The Earth is dynamic. Everything from windstorms to ocean waves is directly linked with the Earth’s constant motion’s predictable rhythms. Motion started back in the early days of the galaxy before the Earth had even formed. Geography is about appreciating “the big picture” to reveal geographic patterns and processes. It creates Earth’s environment 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 centre, forming the Sun. But a tiny fraction of a percentage spun out. That 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.
The Earth spins or rotates from the North Pole through the planet’s centre to the South Pole on an imaginary axis. It takes the Earth under 24 hours, or one day, to spin once on its axis. The Earth is spinning at about 1600 kilometres per hour at the equator. 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?
The rotation of the Earth, or its spinning motion, is a result of its initial angular momentum acquired during its formation. Here’s a more detailed explanation:
Conservation of Angular Momentum: When the solar system is formed from a rotating cloud of gas and dust, the system’s total angular momentum remains constant unless acted upon by an external torque. Angular momentum is a property related to an object’s mass, shape, and rotation. According to the law of conservation of angular momentum, an isolated system will maintain its total angular momentum.
Protosolar Nebula: The solar system originated from a large, rotating cloud of gas and dust known as the protosolar nebula. As the cloud collapsed under the influence of gravity, it began to spin faster due to the conservation of angular momentum. The central region of the collapsing cloud eventually formed the Sun, while the remaining material formed the protoplanetary disk.
Formation of Earth: Within the protoplanetary disk, smaller clumps of matter, called planetesimals, merged together through collisions and gravitational attraction. Over time, these planetesimals grew and eventually formed protoplanets, including Earth.
Angular Momentum Transfer: As planetesimals and protoplanets merged, their individual angular momenta combined and transferred to the growing Earth. The collisions and accretion of material caused the Earth to gain rotational motion.
Differentiation and Conservation: As Earth accumulated mass, its interior heated, leading to melting and differentiation. The denser materials sank toward the core, while lighter materials rose to form the Earth’s crust. During this process, the Earth’s overall angular momentum remained conserved.
Present-Day Rotation: Over billions of years, the Earth’s rotation has gradually slowed due to tidal interactions with the Moon, the redistribution of mass within the Earth, and the transfer of angular momentum to the Moon. Despite the slowing, Earth continues to rotate, and one complete rotation takes approximately 24 hours, resulting in the cycle of day and night.
Approximately 4.5 billion years ago, the solar system was formed in a hydrogen cloud, 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 different atoms 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 spun faster. This cloud of hydrogen formed the Sun in the centre, and the planets began to form in collide. This is why the Earth spins, and most 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 toward it, such as the tides.
The Earth has several layers made of a bunch of different substances. For inertia, all little parts are trying to move in straight lines.
- Newton’s first law says that anything will move steadily 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, a force must be preventing it. That’s where Newton’s second law tells us that an unbalanced force is causing acceleration. But its speed is steady: 1 rotation every 24 hours. Acceleration isn’t about a change in speed. It is a change in “velocity,” which involves direction too. Circular motion occurs if the force is never along the direction of motion.
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. Also, it’s caused by subatomic particle interactions, intermolecular forces, and gravity on the largest scale.
When describing 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 call that “rotational inertia.” We multiply by a distance and call that torque for any forces that change the speed. That still looks and works a lot like Newton’s second law.
The Earth isn’t wobbling around arbitrarily in space. Also, It travels on a 940 million-kilometre 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 the distance between the Earth and Sun varies throughout the year. Specifically, in January, the Earth is nearest the Sun or perihelion. The Earth is almost five million kilometres 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 kilometres per hour. It means you are travelling at something like 465 meters per second or less at the right moment. Everything inside is travelling at the same speed. Earth rotates on its axis every 23 hours & 56 minutes, spinning almost constantly. Nothing like a drag in space stops things from moving as they continue their journey through time.
Effects of Rotation of the Earth
Everything, including the atmosphere, rotates with us, so we don’t recognize that we’re spinning. If we were floating above the North Pole, Earth would rotate 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 receives light and solar energy from the other half 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 affected 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. The coefficients are the 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 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.
More Scientific Articles:
Dennis D. McCarthy; Kenneth P. Seidelmann. Time: From Earth Rotation to Atomic Physics.
Stephenson, F. Richard. “Historical eclipses and Earth’s rotation.” Astronomy & Geophysics.
Knapton, Sarah. “The Earth is spinning faster now than at any time in the past half century.”