public void keyReleased(KeyEvent event) {
            switch (event.getKeyCode()) {
            case KeyEvent.VK_W:
                up = false;
                break;
            case KeyEvent.VK_S:
                down = false;
                break;
            case KeyEvent.VK_A:
                left = false;
                break;
            case KeyEvent.VK_D:
                right = false;
                break;
            default:
                // ignore other characters
            }
            //add actual forces
            updateForces();
        }