The Earth is dynamic. Everything from windstorms to ocean waves is directly linked with the Earth’s constant motion’s predictable rhythms. Motion turns out that started back in the early days of the galaxy before the Earth had even formed. Geography is all about appreciating “the big picture” to reveal the geographic patterns and processes. It creates Earth’s environments and supports all living things. About 13.7 billion years ago, the universe began.
About 4.5 billion years ago, a swirling cloud of gas and dust, called a solar nebula, collapsed under its gravity. It spun faster and faster and flattened into a disk. Almost all of the nebula’s material was sucked into the center, forming the Sun. But a tiny fraction of a percentage spun out. And that’s what formed the rest of the Solar System, including the Earth. We can still see the effects of this dramatic event in how the Earth and the rest of the planets and asteroids move throughout our solar system.
On an imaginary axis, the Earth spins or rotates from the North Pole through the center of the planet to the South Pole. It takes the Earth just under 24 hours, or one day, to spin once on its axis. At the equator, the Earth is spinning at about 1600 kilometers per hour. The rotation of the Earth at the equator is still 13 times faster than the top speeds of a cheetah.
Why does the earth rotate?
Approximately 4.5 billion years ago, the solar system was formed in a hydrogen cloud, much like the Eagle Nebula. This nebula started collapsing, most likely due to an external force such as a supernova the individual atoms began to run into each other. Due to this stronger gravity, each atom had a small amount of force, and they had different atoms that had to average out. It would be tough to average out perfectly even. So the cloud started to spin in a direction.
As the cloud of hydrogen kept getting smaller, it started to spin faster. This cloud of hydrogen formed the Sun in the center, and the planets began to form in collide. This is why the earth spins and why most of the other planets spin in the same direction. The earth is slowing down. The moon is gradually moving away from Earth, slowing it down. It is pulling things on earth, such as the tides toward it.
The Earth has several layers made of a bunch of different substances. For inertia, all of the little parts are trying to move in straight lines.
- Newton’s first law says that anything will move at a steady speed in a straight line until there’s a total or unbalanced force from the outside.
If the parts of the Earth aren’t doing this, there must be a force preventing it. That’s where Newton’s second law tells us that unbalanced force is causing an acceleration. But its speed is steady: 1 rotation every 24 hours. Acceleration isn’t just about a change in speed. It is a change in “velocity,” which involves direction too. If the force is never along the direction of motion, then circular motion occurs.
The speed never goes up or down. The force only changes the direction. The same thing is happening to the parts of the Earth while it spins. But it’s still an acceleration. And it’s caused by subatomic particle interactions, intermolecular forces, and, on the largest scale, gravity.
If you’re trying to describe a ball or the Earth’s motion, you don’t always want to consider its parts’ momentum and energy. So we ignore all the forces that only change direction and just call that “rotational inertia.” Any forces that change the speed, we multiply by a distance and call that a torque. That still looks and works a lot like Newton’s second law.
The Earth isn’t just wobbling around arbitrarily in space. Also, It travels on a 940 million kilometer path around the Sun, called an orbit. One complete orbit is a revolution, which takes 365 and a quarter days. Earth’s orbit is elliptical, like a slightly stretched-out circle. This means that the distance between the Earth and Sun varies a bit throughout the year. Specifically, the Earth is nearest the Sun, or at perihelion, in January. And the Earth is almost five million kilometers farther away from the Sun at aphelion, in early July.
Why can’t we feel the earth’s rotation? The speed of rotation of Earth is about 1675 kilometers per hour. It means at the right moment, you are traveling at something like 465 meters per second or less. Everything inside is traveling at the same speed. Earth rotates on its axis every 23 hours & 56 minutes, spinning almost at a constant rate. There is nothing like a drag in space to stop things from their motion as they keep going on their journey through time.
Effects of rotation of the Earth
Everything, including the atmosphere, rotates with us, which is why we don’t recognize that we’re spinning. If we were floating above the North Pole, Earth would be rotating counterclockwise. That gives the impression of the Sun rising in the east, moving across the sky as it climbs, and then setting in the west.
Half of Earth that’s currently receiving light and solar energy from the other half that’s in darkness. The Earth doesn’t spin ideally. It wobbles ever so slightly. Some of the Earth’s wobbling is predictable. Like a spinning top slowing down, the Earth’s axis wobbles on a 26,000-year cycle known as precession. It changes how the Earth’s hemispheres are oriented towards the Sun. So the star almost directly above the North Pole cycles through several stars over time.
Precession is one of the Milankovitch cycles named after the mathematician who deduced them in the 1940s. Milankovitch cycles influence Earth’s climate by changing how much solar energy reaches the Earth. But in 2000, the wobble took an unexpected and relatively “rapid” turn east. So with the help of the GRACE satellites launched by NASA and the German Aerospace Center to record data on anomalies in Earth’s gravity field, scientists looked for answers in the Earth’s mass.
They found that melting ice from Antarctica and Greenland is causing sea-level rise. It affects landmasses, too, pushing and pulling the Earth as it rotates. But human water use in Eurasia is affecting too! Groundwater beneath the surface is being used faster than the hydrosphere can naturally replace it worldwide. But as we get closer to 45 degrees north or south latitude, small changes have a big impact.
Coefficients in the equations that best describe the Earth’s wobbling depend on latitude. And the coefficients are biggest near 45 degrees north or south latitude. So any changes in mass that happen around there are amplified. NASA estimates dry years cause the Earth to wobble east, while in wet years, Earth wobbles west.
Over thousands of years, the eccentricity of the Earth’s orbit varies. As a result of gravitational attractions among the planets, primarily Jupiter and Saturn. The orbital eccentricity cycles with a period of roughly 100,000 years. As the eccentricity of the orbit involves, the semi-major axis of the orbital ellipse remains unchanged. So the length of the sidereal year remains unchanged. As the earth travels in its orbit, the duration of seasons depends on the orbit’s eccentricity.
When the orbital eccentricity is extreme, the seasons that occur on the orbit’s far side are substantially longer in duration. In addition to axial precession, there’s the axial tilt. A year on earth is directly determined by all the various orbital motions of the earth.
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