Gravitational field

Field first, force second. A mass sets up a gravitational field everywhere around it, and any second mass placed in that field feels a force. The AP Physics 1 CED defines the magnitude of the field created by a system of mass $M$ as the ratio of the gravitational force exerted by the system on a test object to the mass of that test object, giving the derived equation $g = F_g/m = GM/r^2$.

The units are the point of this entry. Field strength is force per unit mass, so it is measured in newtons per kilogram, and the AP Table of Information prints $g = 9.8\ \text{N/kg}$ alongside $g = 9.8\ \text{m/s}^2$. Same number, because a newton per kilogram and a meter per second squared are the same combination of base units. The CED joins them up: if the gravitational force is the only force exerted on an object, the observed acceleration in $\text{m/s}^2$ is numerically equal to the magnitude of the gravitational field strength in N/kg at that location.

The field is a vector pointing toward the mass that produces it, and it exists whether or not anything is there to feel it. Doubling the test mass doubles the force and leaves the field untouched.

One caution about the number itself. The Topic 2.6 essential knowledge gives the field strength near Earth's surface as about 10 N/kg while the equation table prints 9.8. Both are real, and is g 9.8 or 10 sorts out which to use.