Force Layout - Charge

All the Nodes are assigned with Negative charges.

All but the bigger Node have same negative charge. The Bigger node has a bigger negative charge and so it repels more.

Try to drag the bigger node nearer to other nodes

<html>
    <head>
        <title>D3 Force Layout Charge Example</title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <link rel="stylesheet" href="main.css">
        <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
    </head>
    <body>
        <script>
            var w = 800;
            var h = 450;
            var margin = {
                top: 20,
                bottom: 20,
                left: 20,
                right: 20
            };
            var width = w - margin.left - margin.right;
            var height = h - margin.top - margin.bottom;

var svg = d3.select("body")
                    .append("svg")
                    .attr("id", "chart")
                    .attr("height", h)
                    .attr("width", w);

var colorScale = d3.scale.category20();

var nodes = [15, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10].map(function (d) {
                return {"radius": d};
            });

var force = d3.layout.force()
                    .nodes(nodes)
                    .size([w, h])
                    .charge(function (d, i) {
                        return (i == 0) ? -1000 : -100;
                    })
                    .on("tick", tick)
                    .start();

var circles = svg.selectAll("circle")
                    .data(nodes)
                    .enter()
                    .append("circle")
                    .attr("r", function (d) {
                        return d.radius;
                    })
                    .style("fill", function (d, i) {
                        return colorScale(i);
                    })
                    .call(force.drag);

Modified http://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js to a secure url

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js