✓ Sources checked · 10 September 2026 · View verification
Conservation of angular momentum means the total L of a chosen system remains unchanged when net external torque is zero. Its usefulness depends on the system boundary and reference origin.
By Matan · Updated
A reaction-wheel example
A spacecraft can exchange angular momentum internally with a reaction wheel. Consider an ideal one-axis spacecraft initially at rest. If its wheel gains +2 kg·m²/s and external torque is negligible, the rest of the spacecraft gains −2 kg·m²/s. With body inertia 10 kg·m², its angular velocity becomes −0.20 rad/s. This is an illustrative balance, not a mission measurement. [1]
Orbital angular momentum
For a particle, L = r × mv. About a fixed central force origin, torque vanishes because the force is radial. The transverse speed satisfies L = mrvtransverse. At general orbital points, total speed also includes a radial component; use the correct component when applying this relation.
Changing shape
For rotation about a suitable principal axis, L = Iω. Reducing inertia at conserved L increases spin rate, but the required internal work can change rotational kinetic energy. [1]
Precession involves torque
A supported spinning top under gravity can precess because torque changes the direction of its angular momentum. Conservation does not mean immunity to arbitrary external forces or torques. Separate that case from torque-free rotation.
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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 momentum conservation — Angular momentum conservation.
- OpenStax: Gyroscope precession — Gyroscope precession.
Cite this article
Matan. “Conservation of angular momentum.” Your Physicist. Originally published 2023-05-17; updated 2026-09-10. https://your-physicist.com/conservation-of-angular-momentum-2/
Revision history
: Added an internal angular-momentum exchange example and clarified orbital components and torque-driven precession. Added linked sources and a transparent verification record.
