How to hit a knuckleball like a boss?
Eight words many young footballers have probably typed into YouTube or a search engine.
Cristiano Ronaldo is arguably the most famous player to have used it, while Brazilian icon Juninho was one of the first stars to introduce the strike to the modern game.
Read more: Concussion in sport: Belfast speaker says more is needed to protect athletes
The knuckleball first became famous in baseball, but the scientific development of balls means it can now be done in football.
And one man knows all about the science behind it is Mark Langtry.
A former League of Ireland player, Mark also has a degree in physics and is bringing his extensive wealth of knowledge to Belfast next weekend when he will host a special talk at the NI Science Festival.
Mark will take his audience on a highly interactive investigation into the science and technology behind football.
Belfast Live caught up with Mark ahead of his talk at Girdwood Community Hub on Saturday, February 25.
We chatted about how science has impacted on sport in recent years, and how the official World Cup match ball was designed by scientists and trialled at NASA.
Mark also explained the evolution of the free-kick in football, and how a knuckleball actually works.
Here's what he had to say:
BL: Hi Mark. How much are you looking forward to visiting Belfast again?
ML: "I can't wait to visit Belfast, especially the NI Science Festival which I have been attending for over a decade. Probably since my student days.
"I love Belfast, the people and the vibe created at the festival."
BL: You have played football here before?
NL: "I played football at the Milk Cup, as it was known back then. I played in that twice, and also in the League of Ireland I was up in the Setanta Cup.
"I have had the experience of northern football, for sure."
BL: Tell us a bit about football physics? What is it all about?
ML: "Football physics is all about the role of science and tech to make footballers better, and how players can use science to improve their performances.
"So we explore all this at the show. We can assess how fast you can kick the ball, how high you can jump or how quick you can move. Even how strong your hamstrings are.
"And we involve loads of people so it should be a great event."
BL: Sports science and technology is massive now...
ML: "It can be the difference between winning and losing, and top sports teams know this. It is a business, and the business is winning.
"They will use anything they can to give them a competitive edge, and science gives you that. So you just need some athletes or teams to start using sports science to improve themselves.
"You can make them faster and stronger, and also find out when players fatigue, how close they are to sustaining injuries. And then clubs can adapt their training around that.
"Science can give clubs and athletes insights into performance, and it clearly works, especially in the world of football.
"Even League of Ireland teams, and top schoolboy teams, use science to make the difference in performance. Information changes the situation, and the more information you can give players and a team, then the better for them.
"I think everyone these days knows that and they are really hungry to use science tech."
BL: There are a few top sports technology companies on the island of Ireland. They are leading the way...
"ML: There are a lot of sports science companies in Ireland who are world leading, like STATSports and Oracle. I have a piece of equipment which is designed by a former GAA player which is able to analyse the strength and force of your hamstring.
"The most injured muscle in the body is the hamstring. Being told 'it feels a bit tight' doesn't cut it for Manchester United.
"Now there is testing equipment which can put numbers and data into performance so you can make the right decisions for your player."
BL: Let's get down to the main topic. Every kid playing footballer has probably watched YouTube videos of the knuckleball. Have you any tips?
ML: "The knuckleball is something we investigate in the show! We also look at how you curl the ball, bend it like Beckham.
"And that's actually something called the magnet effect, and it is named after a German scientist who investigated how cannonballs shoot out of a cannon on a battlefield.
"The cannonball kept curling and missing the target, and he discovered it was because the cannonball was spinning. And that's how you curl a football, by making it spin.
"With the knuckleball, it is all about hitting the ball with little or no spin. And that's why these players take these strange run-ups, because it is difficult to hit the ball dead centre.
"You end up kicking under the ball or to the side. So players try to kick the ball dead centre with little spin as possible, and it has a dramatic effect.
"Physicists study these things. I have studied the flight of footballs, and during my physics degree I was able to bring together my love of football and physics, and assess how a ball moves through the air.
"I also looked at how they design footballs, and the changes they make to do the things we see. They discovered that if a football is in a wind tunnel and is moving fast but not spinning, then it gets very strange and unpredictable air flow around the ball which causes it to move in different directions. And you can't predict its movement.
"So that was called the knuckleball.
"It existed in baseball many years ago, and the advance in the design of footballs has meant that the speed at which the knuckleball should happen has come down to speeds that are common in football.
"So the design of the ball has made this possible, instead of just baseball.
"And when it is used by players like Ronaldo or some of the free-kick specialists, well you see the knuckleball in action.
"It is a completely erratic movement, but it is a great link from real physics to football. And every kid is trying to do it."
BL: What about kicking the ball on the valve?
ML: "Many kids think you have to kick the valve. They think that has something to do with the flight of the ball, but it has nothing to do with it.
"Players align the valve to use it as a target to kick, so they can kick the ball as near the centre as possible. That's a guide to make sure they kick the ball on that spot.
"So you could position the ball in any shape you want, but it is all about hitting the ball as near the centre as possible."
BL: You should be an expert at this. Is performing a knuckleball harder than the science suggests?
ML: "In practice, it is extremely difficult. It is very complex mathematics and physics.
"Anything that moves through the air, it is complex mathematics. So after studying free-kicks, like that Roberto Carlos one and the knuckleball one, it is very mathematical.
"Scientists do the work and pass on the information and data on to teams in a simple way. They will let teams and athletes know how they can practically use it."
BL: The football free-kick has really evolved over the decades...
ML: "It has. From the curling free-kick to the Roberto Carlos one, and then knuckleball. And it is a small example of players using science to achieve an edge.
"There is also the nutrition side of things, and what exercises players should be doing, and how often. Even psychologists work on athletes' mindsets so they make the right decisions, and quickly.
"There is a whole diverse range of scientists to make a player as good as they are. People think sport and science are two different things, but they are linked in so many ways.
"So the more you learn, the better you can be at whatever you like.
`"Technology is becoming more useful as well. Most people wear smart watches now to see their heart rate, steps etc. And it is helping us become fitter.
"Even people are jumping into bins full of ice cold water. Anything to give you that wee bit extra will lead to people trying anything.
"But there will be no cold water at the show!"
BL: Even the design of a football. Are scientists involved in that?
ML: "There are people whose job it is to design the World Cup football for Adidas. I linked up with these people who are physicists and studying what I was studying, but they were designing the World Cup ball.
"They had this great example in 2010 when scientists tried to design the roundest football ever called the Jabulani. It was an absolute disaster. The ball was flying like crazy and the players and goalkeepers were going mad.
"They discovered that a rounder ball doesn't make it a better football. It is actually the roughness of a ball that makes it fly through the air better. Just like a golf ball uses dimples.
"I have the official World Cup ball from Qatar and it is covered in notches and dimples, which is to help the air stick to the ball better.
"So I worked with the guy who was designing the ball for the past couple of years. They looked at things such as how many panels they use, what shape are those panels, will they stitch them together and use dimples?
"And they actually take this to NASA's testing facilities, and put footballs in wind tunnels. They send a report to Adidas with their design for the ball.
"And it is the same for football boots. Scientists and engineers design them. The new boots almost have rubber ridges on them, in specific patterns. It is to help you spin the ball better."
Mark Langtry - Football Physics' takes place at Girdwood Community Hub on Saturday, February 25. A full list of events at this year's NI Science Festival can be found here
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