Density

• $\rho =\frac{m}{V}$ is the density (or volumetric mass density or specific mass)
  • hebrew: צפיפות, צפיפות החומר, משקל סגולי, צפיפות המסה
  • SI unit: $kg/{\mathrm{m}}^3$, other units: $g/mL$ and $g/L$
• specific weight (or unit weight)
  • $\gamma =\frac{W}{V}=\rho g$
  • $W$ = weight, $V$ volume, $\rho$ density, $g$ standard gravity
• relative density (or specific gravity) (צפיפות יחסית) $\frac{{\rho }_{\text{substance}}}{{\rho }_{\text{reference}}}$ (dimensionless)
  • for liquids/solids: ${\rho }_{\text{reference}}$ is typically pure water at $4^{\circ }\text{C}$
  • for gases: ${\rho }_{\text{reference}}$ is typically air or hydrogen at a specified temperature