Gravity

[Frank]

I have not been able to find any threads covering my question in the FAQ department.

I presume gravity is strongest at the surface of the earth. What is the effect of gravity as you approach the center of the earth? (Presuming you could measure it deep below the surface) Does it become stronger or weaker?

[apodman]

Weaker.

Newton showed that if a mass object is located inside a spherical mass distribution then the gravitational force is only due to the mass in a sphere closer to the center than that of a small mass inside the sphere. For example, if you dug a deep hole, then the gravity acting on a small mass at the bottom of the hole would only be due to the mass of the Earth below the bottom of the hole. The gravitational force of the mass of the Earth above the bottom of the hole cancels out, i.e. its net vector sum adds up to zero.

[Chris Peterson]

I presume gravity is strongest at the surface of the earth. What is the effect of gravity as you approach the center of the earth? (Presuming you could measure it deep below the surface) Does it become stronger or weaker?

If the Earth were a sphere of uniform density, the acceleration from gravity would become weaker as you get closer to the center. At the very center, you would feel no gravitational force (from the Earth) at all. However, the Earth isn't uniform, but has a core with much higher density. The actual field is complex, but to a first approximation, the force stays fairly close to its surface value as you descend, increasing slightly to a maximum when you are about 3000 km deep, then dropping steadily to zero at the center.