Skin friction drag is the drag between surface and water. Pressure drag is the resistance generated due to differential pressure along the swimmer body.

n. Drag caused by increased pressure on the front and decreased pressure on the rear of an object moving through a fluid medium such as air or water or of a stationary object around which the medium passes.

Surface Drag: Drag force acting on an object within a fluid and caused by friction between the fluid and the surface of the object. Form Drag: Drag force acting on an object within a fluid and caused by the impact forces of the fluid molecules with the object.

Types of drag are generally divided into the following categories:

• parasitic drag, consisting of. form drag, skin friction drag,
• lift-induced drag, and.
• wave drag (aerodynamics) or wave resistance (ship hydrodynamics).

As speed increases, the induced drag decreases, but parasitic drag increases because the fluid is striking the object with greater force, and is moving across the object’s surfaces at higher speed. Each of these drag components changes in proportion to the others based on speed.

As airspeed increases, parasite drag increases, while induced drag decreases. Profile drag remains relatively constant throughout the speed range with some increase at higher airspeeds.

Profile drag is reduced through the use of natural laminar flow airfoils, which maintain distinct low-drag-ranges (drag buckets) surrounding design lift values. The low-drag-ranges can be extended to include off-design values through small flap deflections, similar to cruise flaps.

The size of the lift force Lift must be equal to weight in level flight so induced drag will depend on the weight of the aircraft. Induced drag will be greater at higher aircraft weights.

To estimate the total parasite drag Do, it is commonly assumed that it is simply a summation of the estimated parasite drags of the various drag-producing components on the aircraft. For example, Do = Dfuselage + Dtail + Dgear + …

The drag equation states that drag D is equal to the drag coefficient Cd times the density r times half of the velocity V squared times the reference area A. For given air conditions, shape, and inclination of the object, we must determine a value for Cd to determine drag.

Parasite Drag is caused by moving a solid object through a fluid medium. In aerodynamics, the fluid medium concerned is the atmosphere. The principal components of Parasite Drag are Form Drag, Friction Drag and Interference Drag.

There are three types of parasite drag: form drag, interference drag, and skin friction.

Skin friction is the type of parasite drag that is most difficult to reduce. No surface is perfectly smooth. Even machined surfaces, when inspected through magnification, have a ragged, uneven appearance. This rough surface will deflect the streamlines of air on the surface, causing resistance to smooth airflow.

Drag is influenced by other factors including shape, texture, viscosity (which results in viscous drag or skin friction ), compressibility, lift (which causes induced drag ), boundary layer separation, and so on.

Does Drag Increase with Speed? As an aircraft’s speed increases, drag on the aircraft generally increases much faster. Doubling the speed makes the airplane encounter twice as much air moving twice as fast, causing drag to quadruple. Drag, therefore, sets practical limits on the speed of an aircraft.

Like friction, the drag force always opposes the motion of an object. Unlike simple friction, the drag force is proportional to some function of the velocity of the object in that fluid.