What would happen to Earth’s day if polar ice caps melted?
Topic Covered: rotational inertia
Have you ever wondered what’s going to happen if the polar ice caps of the Earth melted? Besides global warming, rise of sea levels, and release of greenhouse gases, the melting of the ice caps will also affect the day and night of the Earth.
But how? In order to figure that out, we need to know about the rotational inertia.
Inertia is resistance to acceleration. Objects with greater inertia are more likely to stay in their current motion. In other words, an object at rest wants to stay at rest and an object in motion wants to stay in motion. Rotational inertia is a resistance to rotational acceleration. An object with greater rotational inertia would not want to change its motion; it either wants to stay at rest, or stay at rotation.
In physics, rotational inertia, also known as the moment of inertia, is determined by the equation: I = MR2.* As you can see from the equation, I (rotational inertia) is proportional to M (mass) and R (radius, or distance from the axis of rotation). As the rotating object increases its mass and gets farther away from its axis of rotation, the rotational inertia will increase, making the object harder to rotate.
Think of it this way: pretend you have a rod with two masses attached to it, and you are rotating that rod by from the center. It would be much easier to rotate the rod if the masses are closer to the center than if the masses are farther away. Why? Because the greater the distance (R) from the axis of rotation, the greater moment of inertia the object will have!
Now let’s go back to our original question. What would happen to Earth’s day if polar ice caps melted? If the Earth warms significantly and polar ice caps melt, the water will move away from the poles (which is Earth’s rotation axis) and spread out around the globe, getting farther from the axis of rotation. If the radius (R) increases, the rotational inertia will increase, which would make Earth spin slower... Then we would have a longer day!
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* Rotational inertia for specific objects differ based on their shape. For example, the equation for rotational inertia of a sphere is I = 2/5MR2 and a disk is I = 1/2MR2. However, we’ll just use the equation I = MR2 because with the purpose of this post, we are more interested in knowing the relationship between variables rather than performing actual calculation.
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