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Strictly speaking, $g$ (even more strictly speaking, $g_0$ or $g_n$) is a constant. It is exactly 9.80665 m/s$^2$, by definition. There are many places in science and engineering where it is very useful to have an exact (albeit arbitrary) defined constant for gravitation on the surface of the Earth. That said, gravitation on the surface of the Earth does ...

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To two significant figures, the acceleration due to gravity is $g=9.8\:\mathrm{m/s^2}$ everywhere on Earth (at sea level). That is to say, if you use e.g. a pendulum to measure $g$ to two sig figs, you will get this value no matter where you are. In a sense, this is the precision to which the Earth is well-approximated by a uniform sphere of matter. The ...

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You ask a lot of questions, I'll try to answer just one. As the Earth's magnetic field protects us from ionizing radiation, theoretically, there can be negative correlation between the Earth's magnetic field and cancer incidence. EDIT: see, e.g., Health Physics; v. 34(3) p. 237-247; ISSN 0017-9078; 1978 ...

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Yes, the strength of the Earth's gravity changes (slightly) from place to place. However, you can't just treat Earth's gravity as a varying number; it is a vector. It mostly points down towards the center of the Earth, but those same gravitational anomalies which cause the general strength of gravity to vary also cause it to deviate from what you'd generally ...

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I think that the problem here is that $U = mgh$ is an approximation that we can make by assuming a constant value of $g$. Even taking it a bit further and using $$U = -G\frac{m_1m_2}{r}$$ will make some assumptions about the density and shape of earth if you consider one of the masses to be that of the whole earth. In reality, you'd need to sum the ...

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Let's do some rough estimation. Considering: CuriousOne's very good and fitting comment with regards to geometrical estimation given in question and the last but not least the human physiology ($10^{-12} \ W$ can hear only a full healthy man, with perception much less than a whisper and only on a frequency range improbable due to the diffraction) we ...

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