this post was submitted on 19 Nov 2024
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Not quite. When you're rotating, you are constantly accelerating in a tangent direction to the diameter. So the poster is right that we should be feeling a force shooting us away from the center of earth.
Except the force of gravity cancels out the centripetal force and then some.
So [force of gravity] - [centripetal force of Earth's rotation] = 9.8m/s^2
The difference is about 0.5%. A mass weighing 100kg at the north pole would only weigh 99.5kg at the equator. Most of the difference is the centerfugal force of the earth's rotation.
I've not checked the numbers, but apparently it's detectable in Olympic sports. More height records get broken at equatorial latitudes that higher ones.
That assumes a perfectly spherical earth. The earth is not perfectly spherical.
This. Planets are in hydrostatic equilibrium, meaning that the combined acceleration by gravity and the centrifugal "force" is equal all over the world (except for local differences due to mountains and dense crust).
Hydrostatic equilibrium yes, but equal? No. We agree that centrifugal force is a factor. Now ask yourself, why would gravity suddenly strengthen at the equator to get the surface acceleration to stay equal to that of the poles?
It doesn't. As a result the Earth seeks a new hydrostatic equilibrium, bulging out at the equator. This in turn strengthens the centrifugal force a bit while also slightly diminishing the force of gravity (because more of the planet's mass is farther away). So the same effect is taken even further. Local differences add a layer of noise on top of this, but the end result is that the net surface acceleration is measured to average slightly less at equatorial regions than at the poles, with for example Singapore getting 9.7639 m/s2 of downward acceleration, while Helsinki gets 9.825 m/s2.
You're right, I had it backwards. Hydrostatic equilibrium makes it that the combined force vector of gravity and the centrifugal force is perpendicular to the planet surface everywhere.