- (void) initializeTimerWithNSTimer
{
    CGFloat interval = 1.0f / 50.0f;
    [NSTimer scheduledTimerWithTimeInterval:interval
                                     target:self
                                   selector:@selector(animateBallNSTimer:)
                                   userInfo:nil
                                    repeats:YES];
}

- (void) initializeTimerWithCADisplayLink
{
    _timer = [CADisplayLink displayLinkWithTarget:self selector:@selector(animateBallCADisplayLink)];
    _timer.frameInterval = 2;
    [_timer addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
}