68 Soccer-Low

Soccer FOCUS Question How do different forces affect the movement of a soccer ball?

足球焦点问题不同的力如何影响足球的运动?

Physics Gets a World Cup Crowds are cheering and waving flags from around the world. What sport are they watching? Soccer! Every four years, soccer teams face off to compete in the World Cup. It is an exciting game and a thrilling tournament! Soccer is a game of skill and endurance. It is also a game of physics. Physics is the science of matter and energy. Physics explains the speed and direction of the ball. Physics also explains. why a ball can curve around players. Maybe the World Cup of soccer should be called the World Cup of physics!

来自世界各地的人们欢呼雀跃，挥舞着旗帜。 他们在看什么运动? 足球!每隔四年，各支足球队就会在世界杯上展开角逐。 这是一场激动人心的比赛!足球是一项技术和耐力的运动。 这也是一场物理游戏。 物理学是研究物质和能量的科学。 物理学解释了球的速度和方向。 物理学也解释了这一点。为什么球可以绕着球员转。 也许足球世界杯应该被称为物理世界杯!

Playing the Game Soccer is a team sport. During a soccer match, the eleven players of one team try to move a ball down the field and into the goal of the other team. The other team tries to do the same thing in the opposite direction. Newton's first law of motion explains how a soccer ball moves. According to this law, a moving object keeps moving until a force acts on it. Also, an object that is not moving stays at rest until a force acts on it. When a soccer player kicks a soccer ball, she applies force to the ball. Will a moving soccer ball keep going forever if no one touches it? Of course not! Forces act on the soccer field. These forces affect the motion of the ball.

足球是一项团队运动。 在一场足球比赛中，一支球队的11名球员试图将球从场上移到另一支球队的球门。 另一队试图在相反的方向做同样的事情。 牛顿第一运动定律解释了足球如何运动。 根据这一定律，一个运动的物体一直在运动，直到有一个力作用在它上面。 同样，一个不运动的物体保持静止，直到力作用于它。 当一个足球运动员踢足球时，她对足球施加了力。 如果没有人碰一个移动的足球，它会永远运动下去吗? 当然不是!力在足球场上起作用。 这些力影响球的运动。

Soccer Balls That Go Up Must Come Down Sometimes, a soccer ball moves on the ground. Other times the ball flies through the air. What keeps a kicked soccer ball from flying straight out into space? Gravity is the force that pulls objects toward Earth's surface. It pulls the soccer ball back to the ground. Air resistance is the force of air pushing against a moving object. It pushes against the flying ball, slowing it down. A soccer ball that is kicked up will eventually come back down to the ground.

有时，足球在地面上运动。 其他时候球在空中飞。 是什么让踢出的足球不直接飞向太空? 重力是把物体拉向地球表面的力。 它把足球拉回地面。 空气阻力是空气对移动物体的推力。 它推动飞行的球，使其减速。 一个被踢起来的足球最终会回到地面。

Acceleration Not every kick makes the ball go fast and far down the field. Some kicks move the ball just a little bit. The ball may move from side to side. When players dribble the ball, they make small, controlled kicks. This keeps the ball between their own feet and helps them move it around the field. Acceleration is the change in an object's speed or direction of motion. Newton's second law of motion says that acceleration is related to how much force is used. A small kick leads to small acceleration. The ball moves just a little. Dribbling uses small forces. During a big kick, a large force is applied. The acceleration will be large. This moves the ball farther than small forces do. Think About It How can you tell which player on this page is applying a larger force?

并不是每一脚都能让球飞得又快又远。 有些踢法只是稍微移动了一下球。 球可以从一边移动到另一边。 当球员运球时，他们会进行小而有控制的踢腿。 这样可以保持球在他们自己的两脚之间，并帮助他们在场上移动。 加速度是物体速度或运动方向的变化。 根据牛顿第二运动定律，加速度与所使用的力有关。 小的踢腿导致小的加速度。 球只移动了一点点。 盘带需要很小的力量。 在大踢腿时，会施加很大的力。 加速度会很大。 这使球比小的力移动得更远。 你怎么知道这页上哪个玩家用的力更大呢?

Kicks and Curves One of the most famous soccer plays of all time was a free kick by Brazilian soccer player Roberto Carlos. A free kick starts the game again after it is stopped for a foul or another reason. What made the free kick by Carlos so famous? The ball curved around a whole group of players and flew right into the goal! How did the ball curve around the players? The force of the kick made the ball move forward toward the sideline. But because the ball was spinning, its motion changed due to the Magnus effect. This caused the ball to curve.

历史上最著名的足球比赛之一是巴西足球运动员罗伯托·卡洛斯的任意球。 任意球在因犯规或其他原因被停止后，将重新开始比赛。 是什么让卡洛斯的任意球如此出名? 球绕过一群球员，直接飞进了球门!球是如何在球员周围弯曲的? 那一脚的力量使球向前移向边线。 但由于球在旋转，它的运动由于马格努斯效应而改变。 这导致球弯曲。