Question

Strictly speaking, as more and more skyscrapers are built on the surface of the Earth, does the day tend to become longer or shorter? And strictly speaking, does the falling of autumn leaves tend to lengthen or shorten the 24-hour day? What physical principle supports your answers?

Answer 1

lengthen; shorten; conservation of angular momentum

Step-by-step explanation:

speed of rotation is always constant when the net torque acting on the system is zero

Answer 2

Assume that the planet has a defined angular momentum (this is not true due to tidal friction). So if mass is farther away from the center of mass it will have more angular momentum, and if mass is near you will have more angular momentum.

If the mass is similar to the center of mass and slower if the mass is farther from the center of mass, an object will spin faster to combat this. Building skyscraper will also slow down the earth and dropping leaves will raise the angular velocity.

A great example of this is with figure skaters, when they want to spin faster they tuck themselves in tightly, bringing more mass close to the center of mass which increases angular velocity there.