An optical trap pulls the bead back toward center with a force equal to stiffness times displacement, so the restoring arrow always points opposite the displacement. With stiffness 2 N/m and displacement 3 m, the force magnitude is 2 times 3 = 6 N exactly for the stated toy force ledger; real traps need stiffness calibration, drag and thermal noise handling, bead-size effects, alignment, and measurement uncertainty.
A calibrated trap produces a restoring force with checked magnitude. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Trap stiffness turns displacement into force
Use stiffness 2 newtons per metre with displacement 3 metres.
2⋅3
The restoring force points back
The force magnitude is 6 newtons, and the arrow points back toward the trap center.