private void loadPowerUpSprites() {
        // create "goal" sprite
        Animation anim = new Animation();
        anim.addFrame(loadImage("goal.png"), 150);
        goalSprite = new PowerUp.Goal(anim);

        // create "shield" sprite
        anim = new Animation();
        anim.addFrame(loadImage("shield1.png"), 100);
        anim.addFrame(loadImage("shield2.png"), 100);
        anim.addFrame(loadImage("shield3.png"), 100);
        anim.addFrame(loadImage("shield2.png"), 100);
        shieldSprite = new PowerUp.Shield(anim);
        
        // create stop sprite
        anim = new Animation();
        anim.addFrame(loadImage("stop.png"), 100);
        stopSprite = new PowerUp.Stop(anim);
        
        anim = new Animation();
        anim.addFrame(loadImage("oneUp1.png"), 100);
        anim.addFrame(loadImage("oneUp2.png"), 100);
        anim.addFrame(loadImage("oneUp3.png"), 100);
        anim.addFrame(loadImage("oneUp2.png"), 100);
        oneUpSprite = new PowerUp.OneUp(anim);
        
    }