  In 1805, Young was the first who introduced an expression for contact angle
in static, but today, the motion of the contact-line formed at the intersection
of two immiscible fluids and a solid is still subject to dispute. By means of
the new physical concept of line viscosity, the equations of motions and
boundary conditions for fluids in contact on a solid surface together with
interface and contact-line are revisited. A new Young-Dupr\'e equation for the
dynamic contact angle is deduced. The interfacial energies between fluids and
solid take into account the chemical heterogeneities and the solid surface
roughness. A scaling analysis of the microscopic law associated with the
Young-Dupr\'e dynamic equation allows us to obtain a new macroscopic equation
for the motion of the contact-line. Here we show that our theoretical
predictions fit perfectly together with the contact angle hysteresis phenomenon
and the experimentally well-known results expressing the dependence of the
dynamic contact angle on the celerity of the contact-line. We additively get a
quantitative explanation for the maximum speed of wetting (and dewetting).
