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.
Godine 1997, na utakmici između Francuske i Brazila, mladi igrač Brazila Roberto Karlos nameštao se za slobodan udarac sa 35 metara. Bez direktne linije do gola, Karlos je odlučio da pokuša naizgled neverovatno. Njegov udarac poslao je loptu daleko od igrača, ali tik pred izlazak iz terena, ona je skrenula nalevo i uletela u gol. Po Njutnovom prvom zakonu kretanja, objekat će se kretati u istom pravcu i po istoj brzini dok se na njega ne primeni sila. Kada je Karlos šutnuo loptu, odredio joj je pravac i brzinu, ali koja sila je naterala loptu da skrene i zada jedan od najveličanstvenijih golova u istoriji ovog sporta? Trik je bio u spinu. Karlos je loptu šutnuo u donjem desnom uglu, poslavši je visoko nadesno, ali i tako da se okreće oko svoje ose. Lopta je sa letom počela na naizgled pravoj putanji i vazduh je strujao sa obe njene strane i usporavao je. Sa jedne strane, vazduh se kretao u suprotnom pravcu od spina lopte, tako dovodeći do povećanog pritiska dok je sa druge strane vazduh koji se kretao u pravcu spina stvarao prostor nižeg pritiska. Ta razlika naterala je loptu da skrene ka zoni nižeg pritiska. Ova pojava naziva se Magnusovim efektom. Ova vrsta udarca, koja se često naziva banana udarcem, često se pokušava izvesti i jedan je od elemenata koji prelepu igru čini prelepom. Ali skretanje lopte sa neophodnom preciznošću da se zaobiđe zid i da se ona vrati u gol je komplikovano. Previsoko i ona ode iznad gola. Prenisko i ona udara u tlo pre nego što skrene. Preširoko i nikad neće stići do gola. Nedovoljno široko i igrači odbrane će je presresti. Presporo i skrenuće prerano ili neće skrenuti uopšte. Prebrzo i skrenuće prekasno. Ista vrsta fizike omogućava postizanje još jednog naizgled nemogućeg gola, neasistiranog udarca iz kornera. Ser Ajzak Njutn je prvi put zabeležio Magnusov efekat nakon što ga je primetio na partiji tenisa 1670. Takođe je primenjiv na loptice za golf, bejzbol i na frizbije. U svakom od ovih slučajeva dešava se isto. Spin lopte stvara pritisak diferencijalan u odnosu na okolni tok vazduha koji skreće loptu u pravcu spina. Evo pitanja. Da li biste teoretski mogli da šutnete loptu dovoljno jako da se vrati skroz do vas poput bumeranga? Nažalost, ne. Čak i kada se lopta ne bi raspala pri udarcu, ili se susrela s nekom preprekom, kako bi je vazduh usporavao, ugao skretanja bi se povećavao zbog čega bi kružila u sve manjim krugovima dok konačno ne bi stala. A samo da biste dobili to kruženje, morali biste da dovedete loptu do spina 15 puta bržeg od Karlosovog besmrtnog šuta. Stoga, srećno s time.