Final answer:
The angle between the long axis of an object and the direction of fluid flowing past is known as the contact angle. It is an important concept in fluid dynamics, determining whether a liquid will spread out or bead up on a surface.
Step-by-step explanation:
It is the angle between the tangent to the liquid surface and the surface of the object. The contact angle is an important concept in fluid dynamics, particularly in the study of wetting and surface tension. It determines whether a liquid will spread out or bead up on the surface of an object.
For example, if the contact angle is close to 0 degrees, the liquid will spread out and wet the surface. If the contact angle is close to 180 degrees, the liquid will bead up and not wet the surface.