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Why aren't we thrown off the Earth?
Gravity always prevails
Everything on Earth is pulled toward the center of the planet by gravity. Although Earth's rotation creates an outward centrifugal force, this force is very small compared to gravity.
Right at the equator, where the rotational speed is highest, centrifugal force only reduces our weight by about 0,3%. This figure is too small to cause humans or any object to be flung off the surface of the planet.
We are moving with the Earth
Not only the ground but also the atmosphere, oceans, and every object on Earth rotate along with the planet. We have been moving at this speed since birth, so we do not feel it.
The same thing happens when sitting on a plane flying steadily. Even though an airplane can reach speeds of hundreds of km/h, passengers inside still feel almost stationary as long as there are no vibrations or sudden changes in speed.
The body only senses changes in velocity
The nervous system and the vestibular system in the inner ear primarily sense acceleration, which is the change in speed or direction of motion.
Earth rotates very steadily, with almost no sudden changes that the body can recognize. Therefore, we do not feel ourselves hurtling through space even though we are actually moving with the Earth.
What would happen if Earth rotated twice as fast?
If one day Earth completed a rotation in just 12 hours instead of 24 hours, the world would change significantly.
Body weight decreases
When the rotational speed doubles, the centrifugal force increases approximately fourfold.
At the equator, this force would counteract about 1,2% of gravity.
Further reading
Syced / Wikimedia Commons — CC0
