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  2. Friction - Wikipedia

    en.wikipedia.org/wiki/Friction

    If this frictional reaction force satisfies , then the tentative assumption was correct, and it is the actual frictional force. Otherwise, the friction force must be set equal to F f = μ N {\displaystyle F_{f}=\mu N} , and then the resulting force imbalance would then determine the acceleration associated with slipping.

  3. Perrin friction factors - Wikipedia

    en.wikipedia.org/wiki/Perrin_friction_factors

    The frictional coefficient is related to the diffusion constant D by the Einstein relation D = k B T f t o t {\displaystyle D={\frac {k_{B}T}{f_{tot}}}} Hence, f t o t {\displaystyle f_{tot}} can be measured directly using analytical ultracentrifugation , or indirectly using various methods to determine the diffusion constant (e.g., NMR and ...

  4. Darcy friction factor formulae - Wikipedia

    en.wikipedia.org/wiki/Darcy_friction_factor_formulae

    Churchill equation [24] (1977) is the only equation that can be evaluated for very slow flow (Reynolds number < 1), but the Cheng (2008), [25] and Bellos et al. (2018) [8] equations also return an approximately correct value for friction factor in the laminar flow region (Reynolds number < 2300). All of the others are for transitional and ...

  5. Stokes' law - Wikipedia

    en.wikipedia.org/wiki/Stokes'_law

    In fluid dynamics, Stokes' law gives the frictional force – also called drag force – exerted on spherical objects moving at very small Reynolds numbers in a viscous fluid. [1] It was derived by George Gabriel Stokes in 1851 by solving the Stokes flow limit for small Reynolds numbers of the Navier–Stokes equations. [2]

  6. Ergun equation - Wikipedia

    en.wikipedia.org/wiki/Ergun_equation

    The Ergun equation, derived by the Turkish chemical engineer Sabri Ergun in 1952, expresses the friction factor in a packed column as a function of the modified Reynolds number. Equation [ edit ]

  7. Darcy–Weisbach equation - Wikipedia

    en.wikipedia.org/wiki/Darcy–Weisbach_equation

    The equation is named after Henry Darcy and Julius Weisbach. Currently, there is no formula more accurate or universally applicable than the Darcy-Weisbach supplemented by the Moody diagram or Colebrook equation. [1] The Darcy–Weisbach equation contains a dimensionless friction factor, known as the Darcy friction factor. This is also ...

  8. Viscosity - Wikipedia

    en.wikipedia.org/wiki/Viscosity

    The pound and pound-force are equivalent; the two systems differ only in how force and mass are defined. In the BG system the pound is a basic unit from which the unit of mass (the slug ) is defined by Newton's Second Law , whereas in the EE system the units of force and mass (the pound-force and pound-mass respectively) are defined ...

  9. Free body diagram - Wikipedia

    en.wikipedia.org/wiki/Free_body_diagram

    Block on a ramp and corresponding free body diagram of the block.. In physics and engineering, a free body diagram (FBD; also called a force diagram) [1] is a graphical illustration used to visualize the applied forces, moments, and resulting reactions on a free body in a given condition.