  We describe the `Lie algebra of classical mechanics', modelled on the Lie
algebra generated by kinetic and potential energy of a simple mechanical system
with respect to the canonical Poisson bracket. It is a polynomially graded Lie
algebra, a class we introduce. We describe these Lie algebras, give an
algorithm to calculate the dimensions $c_n$ of the homogeneous subspaces of the
Lie algebra of classical mechanics, and determine the value of its entropy
$\lim_{n\to\infty} c_n^{1/n}$. It is $1.82542377420108...$, a fundamental
constant associated to classical mechanics.
