We know that the acceleration due to gravity at the surface of the Earth is 9.8m/s2. We also know that the acceleration due to gravity falls off as 1/r2 above the surface of the Earth, with r being measured from the center of the planet.
There's one other domain, what's the value of gravity below the surface of the Earth? Sir Isaac Newton showed that the M term in gravity for the Earth can be set equal to the amount of mass contained inside a sphere of radius r centered upon the middle of the Earth in cases where we are investigating rEarth. Please find the value of g when we are 1/2 of the way from the center to surface of the Earth.