31:T447,forceSim = { const au = height / 3; // Astronomical unit const gravity = 0.3; // Regulates mechanics speed const planet = { id: 'planet', mass: 10, x: 0, y: -au, vx: Math.sqrt(1000 * gravity / au), vy: 0 }; // vx set to orbital speed: sqrt(GM/d) const moon = { id: 'moon', mass: 0, x: 0, y: -au * 1.5, vx: 1.1 * Math.sqrt(10 * (gravity * 500) / (au * 0.5)), vy: 0 }; const bodies = [{ id: 'sun', mass: 1000, fx: 0, fy: 0 }, planet, moon], links = [ { source: 'planet', target: 'sun', attraction: gravity }, { source: 'moon', target: 'planet', attraction: gravity * 500 } // Higher attraction = more revolutions ]; const forceSim = d3.forceSimulation() .alphaDecay(0) .velocityDecay(0) .nodes(bodies) .force("gravitate-around", d3.forceMagnetic() .id(d => d.id) .charge(node => node.mass) .strength(link => link.attraction || 0.1) .links(links) ) .on('tick', () => { mutable planetPos = [planet.x, planet.y]; mutable moonPos = [moon.x, moon.y]; }); return forceSim; }32:[] 2f:{"title":"ForceMagnetic based Hierarchical Orbits","cells":[{"id":0,"value":"# ForceMagnetic based Hierarchical Orbits\n\nSimulation of multiple particles orbitting around each other in a hierarchical system (e.g. sun > planet > moon).\n\nUses D3's force plugin [forceMagnetic](https://github.com/vasturiano/d3-force-magnetic) to connect particles to their moving gravitational centers via magnetic/electrostatic links. These magnetic attraction forces simulate the mechanics of gravity. \nEach link holds its own gravitational constant to exaggerate the amplitude and velocity of the orbits relative to each other, which would be otherwise impossible in a system with a single constant.\n\nCompare with the [forceLink version](forcelink-based-hierarchical-orbits).","pinned":false,"hidden":false,"mode":"md"},{"id":10,"value":"\n${trailsCanvas}\n","pinned":false,"hidden":false,"mode":"html"},{"id":20,"value":"mutable planetPos = [0, 0]","pinned":false,"hidden":false,"mode":"ojs"},{"id":23,"value":"mutable moonPos = [0, 0]","pinned":false,"hidden":false,"mode":"ojs"},{"id":29,"value":"trailsCanvas = html``","pinned":false,"hidden":false,"mode":"ojs"},{"id":37,"value":"addTrailDot(planetPos)","pinned":false,"hidden":false,"mode":"ojs"},{"id":110,"value":"addTrailDot(moonPos)","pinned":false,"hidden":false,"mode":"ojs"},{"id":113,"value":"addTrailDot = pos => {\n d3.select(trailsCanvas).append('circle')\n .attr('id', 'trail')\n .attr('r', 1.5)\n .attr('cx', pos[0])\n .attr('cy', pos[1])\n .transition().duration(5000)\n .style('opacity', 0)\n .remove();\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":18,"value":"$31","pinned":false,"hidden":false,"mode":"ojs"},{"id":13,"value":"**Settings**","pinned":false,"hidden":false,"mode":"md"},{"id":15,"value":"height = 500","pinned":false,"hidden":false,"mode":"ojs"},{"id":5,"value":"**Dependencies**","pinned":false,"hidden":false,"mode":"md"},{"id":7,"value":"d3 = require('d3@7', 'd3-force-magnetic')","pinned":false,"hidden":false,"mode":"ojs"}],"files":"$W32","stdlib":"1","titling":"auto"}