alleryStart learning →What keeps Earth turning, and what is slowly changing its rate of spin?
ANothing acts on it, so the rate never changes
BSolar wind torque, which slowly speeds it up
CIts own weight, which slowly speeds it up
DAlmost no torque acts, but tides slow it down
Answer & Solution
Correct answer: D. Almost no torque acts, but tides slow it down
1. Changing angular momentum needs a torque acting over time, since delta L = (net tau) delta t.
2. Earth has an enormous angular momentum, so a large torque acting for a long time is needed to alter it.
3. Only the tides exert a significant retarding torque, and even that acts very slowly.
4. So Earth keeps spinning and will do so for billions of years, though ever more slowly.
5. Saying nothing acts on it at all overstates the case, since the tidal torque is real if tiny.
_Source: OpenStax College Physics (CC BY 4.0), Ch 10 "Rotational Motion and Angular Momentum", section 10.5 Angular Momentum and Its Conservation_
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