Lithium be cut with a knife. When cut, it possesses a silvery-white color that quickly changes to gray as it oxidizes to lithium oxide. While it has one of the lowest melting points among all metals (180 °C), it has the highest melting and boiling points of the alkali metals. Lithium has a very low density (0.534 g/cm), comparable with pine wood. It is the least dense of all elements that are solids at room temperature; the next lightest solid element (potassium, at 0.862 g/cm) is more than 60% denser. Furthermore, apart from helium and hydrogen, it is less dense than
Gauss's principle of least constraint kinetic energy formula_10 is also conserved under these conditions Since the line element formula_12 in the formula_13-dimensional space of the coordinates is defined the conservation of energy may also be written Dividing formula_16 by formula_17 yields another minimal quantity Since formula_19 is the local curvature of the trajectory in the formula_13-dimensional space of the coordinates, minimization of formula_21 is equivalent to finding the trajectory of least curvature (a geodesic) that is consistent with the constraints. Hertz's principle is also a special case of Jacobi's formulation of the least-action principle. Gauss's principle of least constraint The principle of least constraint is