Sometimes the cannon is fixed in position, and other times you have to use the force of firing it to push it into a spot where you can hit the ball.
有时大炮是固定的位置，其他时候你必须使用发射它的力量把它推到一个你可以击中球的点。
2
It is easy to imagine that crashing a spacecraft into the moon involves little more than flinging it in the right direction - much like, say, throwing a ball or firing a missile.
很容易想到，将飞船撞上月亮只需要把它向正确的方向抛出即可——就像，比如说，抛一个球或发射一枚火箭。
3
One landmark is Nintendo’s Wii games system, which is operated by replicating the movements we would make if playing for real: from firing a “gun, ” to whacking a “tennis ball” with a “racquet.”