An angle of incidence is the angle between a beam incident on a surface and the normal (line perpendicular to the surface at the point of incidence). The beam can be formed by any wave: optical, acoustical, microwave, X-ray etc. In Fig.1 the red line representing a ray makes an angle θ with the normal (dotted line).
Another common usage is in aviation, where it refers to the angle between the wing's chord (aircraft) and the longitudinal axis of an aircraft (a fixed value). Fig.2 shows a side view of part of an aeroplane. The wing (dotted blue line) makes an angle a with the fuselage (solid blue line). The wings are typically mounted at a small positive angle of incidence, to allow the fuselage to be "flat" to the airflow in normal cruising flight. Angles of incidence of about 6° are common on most general aviation designs. Another term for angle of incidence in this context is rigging angle. It should not be confused with the angle of attack, which is the angle the wing chord presents to the airflow in flight. Note that some ambiguity in this terminology exists, as some engineering texts that focus solely on the study of airfoils and their medium may use either term when referring to angle of attack.
An angle of incidence is the angle between a beam incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal.
The angle of incidence at which light is first totally internally reflected is known as the critical angle.
It should not be confused with the angle of attack, which is the angle the wing chord presents to the airflow in flight.
Running rigging is the term for the rigging of a sailing vessel that is used for raising, lowering and controlling the sails - as opposed to the standing rigging, which supports the mast and other spars.
Traditionally the running rigging was easily recognized, since for flexibility it was not coated with tar and therefore of a light color, while the standing rigging was tarred for protection and therefore fl or dark in color.
On modern vessels, running rigging is likely to be made from nylon and other synthetic fibers, while the standing rigging is frequently made of steel cable, for strength.
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