this.pos = createVector(x,y);

  this.prev = createVector(x,y);

  this.vel = createVector(1,0);

  this.acc = createVector(0,0);

  this.size = random(10,20);

  this.update = function() {

      this.vel.add(this.acc);

      this.vel.limit(5);

      this.pos.add(this.vel);

      this.acc.mult(0);

    }

  this.show = function(){

    stroke(0)

    fill(0)

    circle(this.pos.x,this.pos.y,this.size);

    this.prev.x = this.pos.x;

    this.prev.y = this.pos.y;

  }

}

​