A curveball is one of soccer’s most spectacular marvels!
When you see a winger curve a cross right to his teammate’s feet across the last defender, or you see a striker bend it like Beckham on a freekick, you stand in utter awe.
And you wonder whether the player even intended for such a meticulous curve in the first place. Because if he did, how could he have known how much or when the ball was to curve?
Well, that’s where soccer meets physics!
And physics tells us that the spin on the ball, the pressure of the air around the ball, and the ball’s surface all get a say in how much, which direction, and when the ball will curl.
What you know as the in-swinger, out-swinger, knuckleball, or dip are all backed by laws of physics. And so, it’s not just a fluke when a soccer player puts the right amount of curl in his shot.
There’s tons of practice and a good understanding of these dynamics that enables soccer players to execute such balls.
So, let’s get into why a soccer ball changes direction midair and how you can use the same mechanics to learn these shots!
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Why Does a Soccer Ball Curve?
A soccer ball curves or deflects from its straight path based on three principles. It depends on either the spinning of the ball, the air pressure around the ball, or the surface of the ball.
In simpler terms, it’s how much spin you initiate before the shot, the part of your foot you take the shot with, or the type of ball you’re using.
Still not simple enough?
The following walk-thru of these principles in detail should then clear things out for you!
Magnus Effect (Spinning Ball)
When the physicist El Padrino, Isaac Newton observed a tennis ball dip with a topspin, he discovered a principle now popular as the Magnus Effect.
Cutting to the chase, it means a spherical or cylindrical object will curl towards the direction of its spin through air or liquids. And though the scientific phenomena are less understood, it is widely practiced across several sports.
A baseball pitcher puts an aggressive spin on the ball while pitching to swing it in the air. The direction the ball goes in depends on the direction the pitcher spins the ball in.
Coming back to soccer, the soccer ball mimics the same theory. An inside-foot shot by a right-footed player will always initiate a counterclockwise spin and will curl the ball to the left.
And an outside-foot shot will initiate a clockwise spin and curl the ball to the right. The same applies to left-footed players, though with opposite directions.
It happens because the air seems past a soccer ball at different speeds to either side when it is spinning.
For a counterclockwise spin, the speed of the air past the ball on the right side is much greater than it is to the left. This forces the soccer ball to follow a trajectory path of the least resistance.
And in practice, you see the ball curl in the opposite direction you spun it in.
Can’t relate it to a soccer kick in practice?
If not, then refer back to Roberto Carlos’s historical freekick against France in 1997. It was an outside-foot spinning shot that curled left and found the back of the net!
Example
When you talk about curlers and swingers, you’ve got to talk about the best in the game. And David Bekham’s screamer against Greece in the 2001 World Cup to rescue England stands out the most!
He curled the kick rightly past the defending wall after being awarded with a freekick in Beckham territory. And left the goal keeper helpless as he breathed air into the Old Trafford crowd.
Pressure Displacement (Knuckle Ball)
Another not-so-common curveball in soccer is the knuckleball. Difficult to execute, it was unofficially introduced by Manchester’s Christiano Ronaldo of the 2000s.
Besides being loaded with ridiculous power, the ball curves in the air even though it’s not spinning. It is a sure way to trick a goalie, but let’s first see how it works!
Knuckleball kicks are mostly power shots that are at a slight angle from the center of the ball. As soon as the ball begins motion, the pressure inside the ball shifts to the opposite side.
So, if you were to kick a soccer ball slightly to the left of the center with the knuckle of your foot, it would build pressure to the right side of the ball.
And to maintain an equilibrium, the air pressure on the ball increases outside on the left side of the angle you kicked the ball from.
This then forces the ball towards a path of less resistance to the left side. And this happens similarly for any angle to the center you shoot the ball from.
To make the ball curl right, your point of kicking should be slight to the right of the center. And a kick slightly below the center of the ball will make the ball dip in midair.
Example
One may think of many perfect knuckleballs but none come close to Ronaldo’s rocket shot against Arsenal in 2009 from 40 yards out.
The commentator’s remarks changed quickly from “…it’s impossible for even Ronaldo to think about it…” to sheer disbelief as young Cristiano dipped the ball just enough to slip past the keeper.
The freekick had a ton of power packed into it and went with a principle similar to a top spin, making it dip right at the end.
Reverse Curl (Flat Surface)
Every four years, when the champions from around the world take on the field, they lift spectators on every freekick.
And as more and more freekicks fly past the goal, the pundits and coaches bring the blame on the “new” ball. While this is usually an Alibi for disaster, the Jabulani showed us that there might be truth to these claims.
The 2010 World Cup ball was the first one ever to feature an advanced design and smooth surface. And it was the smooth surface of the ball that made it go in unpredictable directions.
Think back to Andrea Pirlo’s freekick against England in the 2014 World Cup!
Research then showed that the same Magnus effect that made a soccer ball curl in a direction a player wanted makes the Jabulani go in the opposite direction.
A rough surface favors the laws of the Magnus effect, whereas a smooth surface opposes it. Seeing how soccer balls had always been stitched in pentagons and hexagons before, they never faced the problem.
But on the newer Jabulani or any smooth surfaced soccer ball, if you kick it with a counterclockwise spin, the ball might even curl to the right instead of left.
This technique is now more commonly known as the reverse curl ball. Though it is equally unpredictable for the freekick taker, it is a sure way to confuse the goalkeeper!
Example
There’s no better example to this one than Andrea Pirlo’s thunderous strike against England in the 2014 World Cup.
Pirlo packed the shot with a pinch of spin to curl it to the right. But as the ball gained some height, it flicked and changed direction rapidly.
Joe Hart was saved by the crossbar as the ball bounced off of it and into the stands. But results aside, it was one of the first moments that drawed in the critics to question the design of the Jabulani.
The Wind!
You may not have thought about this to make it on the list here. But the wind speed and direction influences a soccer ball more than you think!
The wind will force the ball to curve in its direction. It will dip the ball if it’s moving opposite to the wind’s direction.
Lift it further if moving along with it. And move it left or right if the wind is moving sideways to the ball’s trajectory.
Piece of cake!
Example
And to clear any doubts about the wind influencing a soccer ball, look back upon Tim Howard’s 100 yard goal vs. Bolton.
The ball flew past the field and found the back of the net with an elastic bounce on the top of the opponent’s D.
More than that, Roberto Carlos admitted himself that his phenomenal banana curl against the Frenchmen in the 1997 World Cup was a wind-assisted fluke!
So, if you see a lad bend a mighty curler on a windy day, think twice before you praise the guy for his talent!
Conclusion
The rules of physics apply to everything around us, and soccer is no different!
What you’ve known as crafty kicks before having a solid scientific explanation for their trajectory. And to sum them up, they depend on either the spinning of the ball, the pressure around it, or its surface.
You’ll now observe these kicks more closely after learning the above dynamics behind them. And even get better at practicing these kicks now that you know the science behind it!
Hi there, I’m Jay.
Soccer is everything in my life! My friends and I have created this blog with all our enthusiasm, passion, and understanding after years of playing pro soccer. Hope you will enjoy it!