[RadioAstronomer]

Hmmm... Then if I drill down 100 miles, then as far as the net gravitational pull on me goes, it would be like I was standing on a planet whose diameter was 200 miles smaller than Earth's? Because all the mass located farther out from the center than myself would be like that massive sphere in your example?

Think of it this way. G decreases at a linear rate as you approach the center of the Earth if it was a uniform density. (as the radius "r" decreases from the center)

Geek alert: Since the density is not uniform and much of the mass is contained near the center, G would initially increase.

[jennyp]

Geek alert: Since the density is not uniform and much of the mass is contained near the center, G would initially increase.

Huh. Now that's interesting!

[longshadow]

G decreases at a linear rate as you approach the center of the Earth if it was a uniform density.

Assume you meant "g" not "G."

The Gravitational constant "G" is constant.

The gravitation acceleration "g" varies with mass.....