# Formula Symbols - R

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

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 SymbolDefinitionUSMetric
$$L$$ - radiance - -
$$r \;or\; \rho$$ rho radial distance $$in\;or\;ft$$ $$mm\;or\;m$$
$$Q_e \;or\; W$$ - radiant energy - -
$$w$$ - radiant energy density - -
$$M$$ - radiant exitance - -
$$P \;or\; \Phi$$ Phi radiant flux - -
$$\phi$$ phi radiant flux density - -
$$I$$ - radiant intensity - -
$$P \;or\; \Phi$$ 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 $$ft$$ $$m$$
$$k \;or\; r$$ - radius of gyration $$ft$$ $$m$$
$$r_x$$ - 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 $$ft \;/\; sec^2$$ $$m \;/\; s^2$$
$$r$$ - ratio - -
$$k$$ - ratio of specific heat - -
$$a$$ - ratio of transformation - -
$$Ra$$ - Rayleigh number dimensionless number dimensionless number
$$X$$ - 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 - -
$$\mu$$ - reduced mass - -
$$p_r$$ - reduced pressure - -
$$\upsilon_r$$ upsilon reduced specific volume - -
$$T_r$$ - reduced temperature - -
$$\eta_r$$ eta reduced viscosity - -
$$\rho$$ rho reflectance - -
$$\tau$$ tau reflection coefficient - -
$$\rho$$ rho reflectivity - -
$$RF$$ - reheat factor - -
$$x$$ - relative abundance - -
$$a$$ - relative activity - -
$$A_r \;or\; M_r$$ - relative atomic mass - -
$$RD \;or\; d$$ - relative density dimensionless number dimensionless number
$$RH \;or\; \phi$$ phi relative humidity $$^\circ F$$ $$C$$
$$M_r$$ - relative molar mass - -
$$\mu_r$$ mu relative permeability - -
$$K$$ - relative permittivity - -
$$\alpha \;or\; \alpha_p$$ alpha relative pressure coefficient - -
$$k$$ - relative roughness $$in$$ $$mm$$
$$\eta_r$$ eta relative viscosity - -
$$E_r$$ - relativistic energy - -
$$m_r$$ - relativistic mass $$lbm$$ $$kg$$
$$p$$ - relativistic momentum - -
$$\tau$$ tau relaxation time - -
$$F_r$$ - removal factor - -
$$\rho_r$$ rho residual resestivity - -
$$R \;or\; \Omega$$ omega resistance $$ohm$$ $$ohm$$
$$K$$ - resistance coefficient - -
$$\phi$$ - 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 - -
$$\phi_v$$ - resistinance factor for shear in LRFD steel design - -
$$\phi_t$$ - resistinance factor for tension in LRFD steel design - -
$$\rho$$ rho resistivity - -
$$R$$ - resultant force $$lbf$$ $$N$$
$$Re$$ - Reynolds number dimensionless number dimensionless number
$$F_R$$ - Reynolds number factor - -
$$A$$ - Richardson constant - -
$$Ri$$ - Richardson number dimensionless number dimensionless number
$$R$$ - rigidity - -
$$C_{rr}$$ - rolling resistance dimensionless number dimensionless number
$$L_r$$ - roof live load in LRFD design - -
$$Ro$$ - Roshko number dimensionless number dimensionless number
$$Ro$$ - Rossby number dimensionless number dimensionless number
$$J \;or\; K$$ - 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 $$lbf-ft$$ $$N-m$$
$$n \;or\; \omega_{cyc}$$ omega rotational speed $$rpm$$ $$rad\;/\;s$$
$$k_r$$ - rotational spring constant $$lbf-ft \;/\; rad$$ $$N-m \;/\; rad$$
$$F$$ - rotational term - -
$$\omega$$ omega rotational velocity $$rad \;/\; sec$$ $$rad \;/\; s$$
$$R_{\infty}$$ infty Rydberg constant constant constant