  We perform a dimension analysis for colliding viscoelastic spheres to show
that the coefficient of normal restitution $\epsilon$ depends on the impact
velocity g as \epsilon=1-\gamma_1g^{1/5}+\gamma_2g^{2/5}\mp..., in accordance
with recent findings. We develop a simple theory to find explicit expressions
for coefficients \gamma_1 and \gamma_2. Using these and few next expansion
coefficients for \epsilon(g) we construct a Pad\'e-approximation for this
function which may be used for a wide range of impact velocities where the
concept of the viscoelastic collision is valid. The obtained expression
reproduces quite accurately the existing experimental dependence \epsilon(g)
for ice particles.
