✓ Sources checked · 10 September 2026 · View verification
Rotational motion changes a body’s orientation. In fixed-axis rigid rotation, all points share angular velocity, while linear speed increases with distance from the axis.
By Matan · Updated
Angle, speed and acceleration
Angular displacement is measured in radians, angular velocity ω in rad/s and angular acceleration α in rad/s². At distance r from a fixed axis, tangential speed is r|ω|, tangential acceleration is rα and inward acceleration is rω². [1]
Worked rotating disk
A disk turns steadily at 60 rpm, or 2π rad/s. At radius 0.10 m, speed is 0.628 m/s and inward acceleration 3.95 m/s². At radius 0.20 m, both are twice as large: 1.26 m/s and 7.90 m/s². Angular velocity remains the same for both points.
Rotation plus translation
A wheel rolling without slip combines translation of its centre with rotation. Its centre speed obeys vcm = R|ω|. Relative to the ground, rim points do not simply follow circles about a stationary centre. Orbiting and rotating are also distinct descriptions.
What changes the spin?
Net torque changes angular momentum. With negligible external torque, a suitable change of inertia can change spin rate while conserving angular momentum. Existing rotation itself does not prove a nonzero net torque. [2]
Know when the axis changes
General tumbling requires a vector and inertia-tensor treatment. The disk example assumes a rigid body about a fixed axis and is not a model for every spinning object.
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How this article was checked
Sources checked; calculations checked where shown. The definitions, model assumptions and main explanatory claims were cross-checked against the sources below. Worked-example arithmetic and units were checked separately. These examples are illustrative calculations, not experimental measurements.
Source cross-check and editing assisted by AI. No independent human scientific review is recorded for this revision. The check applies to the version dated 10 September 2026; it is not a guarantee that every possible interpretation is correct.
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Sources and further reading
- OpenStax: Angular and linear quantities — Angular and linear quantities.
- OpenStax: Angular momentum conservation — Angular momentum conservation.
Cite this article
Matan. “Rotational Motion Made Simple.” Your Physicist. Originally published 2026-06-11; updated 2026-09-10. https://your-physicist.com/rotational-motion-made-simple/
Revision history
: Added checked radius-dependent speeds and accelerations; clarified torque, rolling and changing axes. Added linked sources and a transparent verification record.
