... planes Two planes in 3‐dimensional space are perpendicular if normals to the two planes are perpendicular. If n 1 and n 2 are vectors normal to the planes, this is so if n 1 . n 2...

Two planes in 3-dimensional space are perpendicular if normals to the two planes are perpendicular. If n 1 and n 2 are vectors normal to the planes, this is so if n 1 . n 2=0.

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...sheet needs to be identified; the orientation of chain lines in bound, laid paper helps determine this ( see format ). In a sheet folded in half, the chain lines run parallel to the fold and book spine, producing a *folio . A second fold, perpendicular to the first, will produce chain lines running perpendicular to the spine, and thus a *quarto . A third fold restores the original orientation, producing an *octavo , and so on. Once a single sheet has been identified, any watermark and countermark can be noted, and their relative positions in the sheet...

The distance from a point to a line or plane measured along the line perpendicular to the line or plane which passes through the given point. It will be the shortest distance between the point and ...

(to a plane)A vector whose direction is perpendicular to the plane. A normal vector is perpendicular to any vector whose direction lies in the plane.

At right angles to one another. Can be of two lines, two planes, a line and a plane, or a line and a surface.

The plane that is perpendicular to the optical axis of a lens and that passes through the optical centre. A thick lens has two principal planes, each passing through a principal point.

Let P be a point on a smooth surface. The tangent at P to any curve through P on the surface is called a tangent line at P, and the tangent lines are all perpendicular to a line through P called the ...

A fixed plane passing through the centre of mass of the Solar System, and oriented perpendicular to the axis about which the angular momentum of the Solar System is measured. The invariable plane is ...

The stress which acts perpendicularly to the plane to which a force has been applied. Normal compressive stresses (with positive values) inhibit sliding along a plane; normal tensile stresses (with ...

The direction perpendicular to a given plane, such as the plane of the Earth's equator or the plane of the ecliptic. For a rotating body, the poles lie at the ends of the body's axis of rotation. See ...

In coordinate geometry of the plane, a useful necessary and sufficient condition that two lines, with gradients m 1 and m 2, are perpendicular is that m 1 m 2=−1. (This is taken to include the cases ...

Compounds that contain the group >C=C=C<, in which three carbon atoms are linked by two adjacent double bonds. The outer carbon atoms are each linked to two other atoms or groups by single bonds. The ...

A system for categorizing symmetries of molecules. Cn groups contain only an n-fold rotation axis. Cnv groups, in addition to the n-fold rotation axis, have a mirror plane that contains the axis of ...

(of the plane)Let l be a line in the plane. Then the mirror-image of a point P is the point P′ such that PP′ is perpendicular to l and l cuts PP′ at its midpoint. The reflection of the plane in the ...

An imaginary line (one of the anatomical reference axes) running down the centre of the body perpendicular to the transverse plane, around which rotations in the transverse plane (e.g. a body spin ...

The dip of the trace of a plane, which is measured from the horizontal in any section non-perpendicular to the strike of the plane. Compare true dip. See also dip, angle of.

The following theorem about moments of inertia of a lamina:TheoremSuppose that a rigid body is in the form of a lamina lying in the plane z=0. Let I 0x, I 0y and I 0z be the moments of inertia of the ...

A zone of a sphere is the part between two parallel planes. If the sphere has radius r and the distance between the planes is h, the area of the curved surface of the zone equals 2π rh.A ...

The stress produced by forces acting on a unit area of rock, which can be resolved into a normal stress and a shear stress, acting perpendicularly and parallel to a plane respectively. Compressive ...