Q6.12 Stop the earth, I want to get off! (T)
Does the construction of a high building slow down the rotation of the
earth?
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Solution
Yes – because the building work moves some of the matter in the
earth further from its axis of rotation. unless the building is at one of the
poles, this increases the earth’s moment of inertia about its axis
(very slightly!). No external torques can be generated by the building
work, since all the forces are internal, and the angular momentum of
the earth must therefore remain constant. If
L=Iω is constant and
I increases,
ω must decrease.