A specific instance of such a force that is associated with dynamic pressure is fluid resistance: a body force that resists the motion of an object through a fluid due to viscosity.
Spherical particles moving slowly in a viscous fluid encounter a resistance force, within the Stokes flow limit, to be derived as [ 25] (2) F drag = 6 π η a v, where η is the viscosity of the fluid, a is the radius of the particle, and v is the rotating velocity.
To reach this conclusion Newton had to show that (1) the inertia of the fluid does indeed produce a resistance force proportional to its density, a force that (2) is independent of the tenacity (that is, surface friction) and the friction of the parts (that is, viscosity) of the fluid.
Physically, a greater of β means a high dynamic viscosity (mu_{e}), which corresponds to porous medium and a small permeability for the porous medium, which causes the production of a resistance force to the fluid flow which causes a decrease for the velocity distribution when β increases and so enhances the temperature distribution along the thermal boundary layer as we can see from Figure 2.
When the particle charge is high enough, the electrical body force becomes increasingly strong to impede the fluid flow, thereby leading to a smaller resistance force compared to the perturbation result.
Other means include gravity, inertia, fluid resistance, and elastic resistance.
The classic example of fluid resistance training is swimming.
The fluid resistance in that case is water.
Because water is so dense, swimmers expend more than 90percentt of their energy just trying to overcome fluid resistance.
Fig. 10 Resistance force deference.
Air resistance force (F_{air}).
