket between the body and the nozzle exit. Long thin rockets have less drag than short thick rockets.

Efficient drag-reduction design is needed by supercars, speedboats, and fighter-jets to travel at high-speeds.Usually, when a solid object moves through a liquid, the surrounding fluid molecules directly grip it, reducing the object's movement. For example, a submarine moving through the ocean needs energy to counteract these drag forces. A protective gas layer has been developed by some researchers so as to reduce these drag forces.They utilized a concept first described more than 250 years ago,the Leidenfrost effect. The effect is easily noticed when a drop of water skates around on a hot pan. The water moves around because liquid that's placed on a surface heated past a critical point generates an insulative gas layer, protecting the liquid from evaporating and allowing it to move around.The researchers inverted this centuries old observation to generate a drag-reducing gas layer around an object moving through liquid instead of dropping a liquid onto a heated surface, they dropped a heated surface into a liquid.