So, for ordinary calculations, especially for less pressing interests in example problems and the like, 9.8 m/s² can be used because by looking at the difference between the gravity of the equatorial and polar regions which is not too significant and can still be rounded up to the nearest tenth.
Introduction:
Before we talk about the gravity acceleration that can change according to its location on the surface of the Earth. Its caused by the shape of the Earth's surface which is not perfectly spherical like we imagine. Generally, parts of the Earth have a different thickness (from the center of the Earth) between the equator and the poles, so there will also be differences in the acceleration of gravity between the poles and the equator. Because the thickness of the center of the Earth decreases, the more conical the latitude (towards the poles), the higher the acceleration due to gravity. However, this is not very significant. As a comparison, at the equator, the acceleration due to gravity will be around 9.76 m/s² while at the poles it is about 9.83 m/s².
The Answer:
The physical value of "g" in physics calculations is equivalent to 9.8 m/s², because the g value between the equator and the g value at the poles, can each be rounded to the nearest tenth. For example, we take the acceleration due to gravity at the equator, which is 9.76 m/s²s, since the hundredths digit is over 5, 9.76 m/s² can be rounded up to 9.8 m/s². The opposite occurs for the acceleration due to gravity in the polar regions, which is 9.83 m/s² which is rounded down because the hundredths digit is less than 5 (see the underlined number).
Conclusion:
So, for ordinary calculations, especially for less pressing interests in sample problems and the like, 9.8 m/s² can be used because taking into account the differences in gravity between the equator and the poles which are not too significant and can still be rounded up to the nearest tenth.