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Rotation ○｜Definition｜1st｜20251119205401-00-⌔
Rotation
Rotation, also known as rotational motion or rotary motion, is the movement of an object that leaves at least one point unchanged. In 2 dimensions, a plane figure can rotate in either a clockwise or counterclockwise sense around a point called the center of rotation. In 3 dimensions, a solid figure rotates around an imaginary line called an axis of rotation.
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).1 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. A rotation around an axis completely external to the moving body is called a revolution (or orbit), as in a planetary orbit, e.g., Earth’s orbit around the Sun. The ends of the external axis of revolution can be called the orbital poles.1
Either 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).
Printed 2026-06-28.
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