# principal axis

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## principal axis

[′prin·sə·pəl ′ak·səs]
(crystallography)
The longest axis in a crystal.
(engineering acoustics)
A reference direction for angular coordinates used in describing the directional characteristics of a transducer; it is usually an axis of structural symmetry or the direction of maximum response.
(mathematics)
One of a set of perpendicular axes such that a quadratic function can be written as a sum of squares of coordinates referred to these axes.
For a conic, a straight line that passes through the midpoints of all the chords perpendicular to it.
For a quadric surface, the intersection of two principal planes.
(mechanics)
One of three perpendicular axes in a rigid body such that the products of inertia about any two of them vanish.
(optics)

## principal axis

Primary axes
In the illustration on the left, line A is the principal axis while in the illustration on the right, line B is the principal axis. The moment of inertia is maximum around these axes in these two cases.
i. The lateral, vertical, and longitudinal axes.
ii. The axis of relative wind.
iii. The principal inertial axis: that line passing through the center of gravity in a plane of symmetry about which a long, slender body tends to rotate when rolling.
iv. A rectilinear axis in the plane of a cross section of a structural member about which the moment of inertia is the maximum.
References in periodicals archive ?
The component form of the constitutive model (26) with respect to the Lagrangian principal axes is
Events were considered to be stable if the standard deviation of at least one of the three principal axes was less than 4[degrees].
The results were nearly identical, so the simpler dichotomy, relating size and shape to the principal axes of the ancestral additive genetic covariance matrix, is reported here.
In order to give a complete description of material anisotropy, all three main yield stresses X, Y, Z and shear yield stresses R, S, T should be known according to the orientation of the principal axes of anisotropy.
In Lebanon, there are three principal axes of EU intervention and support in the field of human rights:
To get the RVSO, the principal axes of the single plumes boundaries are calculated, as the first principal axes meet in the VSO vicinity, the AVSO is the barycenter of these axes intersections.
For this polyimide film, the two principal axes coincided with the machine and transverse directions.
Version 8 is the first program that can calculate fatigue life from principal stresses rather than from individual components by resolving them into principal axes from a frequency response analysis.
They use an arbitrary axis for their operation, rather than being aligned with the principal axes.
For example, when the orthotropic material moves from the principal axes 1 and 2 to the turned axes 1' and 2' at the angle [omega] = 45[degrees], the strength criterion is presented in the following way
In this plane, wave front and energy flux coincide however for propagation along principal axes 1 and 3.

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