On the ability of drops or bubbles to stick to non-horizontal surfaces of solids

It is common knowledge that relatively small drops or bubbles have a tendency to stick to the surfaces of solids. Two specific problems are investigated: the shape of the largest drop or bubble that can remain attached to an inclined solid surface; and the shape and speed at which it moves along the surface when these conditions are exceeded. The slope of the fluid-fluid interface relative to the surface of the solid is assumed to be small, making it possible to obtain results using analytic techniques. It is shown that from both a physical and mathematical point of view contact-angle hysteresis , i.e. the ability of the position of the contact line to remain fixed as long as the value of the contact angle θ lies within the interval θ R [les ] θ [les ] θ A , where θ A [nequiv ] θ R , emerges as the single most important characteristic of the system.