In 1997, in a game between France and Brazil, a young Brazilian player named Roberto Carlos set up for a 35 meter free kick. With no direct line to the goal, Carlos decided to attempt the seemingly impossible. His kick sent the ball flying wide of the players, but just before going out of bounds, it hooked to the left and soared into the goal. According to Newton's first law of motion, an object will move in the same direction and velocity until a force is applied on it. When Carlos kicked the ball, he gave it direction and velocity, but what force made the ball swerve and score one of the most magnificent goals in the history of the sport? The trick was in the spin. Carlos placed his kick at the lower right corner of the ball, sending it high and to the right, but also rotating around its axis. The ball started its flight in an apparently direct route, with air flowing on both sides and slowing it down. On one side, the air moved in the opposite direction to the ball's spin, causing increased pressure, while on the other side, the air moved in the same direction as the spin, creating an area of lower pressure. That difference made the ball curve towards the lower pressure zone. This phenomenon is called the Magnus effect. This type of kick, often referred to as a banana kick, is attempted regularly, and it is one of the elements that makes the beautiful game beautiful. But curving the ball with the precision needed to both bend around the wall and back into the goal is difficult. Too high and it soars over the goal. Too low and it hits the ground before curving. Too wide and it never reaches the goal. Not wide enough and the defenders intercept it. Too slow and it hooks too early, or not at all. Too fast and it hooks too late. The same physics make it possible to score another apparently impossible goal, an unassisted corner kick. The Magnus effect was first documented by Sir Isaac Newton after he noticed it while playing a game of tennis back in 1670. It also applies to golf balls, frisbees and baseballs. In every case, the same thing happens. The ball's spin creates a pressure differential in the surrounding air flow that curves it in the direction of the spin. And here's a question. Could you theoretically kick a ball hard enough to make it boomerang all the way around back to you? Sadly, no. Even if the ball didn't disintegrate on impact, or hit any obstacles, as the air slowed it, the angle of its deflection would increase, causing it to spiral into smaller and smaller circles until finally stopping. And just to get that spiral, you'd have to make the ball spin over 15 times faster than Carlos's immortal kick. So good luck with that.
在1997年,一場法國與巴西之間的比賽, 一名叫Robert Carlos的年輕巴西球員 從35米外發了自由球。 他無法將球直線射入球門, Carlos決定嘗試一件看起來不可能的事: 他的射門讓球繞過球員, 但是就當球快要出界時,它突然向左勾 然後射進球門。 根據牛頓的第一運動定律, 物體運動時會維持相同的方向和速度 除非它受到外力的影響。 但Carlos踢球時,他已經給球施加方向與速度了, 究竟是什麼力量讓球改變方向 並且造就了運動史上最偉大的進球之一? 關鍵就在於旋轉。 Carlos的踢球點在球的右下方, 讓球向右側高飛,但也讓它繞著軸心旋轉 一開始,球沿著明顯的直線飛行, 飛行時兩側的空氣讓球變慢。 在其中一側,空氣與球旋轉的方向相反 導致壓力上升, 然而在另一側,空氣與球的旋轉方向相同, 產生一個低壓力區。 壓力差讓球朝向低壓區轉彎。 這個現象叫做馬格納斯效應。 這種踢球法,也被稱為香蕉球, 在足球場上經常被使用, 而且這也是讓一場漂亮的比賽更加精彩的元素。 但是香蕉球需要極高的精準度 要讓球繞過人牆,然後轉向球門是非常困難的。 球飛得太高,會飛過球門, 球飛得太低,在轉彎前就會落地。 轉彎角度太大的話,進不了球門, 轉彎角度不夠大,會被對手攔截。 球速太慢的話,球會提早轉彎,甚至不會轉。 球速太快的話,球會轉彎得太晚。 同樣的物理理論, 也可以讓一個看來不可能的角球射門成功, 那是一個沒有受到任何人幫助的角球。 馬格納斯效應最初是由牛頓所提出, 他在1670年打完一場網球後,發現這個現象。 這個原理同樣可以應用於高爾夫球,飛盤和棒球。 在每個情況下,都會有同樣的現象。 球的旋轉,讓環繞的氣流產生壓力差, 導致球朝著旋轉的方向轉彎。 現在有一個問題, 根據理論,你可以使勁踢出一顆球 然後讓球飛回你的方向嗎? 可惜的是,不行。 即使球沒有在衝撞中解體, 沒有擊中任何障礙物, 沒有空氣阻力減緩速度, 偏轉角沒有增加, 使螺旋變成越來越小的圓 最後停止。 光是要讓球旋轉, 你需要讓球的轉速, 比Carlos不朽的射門快15倍。 所以,祝你好運。