That is to say, any spatial rotation can be decomposed into a combination of principal rotations.įurther information: Rotations in two dimensionsĢ-dimensional rotations, unlike the 3-dimensional ones, possess no axis of rotation, only a point about which the rotation occurs. Rotation around any axis can be performed by taking a rotation around the x axis, followed by a rotation around the y axis, and followed by a rotation around the z axis. Rotations around the x, y and z axes are called principal rotations. However, a rotation around a point or axis and a rotation around a different point/axis may result in something other than a rotation, e.g. Thus, the rotations around a point/axis form a group. The reverse ( inverse) of a rotation is also a rotation. If a rotation around a point or axis is followed by a second rotation around the same point/axis, a third rotation results. The axis is perpendicular to the plane of the motion. That common point lies within the axis of that motion. This definition applies to rotations in two dimensions (in a plane), in which exactly one point is kept fixed and also in three dimensions (in space), in which additional points may be kept fixed (as in rotation around a fixed axis, as infinite line).Īll rigid body movements are rotations, translations, or combinations of the two.Ī rotation is simply a progressive radial orientation to a common point. Mathematically, a rotation is a rigid body movement which, unlike a translation, keeps at least one point fixed. Main article: Rotation (mathematics) Rotation ( angular displacement) of a planar figure around a point Rotational orbit v spin Relations between rotation axis, plane of orbit and axial tilt (for Earth) Įither type of rotation is involved in a corresponding type of angular velocity (spin angular velocity and orbital angular velocity) and angular momentum (spin angular momentum and orbital angular momentum). The ends of the external axis of revolution can be called the orbital poles. In that case, the surface intersection of the internal spin axis can be called a pole for example, Earth's rotation defines the geographical poles.Ī rotation around an axis completely external to the moving body is called a revolution (or orbit), e.g. The special case of a rotation with an internal axis passing through the body's own center of mass is known as a spin (or autorotation). A solid figure has an infinite number of possible axes and angles of rotation, including chaotic rotation (between arbitrary orientations), in contrast to rotation around a fixed axis. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersecting anywhere inside or outside the figure at a center of rotation. Rotation or rotational motion is the circular movement of an object around a central line, known as axis of rotation.
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