rotating ground

HTML

<div id="info">Drop!</div>
<script src="http://cdnjs.cloudflare.com/ajax/libs/three.js/r70/three.min.js"></script>
<script src="http://threejs.org/examples/js/controls/OrbitControls.js">
    
</script>

CSS

#info {
    position: absolute;
    top: 0px;
    width: 100%;
    padding: 10px;
    text-align: center;
    color: #ffff00
}
body {
    overflow: hidden;
}

JavaScript

var camera, scene, renderer, geometry, material, mesh, light, controls;
var ball, plane;
var clock = new THREE.Clock();

// class defintion here
var Ball = function () {
    
    // properties
    this.pos = new THREE.Vector3(0, 100, 0);
    this.vel = new THREE.Vector3();
    this.force = new THREE.Vector3(0, -50, 0);
    this.mesh = new THREE.Mesh(new THREE.SphereGeometry(5, 12, 12), new THREE.MeshBasicMaterial());
    scene.add(this.mesh);
    
    // methods
    this.update = function (dt) {
        this.vel.add(this.force.clone().multiplyScalar(dt));
        this.pos.add(this.vel.clone().multiplyScalar(dt));
        this.mesh.position.copy(this.pos);
    }
}

var Plane = function () {
    // properties
    this.pos = new THREE.Vector3(0, 10, 0); // object frame
    this.normal = new THREE.Vector3(0, 1, 0); // object frame
    this.mesh = new THREE.Mesh(new THREE.BoxGeometry(200, 20, 200), new THREE.MeshLambertMaterial());
    scene.add(this.mesh);
    
	// methods
    this.isPointOut = function (point) {

        // considering plane transformation
        var posW = this.pos.clone(); // in world frame
        var normalW = this.normal.clone();
        posW.applyMatrix4(this.mesh.matrixWorld);
        var tt = new THREE.Matrix4();
        normalW.applyMatrix4(tt.getInverse(this.mesh.matrixWorld).transpose());

        var tmp = new THREE.Vector3();
        tmp.subVectors(point, posW);
        if (tmp.dot(normalW) > 0) return true;
        else return false;
    }
};


init();
animate();

function ProjVonU(v, u) {
    var uhat = u.clone().normalize();
    return uhat.multiplyScalar(uhat.dot(v));
}

function CollisionResponse(ball, plane) {
    
    // considering plane transformation
    var posW = plane.pos.clone(); // plane in world frame
    var normalW = plane.normal.clone();
    posW.applyMatrix4(plane.mesh.matrixWorld);
    var tt = new THREE.Matrix4();
    normalW.applyMatrix4(tt.getInverse(plane.mesh.matrixWorld).transpose());


    // position...