The acceleration of free-falling objects on Earth varies. It depends on various factors. The figure of 9.8 m/s² is just a nominal value to use if the actual local value is unknown or unimportant. These variations can only be explained using the law of gravity and that the Earth is a rotating sphere.
Flat-Earthers claim that science tells us that Earth’s gravitational acceleration is always 9.8 m/s² everywhere on Earth, and they use it as “evidence” Earth is flat and stationary. But, in reality, Earth’s gravitational acceleration does indeed vary in different locations.
The value of 9.8 m/s² is only an approximation. It is very close to the actual value everywhere on Earth, and close enough for most practical applications. The real value does differ by about 0.5%. An object at the poles will weight approximately 0.5% more than at the Equator.
The various factors that determine the magnitude of Earth’s gravity:
- Latitude. The equator is farther away from the center of the Earth than the poles. The equator is also getting the highest centrifugal acceleration due to Earth’s rotation.
- Altitude. Greater altitude means greater distance from Earth’s center of gravity, and therefore causes a weaker gravity.
- Depth. If we go deeper below Earth’s surface, gravity becomes weaker because the mass above us will pull us upward instead of down.
- Local topography & geology. Denser rocks under the ground below us will cause a stronger gravity.
Taking a scale to another location will no longer result in the correct measurement and will require recalibration. These gravity variations can only adequately be explained using the law of gravity and that Earth is a rotating sphere.