function ContactMaterial(m1, m2, options){
    options = Utils.defaults(options, {
        friction: 0.3,
        restitution: 0.3,
        contactEquationStiffness: 1e7,
        contactEquationRelaxation: 3,
        frictionEquationStiffness: 1e7,
        frictionEquationRelaxation: 3
    });

    /**
     * Identifier of this material
     * @property {Number} id
     */
    this.id = ContactMaterial.idCounter++;

    /**
     * Participating materials
     * @property {Array} materials
     * @todo  Should be .materialA and .materialB instead
     */
    this.materials = [m1, m2];

    /**
     * Friction coefficient
     * @property {Number} friction
     */
    this.friction = options.friction;

    /**
     * Restitution coefficient
     * @property {Number} restitution
     */
    this.restitution = options.restitution;

    /**
     * Stiffness of the produced contact equations
     * @property {Number} contactEquationStiffness
     */
    this.contactEquationStiffness = options.contactEquationStiffness;

    /**
     * Relaxation time of the produced contact equations
     * @property {Number} contactEquationRelaxation
     */
    this.contactEquationRelaxation = options.contactEquationRelaxation;

    /**
     * Stiffness of the produced friction equations
     * @property {Number} frictionEquationStiffness
     */
    this.frictionEquationStiffness = options.frictionEquationStiffness;

    /**
     * Relaxation time of the produced friction equations
     * @property {Number} frictionEquationRelaxation
     */
    this.frictionEquationRelaxation = options.frictionEquationRelaxation;
}
Defines what happens when two materials meet.
@class ContactMaterial
@constructor
@param {Material} m1
@param {Material} m2
@param {object} [options]
@param {Number} [options.friction=0.3]
@param {Number} [options.restitution=0.3]
@param {number} [options.contactEquationStiffness=1e7]
@param {number} [options.contactEquationRelaxation=3]
@param {number} [options.frictionEquationStiffness=1e7]
@param {Number} [options.frictionEquationRelaxation=3]