That's where power and topspin come in.

就是力量和上进入的地方。

Since a curveball has topspin, that means the air behind it gets deflected upwards.

由于弧线具有上， 意味着它后面的空气向上偏转。

Man wouldn't know topspin if it hit him in the ball sack.

被击中下身才知道上的厉害。

However, it has a high topspin, and it's awkward to return.

但是它的上高，回难。

But topspin serves are more accurate and still difficult to return.

但上发更准确，而且仍然很难回击。

That's why Serena also uses topspin to her advantage, usually when her first power serve goes out of bounds.

就是为什么小威也利用上来发挥自己的优势，通常是在她的第一次强力发出界时。

That's because the topspin on the ball forces it to drop sharply right before it reaches the opponent.

是因为的上迫使它在到达对手之前急剧下降。

So, Serena could be about to deliver a topspin serve, a power serve, or even a slice serve.

因此，小威可能发出上发、强力发，甚至是切发。

For example, Serena's average topspin serve is about 145 kilometers per hour, 25 kilometers per hour slower than her power serve.

例如，小威的平均上发速度约为每小时145公里，她的强力发慢每小时25公里。