To answer the question of how fast Earth spins, you need to know two things: how long it takes to make a full rotation, and Earth’s circumference. The time it takes Earth to rotate so the sun appears in the same position in the sky, known as a solar day, is 24 hours. However, the time it takes Earth to complete one full rotation on its axis with respect to distant stars is actually 23 hours 56 minutes 4.091 seconds, known as a sidereal day.
With this information, to work out how fast Earth is spinning we need only our planet’s circumference. At the equator, its circumference is roughly 40,075 kilometres, so dividing this by the length of day means that, at the equator, Earth spins at about 1670 kilometres per hour.
However, this speed of rotation isn’t consistent across the planet. As you move north or south, the circumference of Earth gets smaller, so the speed of spin reduces until it reaches its slowest at both poles. And all of this is nothing compared with the 107,000 kilometres per hour at which Earth orbits the sun.
If we are travelling so fast through space, why can’t we feel it?
Simply put, as Earth is spinning at a constant speed, so does everything on it. Travelling at the same speed means we cannot feel the spin. It is like driving a car. Even though you are moving, you aren’t aware of speed because it is constant. Only when you change speeds do you notice you are travelling, like putting your foot on the accelerator or making an emergency stop.
A change in speed has been happening here on Earth, but it is far too slow to notice. Millions of years ago, one Earth day was about 22 hours, and Earth’s speed has been dropping for more than a billion years, with days increasing by around 2 milliseconds every century.
This slow down is caused by friction created by the ocean currents, tides and wind pulling on Earth’s surface. However, global warming may speed things up again. As sea level rises, this change in mass could result in Earth spinning faster and reducing the length of each day by 0.12 milliseconds, which would have dramatic effects on the calibration of atomic clocks and GPS systems.
What if Earth were to stop spinning?
Without a huge external force, this is impossible. But, if Earth were to stop spinning, the atmosphere would continue to spin at the speed of Earth’s rotation, so anything not fixed to the surface, including trees and buildings, would be swept away by the strong winds.
Each side of the planet would get six months of continuous sunlight and six months of darkness. Without the centrifugal force of the spin, the oceans would gradually move towards the poles, creating a huge supercontinent across the equator.
But we wouldn’t be flung off Earth. Gravity and the centrifugal force of Earth’s spin keep us grounded. In order for us to feel weightless, the centrifugal force would need to be ramped up. At the equator, Earth would need to spin at 28,437 kilometres per hour for us to be lifted off into space.
Read more at New Scientist