The claim that we weigh less at the equator because of centrifugal force is not supported by empirical data. Natural variations of the gravitational field owing to variations in planet density are sufficient to account for the differences in weight. The equatorial bulge is sufficient to account for differences in weight across latitude. The results are consistent with the idea of the Earth creating its own spinning frame of reference relative to which, the planet itself is actually stationary.
The data
I asked an AI engine to give me the values of gravitational acceleration across the globe.
So the variation between poles and equator is the difference between 9.832 and 9.780 which is 0.052 m/s².
I now asked for typical variations across a single latitude
So the difference in gravitational strength between the poles and equator is less than that for the planet as a whole and is equal to the variation across a single latitude. This variation then may not be attributed to a spinning Earth without further evidence.
Equatorial bulge
I now asked the engine to summarise the variation in gravitational field strength according to the bulge of the equator alone.
So to get from the stronger gravity at the poles to the weaker gravity at the equator we take the pole value of 9.832 and multiply by 0.9933 to get the value of 9.766. The difference between these two values is 9.832 minus 9.766 which is 0.066 m/s², that is to say, an even bigger difference than actually measured. There is no need for any additional adjustment to be made here; everything is explained by bulge alone.
Too many variables?
We have a measured variation of 0.05 – 0.07 m/s², across the globe, along lines of latitude and from equator to pole. W have theoretical variations of 0.05 predicted from crustal variations, centrifugal forces and equatorial bulge.
Sometimes a measurement is attributed to crustal variation, sometimes to equatorial bulge and sometimes to centrifugal force, seemingly dependent upon the argument to be made at the time.
This is no way to do science. There are too many variables to be resolved in a few ad hoc experiments and certainly, in the data above, no chance of sensibly interpreting any single measurement or attributing any single cause with any degree of certainty.
Centrifugal force?
The variations in weight at the poles and equator is adequately explained by the bulge of the planet at the equator. There is no need to bring centrifugal force into the equation as there is simply no requirement for it given the data.
If the calculations and measurements above are correct then additional adjustments for centrifugal force will in fact give incorrect results. This suggests that centrifugal forces at the planetary scale are not merely irrelevant but perhaps even non-existent.
A rotating frame of reference
Experiments demonstrating the existence of centrifugal force are all small scale affairs and performed in laboratories within the Earth’s magnetic field, whether at the surface of the Earth or in freefall nearby. The effects seen can therefore be explained by the action of objects moving through an ‘inertial field’ as explained here: Gravity as an inertial field
It is far from obvious, however, that the phenomena of rotation, Coriolis forces and centrifugal forces can simply be transferred from a laboratory to the scale of a planet within a solar system. If scientists claim that they can, then this must be rigorously demonstrated with data and arguments that are somewhat more reliable than the ones presented above.
Attempts to demonstrate the rotation of the Earth by means of a Foucault pendulum are no more rigorous and no more conclusive than those described above: Gravity as an inertial field
If the Earth’s inertial field rotates along with its mass, then there is no centrifugal force to alter the weight of an object at the equator. This is entirely consistent with the above data and even supported by it.