Drag is the component of fluid force opposing an object's motion relative to the surrounding fluid. Surface pressure and viscous shear stress both contribute; their relative importance depends on shape and flow regime. A body can therefore experience drag even if most resistance comes from an uneven pressure field rather than direct tangential rubbing.
At low Reynolds number, the Stokes drag law gives for a sphere under its creeping-flow assumptions. In many inertial regimes, a useful representation is , with a measured or modeled drag coefficient . That coefficient can vary with Reynolds number, surface condition and geometry. Towing a body while measuring force at several speeds tests which regime applies. The supplied towing power is for steady motion along the drag direction.
In physics, drag refers to the resistance experienced by an object moving through a fluid, which can be a liquid or a gas. This force opposes the motion of the object and is often due to the viscosity of the fluid and the object's shape and speed. Drag is a critical factor in various fields, including aerodynamics, hydrodynamics, and engineering.
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