# Formula Symbols - R

Written by Jerry Ratzlaff on . Posted in Nomenclature & Symbols for Engineering, Mathematics, and Science

## Formula Symbols - R

For other symbols see:  A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

SymbolGreek SymbolDefinitionUSMetricValue
$$L$$ - radiance - -  -
$$r$$, $$\;\rho$$ rho radial distance $$in\;or\;ft$$ $$mm\;or\;m$$  -
$$Q_e$$, $$\;W$$ - radiant energy - -  -
$$w$$ - radiant energy density - -  -
$$M$$ - radiant exitance - -  -
$$P$$, $$\;\Phi$$ Phi radiant flux - -  -
$$\phi$$ phi radiant flux density - -  -
$$I$$ - radiant intensity - -  -
$$P$$, $$\;\Phi$$ Phi radiant power - -  -
$$Q_r$$ - radiant heat - -  -
$$r$$ - radius $$in\;or\;ft$$ $$mm\;or\;m$$  -
$$r$$ - radius of a circle $$in\;or\;ft$$ $$mm\;or\;m$$  -
$$r$$ - radius of a circular path $$ft$$ $$m$$  -
$$\rho$$ rho radius of curvature $$in$$ $$mm$$  -
$$R$$ - radius of curvature of a beam $$ft$$ $$m$$  -
$$k$$, $$\;r$$ - radius of gyration $$in\;or\;ft$$ $$mm\;or\;m$$  -
$$r_x$$ - radius of gyration with respect to an x-axis $$in$$ $$mm$$  -
$$r_y$$ - radius of gyration with respect to an y-axis $$in$$ $$mm$$  -
$$R$$ - range $$ft$$ $$m$$  -
$$k$$ - rate coefficient - -  -
$$a_c$$ - rate of change in acceleration $$ft \;/\; sec^2$$ $$m \;/\; s^2$$  -
$$N$$ - rate of rotation $$rpm$$ $$rpm$$  -
$$x_t$$ - rated pressure drop ratio factor dimensionless dimensionless  -
$$r$$ - ratio - -  -
$$\gamma$$, $$\;\kappa$$, $$\;k$$ gamma, kappa ratio of specific heat dimensionless dimensionless  -
$$F_k$$ - ratio of specific heat factor dimensionless dimensionless  -
$$a$$ - ratio of transformation - -  -
$$Ra$$ - Rayleigh number dimensionless dimensionless  -
$$X$$ - reactance - -  -
$$R$$ - reaction $$lbf$$ $$N$$  -
$$Q$$ - reaction energy - -  -
$$R$$ - reaction force $$lbf$$ $$N$$  -
$$R$$ - reaction load at bearing point $$lbf$$ $$N$$  -
$$\alpha$$ alpha recombination coefficient - -  -
$$z$$ - reduced activity - -  -
$$g'$$ - reduced gravity $$ft\;/\;sec^2$$ $$m\;/\;s^2$$ -
$$\mu$$ - reduced mass - -  -
$$h$$ - reduced Plank constant constant constant $$1.054\;571\;817...\;x\;10^{-34}\;J\;s$$
$$p_r$$ - reduced pressure $$lb\;/\;in^2 \;or\; psi$$ $$Pa$$  -
$$\upsilon_r$$ upsilon reduced specific volume - -  -
$$T_r$$ - reduced temperature $$^\circ F$$ $$C$$  -
$$\eta_r$$, $$\;\mu_r$$ eta, mu reduced viscosity $$lbf-sec/ft^2$$ $$Pa-s$$  -
$$\rho$$ rho reflectance - -  -
$$\tau$$ tau reflection coefficient - -  -
$$\rho$$ rho reflectivity - -  -
$$RF$$ - reheat factor - -  -
$$x$$ - relative abundance - -  -
$$a$$ - relative activity - -  -
$$A_r$$, $$\;M_r$$ - relative atomic mass - -  -
$$RD$$, $$\;d$$ - relative density dimensionless dimensionless  -
$$RH$$, $$\;\phi$$ phi relative humidity $$^\circ F$$ $$C$$  -
$$M_r$$ - relative molar mass - -  -
$$\mu_r$$ mu relative permeability - -  -
$$K$$ - relative permittivity - -  -
$$\alpha$$, $$\;\alpha_p$$ alpha relative pressure coefficient - -  -
$$k$$ - relative roughness $$in$$ $$mm$$  -
$$\eta_r$$ eta relative viscosity $$lbf-sec/ft^2$$ $$Pa-s$$  -
$$\eta_i$$, $$\;\mu_i$$ eta, mu relative viscosity increment $$lbf-sec/ft^2$$ $$Pa-s$$  -
$$E_r$$ - relativistic energy - -  -
$$m_r$$ - relativistic mass $$lbm$$ $$kg$$  -
$$p$$ - relativistic momentum - -  -
$$\tau$$ tau relaxation time - -  -
$$F_r$$ - removal factor - -  -
$$\rho_r$$ rho residual resestivity - -  -
$$R$$, $$\;\Omega$$ omega resistance $$ohm$$ $$ohm$$  -
$$K$$ - resistance coefficient dimensionless dimensionless  -
$$K$$ - resistance coefficient for fittings and valves dimensionless dimensionless  -
$$\phi$$ - resistinance factor for LRFD steel design - -  -
$$\phi_c$$ - resistinance factor for compression in LRFD steel design - -  -
$$\phi_b$$ - resistinance factor for flexure in LRFD steel design - -rest mass  -
$$\phi_v$$ - resistinance factor for shear in LRFD steel design - -  -
$$\phi_t$$ - resistinance factor for tension in LRFD steel design - -  -
$$\rho$$ rho resistivity - -  -
$$E_0$$ - rest energy $$ft-lbf$$ $$J$$  -
$$m_0$$ - rest mass $$lbm$$ $$kg$$  -
$$R$$ - resultant force $$lbf$$ $$N$$  -
$$rpm$$ - revolutions per minute - -  -
$$Re$$ - Reynolds number dimensionless dimensionless  -
$$F_r$$ - Reynolds number factor dimensionless dimensionless  -
$$A$$ - Richardson constant constant constant  $$1.20173\;x\;10^6\;A\;m^{-2}\;K^{-2}$$
$$Ri$$ - Richardson number dimensionless dimensionless  -
$$R$$ - rigidity - -  -
$$C_{rr}$$ - rolling resistance coefficient dimensionless dimensionless  -
$$L_r$$ - roof live load in LRFD design - -  -
$$Ro$$ - Roshko number dimensionless dimensionless  -
$$Ro$$ - Rossby number dimensionless dimensionless  -
$$Fr_r$$ - Rotating Froude number dimensionless dimensionless  -
$$J$$, $$\;K$$ - rotational - -  -
$$\alpha$$ alpha rotational acceleration $$rad \;/\; sec^2$$ $$rad \;/\; s^2$$  -
$$C_r$$ - rotational dampening coefficient $$lbf-ft-sec \;/\; rad$$ $$N-m-s \;/\; rad$$  -
$$\tau$$ tau rotational force $$lbf-ft$$ $$N-m$$  -
$$KE_r$$ - rotational kinetic energy - - -
$$n$$, $$\;\omega_{cyc}$$ omega rotational speed $$rpm$$ $$rad\;/\;s$$  -
$$k_r$$ - rotational spring constant $$lbf-ft \;/\; rad$$ $$N-m \;/\; rad$$  -
$$k$$ - rotational stiffness $$lbf-ft \;/\; rad$$ $$N-m \;/\; rad$$  -
$$F$$ - rotational term - -  -
$$\omega$$ omega rotational velocity $$rad \;/\; sec$$ $$rad \;/\; s$$  -
$$n$$ - roughness coefficient - -  -
$$P$$, $$\;Z$$ - Rouse number dimensionless dimensionless  -
$$R_{\infty}$$ infty Rydberg constant constant constant $$10\;973\;731.568\;160\;x\;m^{-1}$$