Physics

Nothing can start spinning by itself

Pulling her arms in speeds a skater up because a system's total spin cannot change by itself. Mass moved closer to the axis makes her easier to turn, so her rate must rise. Sit on a swivel chair holding two books and pull them in: you speed up the same way.

Sources & further reading

OpenStax, Rice University11.3 Conservation of Angular Momentum (University Physics Volume 1)A free university physics textbook chapter on why a spinning body speeds up when it pulls its mass inward.Science, American Association for the Advancement of ScienceA Radio Pulsar Spinning at 716 HzThe paper announcing the fastest-spinning star ever found, turning 716 times every second.NASA Goddard Space Flight CenterMeasuring the Moon's Distance (Apollo Laser Ranging Experiments)NASA's page on the mirrors Apollo astronauts left on the Moon and what bouncing lasers off them has revealed.Proceedings of the Royal Society AMeasurement of the Earth's rotation: 720 BC to AD 2015A Royal Society study that used ancient eclipse records to measure how much Earth's day has stretched over 2,700 years.NASA ScienceOperating Hubble with Only One GyroscopeNASA's explanation of how Hubble aims itself and how it adapted after its steering gyroscopes started failing.Space Telescope Science InstituteNASA's Hubble Restarts Science in New Pointing ModeThe official announcement from the institute that runs Hubble, giving the dates of its switch to one-gyro pointing.NASANASA Ends Attempts to Fully Recover Kepler Spacecraft, Potential New Missions ConsideredNASA's press release explaining how two broken spinning wheels ended a planet-hunting telescope's main mission.U.S. Federal Aviation AdministrationRotorcraft Flying Handbook (FAA-H-8083-21)The FAA's official pilot handbook, which explains why every single-rotor helicopter needs a tail rotor.