Rotation

Rotation is the circular movement of an object around a center (or point) of rotation. A three-dimensional object can always be rotated around an infinite number of imaginary lines called rotation axes (/ˈæksiːz/ AK-seez). If the axis passes through the body's center of mass, the body is said to rotate upon itself, or spin. A rotation about an external point, e.g. the Earth about the Sun, is called a revolution or orbital revolution, typically when it is produced by gravity.

Mathematics of rotation

Rotation in mathematics is a concept originating in geometry. Any rotation is a motion of a certain space that preserves at least one point. It can be described by a rotation matrix, a quaternion, a rotation vector, etc. Rotation of a point in two dimensions around the origin can be described by a rotation matrix, which can be parameterized by the angle of rotation θ.

Rotation in physics

In physics, rotation is a phenomenon occurring when an object spins around an axis. This can be clearly seen in the case of a spinning top. In an extended body, particles on the axis do not contribute to the angular momentum but particles far from the axis do, so the rotational inertia depends on the shape of the body.

Rotation in astronomy

In astronomy, rotation is a commonly observed phenomenon. Stars, planets and similar bodies all spin around on their axes. The rotation rate of planets in the solar system was first measured by tracking visual features. Stellar rotation is measured through Doppler shift or by tracking active surface features.

See also

• Angular velocity
• Centripetal force
• Torque
• Rigid body dynamics
• Rotational energy
• Rotational speed
• Rotational symmetry

References

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External links

• Example Website

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Rotation

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  Rotation Illustration
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  Axial Tilt Obliquity
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  Circular Motion vs Rotation
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  Precession
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