Spatial Forces
Directional relationships between elements that guide the eye and imply connection or tension across a composition.
In practice
Spatial forces are the pulls and tensions the eye senses between elements. Two shapes placed close together seem attracted, a shape near an edge seems to press against it, and a pointing form leads the eye in its direction. Designers use these forces to link content without drawing lines. On a poster, a photo of someone looking to the right pushes attention toward a headline placed on that side.
Often confused with Dynamics
Dynamics is movement implied within forms; spatial forces are the attractions and tensions between separate elements that carry the eye from one to another.
Try this
Place two small circles on a page, move them closer and farther apart, and note when they stop feeling connected.