net force on each body
force pairs on the selected body
Drop masses on the sheet. Heavier objects dig deeper wells, and everything rolls toward everything else.
What the fabric shows. Motion is computed with Newton's law, F = G·m₁·m₂ / r², in simulation units (G = 1). The dent at each point is drawn from the gravitational potential there, so deep wells mean strong pull. The rubber-sheet picture is an analogy: a real sheet sags because Earth's gravity pulls it down, and general relativity curves time as well as space. Arrow length grows with the square root of force so small and large forces both stay visible.