Collapsing of an underwater bridge
A massive underwater bridge is about to collapse and fall to the bottom of the ocean. While the this could cause a terrible tsunami, experts are also worried about a slight change in the length of the day. Will this cause the Earth's day to become longer or shorter, even by a small amount?
How does this at all relate to the length of a day?
Answer
The Earth is rotating because it has angular momentum. When an event such as a bridge collapse occurs, the distribution of mass on Earth changes, but the total angular momentum is conserved.
Consider the equation L = I ω. The angular momentum L is conserved, but the moment of inertia I has changed. We know that moment of inertia is greatest when the mass is distributed closer to the axis of rotation.If an underwater bridge collapses and falls, does this increase or decrease the moment of inertia of the Earth?
Once you know whether the moment of inertia increases or decreases, you can determine from the equation whether the angular speed ω has to increase or decrease to keep L constant. How does the angular speed of Earth affect the length of the day?
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The Earth is rotating because it has angular momentum. When an event such as a bridge collapse occurs, the distribution of mass on Earth changes, but the total angular momentum is conserved.
Consider the equation L = I ω. The angular momentum L is conserved, but the moment of inertia I has changed. We know that moment of inertia is greatest when the mass is distributed closer to the axis of rotation.If an underwater bridge collapses and falls, does this increase or decrease the moment of inertia of the Earth?
Once you know whether the moment of inertia increases or decreases, you can determine from the equation whether the angular speed ω has to increase or decrease to keep L constant. How does the angular speed of Earth affect the length of the day?