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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Hint

Is the angular momentum of the earth conserved? (Key Point 5.20)
 

Solution

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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.