Does the Earth Rotate Slower or Faster at the Top?

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The Earth as a whole rotates 360 degrees once every 24 hours. This rotation is responsible for the appearance of the sun “rising” in the East and “setting” in the West. The surface speed of the Earth’s rotation at the top -- technically known as the geographic North Pole -- is slower than that of the vast majority of other places on the planet but equal to that of one other terrestrial location.

TL;DR (Too Long; Didn't Read)

The top (and bottom) of the earth travel slowest, while the earth rotates fastest in the center.

Earth’s Axis

To understand the reasons for differences in the Earth’s rotational speed, it helps to become familiar with the basic facts of rotation. The Earth rotates around an invisible line known as its axis, which extends from its top, the North Pole, through its center and to the bottom, or South Pole. For a visual representation of this, imagine a carousel spinning around its stationary support structure; this support structure is akin to the Earth’s axis. Essentially, the geographic North and South Poles are fixed endpoints at which the planet spins on.

Distance Differences

Because the Earth is a sphere, it is widest at the equator, becoming increasingly narrow further toward its top and bottom. This means that the Earth’s circumference, or distance around, is greatest at the equator, lessening with higher latitudes until it becomes nonexistent at the poles. An analogy to this is tying a string around a basketball: More string is needed if it’s being tied around the ball’s center than near the ball’s top, and it’s impossible to tie a string around the very top. Understanding this difference in distance is crucial to figuring out the rest of the puzzle.

Travel Time

Now imagine looking down on the Earth from outer space, pretending it’s possible to observe a person standing on the equator while the Earth rotates about its axis. This person would travel a very substantial distance in 24 hours, compared to a person standing at the top of the Earth, who wouldn’t travel at all. The latter person would stand in place as the planet spins below him. The speed of the person at the equator is fast because she covers more distance in the same time span, while the speed of the person at the North Pole is zero because he has no distance to cover. Similarly, the speed of someone standing at the bottom of the Earth, or the South Pole, would also be zero.

Mathematical Breakdown

So, the Earth rotates fastest at the equator, and slowest -- essentially, not at all -- at the top and bottom, with the rotation speed at the middle latitudes falling somewhere in between these two extremes. Breaking it down mathematically, the circumference of the Earth at the equator is roughly 40,000 kilometers (24,855 miles), and of course the time that it takes for the Earth to complete one rotation is 24 hours. Because speed equals distance divided by time, an object situated at the equator is moving at a rate of about 1,667 kilometers per hour (1,036 miles per hour). At a latitude of about 40 degrees north -- along which cities such as Philadelphia and Columbus, Ohio, lie -- the circumference of the Earth is about 30,600 kilometers (19,014 miles). When divided by 24 hours, this results in a rotational speed of 1,275 kilometers per hour (792 miles per hour). And at the North Pole, the distance around the Earth is zero, and zero divided by 24 hours results in a speed of zero.

References

About the Author

Based in western New York, Amy Harris began writing for Demand Media and Great Lakes Brewing News in 2010. Harris holds a Bachelor of Science in Mathematics from Penn State University; she taught high school math for several years and has also worked in the field of instructional design.

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