Why Earth’s spin eases the pull
Gravity pulls you toward Earth’s center, but standing on a rotating planet adds another effect. In the planet’s rotating frame, you experience a small centrifugal effect—an apparent outward push caused by the ground and everything on it moving in a circle. At the equator, that circle is widest, so the effect is strongest; at the poles, it is essentially absent. The outward effect slightly reduces the force your feet press against the ground.
A bathroom scale senses that force, not your mass directly. With less force pressing on it, the scale reports a slightly lower weight even though the amount of matter in your body has not changed.
Earth’s shape adds to the difference
Earth is not a perfect sphere. Its rotation has made it bulge around the equator, so the surface there is farther from Earth’s center than the surface near the poles. Because gravity weakens with distance, that extra separation also makes the downward pull a little smaller.
These two effects work together: rotation reduces the effective pull most at the equator, and the equatorial bulge places you farther from the mass pulling you inward. The combined difference is about half a percent between the equator and the poles. It is small enough to escape notice in everyday life, but measurable with precise instruments—and it means the same person can register a slightly different weight simply by changing latitude.
