Why is the earth constantly rotating, but we as humans can never feel it?

[D H]

Can it be said that, regardless of your latitude, be it 0, 45 or 90, your weight will be constant as long as you are at seal level? i.e. that is the point where any non-spherical and rotational forces balance out.

You are still confusing weight (i.e., force) and energy. Mean sea level is an equipotential surface, not a equal weight (equal force) surface. As mentioned above, force is the gradient of the potential field. Your weight would be constant if and only if the geopotential had spherical symmetry (which it does not have).

 

[DaveC426913]

No, your mass is constant, not your weight. Think of your weight at the moon.

I am well aware of this fact. I'm pretty good with the physics.

I am suggesting that it is indeed your weight that is constant anywhere at sea level.


Actually, this has cause and effect reversed. One can define a geoid near the Earth's surface where the gravitational force from the oblate spheroid and the (centrifugal) inertial rotational force balance out, making for a constant net force. This is true (since you're defining it).

My suggestion is that, if there's water in the oceans above this geoid, and elsewhere, water below this geoid, the water will behave as if flowing "downhill" until it is everywhere (weather/pressure effects aside) at the same level, mirroring the geoid. Thus, sea level will ultimately reflect a surface where vertical forces balance. This being the case, one can stand at sea level anywhere in the world and expect one's weight to be the same.


This is my intuition. I can't back it up with facts or figures, so I'm going to have to concede the point to those who are able to demoinstrate otherwise.

 

[billiards]

I thought we agreed that the geoid was an equipotential surface and that it was not a perfect sphere?

Now all you need to do is say "okay I've got the same amount of potential energy anywhere on the geoid" (which I hope you see follows naturally). But the geoid at the poles is closer to the Earth's centre of mass than the geoid at the equator, and clearly the point that is the centre of mass is where your gravitational potential is zero.

That means that the rate of change of the potential is greater at the poles than at the equator, right?

Effectively this means that g is also greater at the poles, thus you weigh more there but still have the same amount of gravitational potential energy as you do anywhere else on the geoid.