forces.js

var particle;
var gravity;
var wind;

function setup() {
  createCanvas(800, 800);
  particle = new Particle();
}

function draw() {
  background(51);
  particle.update();
  particle.display();

  gravity = createVector(0, 0.1);
  particle.applyForce(gravity);

  particle.edges();

  wind = createVector(0.01, 0);
  if(mouseIsPressed) {
    particle.applyForce(wind);
  }
}

// Object below ///////////////////////////////////////////


function Particle() {
  this.pos = createVector(width/2, height/2);
  this.vel = createVector(0, 0);
  this.acc = createVector(0, 0);
  this.applyForce = function(force) {
    this.acc.add(force);
  }

  this.update = function() {
    this.vel.add(this.acc);
    this.pos.add(this.vel);
    this.acc.set(0, 0);
  }

  this.display = function() {
    fill(255);
    ellipse(this.pos.x, this.pos.y, 48, 48);
  }

  this.edges = function() {
    if (this.pos.y > height) {
      this.vel.y *= -1;
      this.pos.y = height;
    }
    if (this.pos.x > width) {
      this.vel.x *= -1;
      this.pos.x = width;
    }
  }
}