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 This module implements a [velocity Verlet](https://en.wikipedia.org/wiki/Verlet_integration) numerical integrator for simulating physical forces on particles. The simulation is simplified: it assumes a constant unit time step Δ*t* = 1 for each step, and a constant unit mass *m* = 1 for all particles. As a result, a force *F* acting on a particle is equivalent to a constant acceleration *a* over the time interval Δ*t*, and can be simulated simply by adding to the particle’s velocity, which is then added to the particle’s position.
 
-In the domain of information visualization, physical simulations are useful for studying [networks](https://observablehq.com/@d3/force-directed-graph) and [hierarchies](https://observablehq.com/@d3/force-directed-tree)!
+In the domain of information visualization, physical simulations are useful for studying [networks](https://observablehq.com/@d3/force-directed-graph/2) and [hierarchies](https://observablehq.com/@d3/force-directed-tree)!
 
 [<img alt="Force-Directed Graph" src="https://raw.githubusercontent.com/d3/d3-force/master/img/graph.png" width="420" height="219">](https://observablehq.com/@d3/force-directed-graph)[<img alt="Force-Directed Tree" src="https://raw.githubusercontent.com/d3/d3-force/master/img/tree.png" width="420" height="219">](https://observablehq.com/@d3/force-directed-tree)