Specific force is defined as the non-gravitational force per unit mass.

The primary non-gravitational force acting on satellites in low Earth orbit is atmospheric drag.

A non-gravitational force acting on the body, for example force arising from:

A concrete choice could be the four-momentum of a test body acted on by gravitational and non-gravitational forces.

The Yarkovsky effect is a small non-gravitational force on rotating bodies that can affect their trajectories.

The weak EP assumes falling bodies are bound by non-gravitational forces only.

Importantly, the world line of a particle free from all external, non-gravitational force, is a particular type of geodesic.

Bodies smaller than a few kilometers are dominated by non-gravitational forces and tend to be angular in shape.

However, the larger the body the less important become its non-gravitational forces in comparison with its internal gravitational forces.

This is because the gravitational forces are appreciable over much larger distances than the non-gravitational forces.