The Earth spins 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 the poles is slower than the surface speed of rotation at the equator. This seemingly funky phenomenon can be explained through the physics of rotating objects, and it has many surprising implications on Earth’s surface conditions.
TL;DR (Too Long; Didn't Read)
The top (and bottom) of the earth travel slowest, while the earth rotates fastest around the equator.
To understand the reasons for differences in the Earth’s rotational speed, it helps to become familiar with the basic facts of rotation. The planet 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.
As you move further from the equator, this geometry and the rotation of Earth results in longer and shorter days during different times of the year. The length of a day and night actually stretch months at a time, as you get to the north and south poles. It’s important to note that Earth’s days do not technically change in duration (they are still 24 hours), but the time of daylight varies. This is similar to the ‘shortest day’ being the winter solstice, but the length of the day is still technically 24 hours.
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.
Now imagine looking down on the Earth from the moon (around 240,000 miles away in Earth’s orbit), and think of observing 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 they covers more distance in the same time span, while the speed of the person at the North Pole is zero because they have no distance to cover. Similarly, the speed of someone standing at the bottom of the Earth, or the South Pole, would also be zero.
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 New York 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.
Even the slower speeds in Philadelphia or New York are still blazing fast. You would still be moving over 1000 feet per second, or over 1 foot per millisecond while just sitting still.
The rotation of the Earth and all of the stuff on Earth’s surface interact in very interesting patterns and models.
The variation in speed of Earth’s rotation causes an atmospheric effect called the Coriolis Force. As atmosphere gets closer to the equator, it experiences a sense of speeding up, or increased velocity, because the surface beneath it moves more quickly. This results in variation between atmospheric speeds in the upper parts of the northern hemisphere, the equator, and the lower parts of the southern hemisphere. These atmospheric differentials are very important when understanding the implications of long term patterns in the atmosphere, especially with the continued challenges of climate change, wildfires, and pollution.
While the Coriolis effect describes an impact of the Earth’s rotation on the atmosphere, there is actually potential influence on the Earth’s own axis of rotation that comes from oceanic and atmospheric change. A phenomenon called the Chandler Wobble describes a deviation from the standard access of rotation. Theoretically, this deviation should experience a slowdown effect over significant timescales. For many years, the cause of this continued deviation was uncertain, but then scientists at JPL (a division of NASA) found through interactive simulations of the Earth, that large-scale turbulence in the oceans and atmosphere (caused by the wobble and the rotation) actually contribute back to the wobble over time.
The rotation of the Earth is also thought to contribute to the Earth’s magnetic field. The rotation of the Earth’s magnetic mantle and core beneath the surface is influenced, but not identical, to the outward rotation of the Earth.
Throughout the solar system, many celestial bodies experience very different patterns of rotation and the effects thereof. Venus rotates in the opposite direction, while Uranus rotates with an extremely skewed axis of rotation.
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.