The Physics Behind a Curveball – The Magnus Effect

The Physics Behind a Curveball – The Magnus Effect

Articles Blog


[SQUEAKING] [POP] We were at this
event the other day. Yes! Yeah! Woo! And I saw a guy kick a ball. MEN: Goal! I was distraught over the
curved trajectory of the ball. MEN: Goal! How do they do that? And since you can’t get good
at soccer using physics– MAN: Oops. –I’d better consult a friend. Kyle! [WHOOSH] Kyle, I wanna to
be able to bend it. OK. OK, so look. I bet you that I can take this
ball, set it in that corner, and bend it into that goal. So I’m skeptical about
this because you can’t even see the opening of the goal. All you can see
is the goal post. And from the vector that you
trace from the corner to– [CLAP] It’s magic. No, it’s physics. Do it again. [GROAN] [CHAINS RATTLING] How did you do that? Well, it’s a pretty
standard technique in soccer. You use the inside of your foot
to generate spin on the ball. That spin is actually
going to make the ball curve into the goal. Let’s take a look
at how that happens. As Kyle kicks the ball with his
right foot on the right side, he imparts a spin on the ball. The ball traveling
in this direction means air is flowing across
it in the opposite direction. But right near the ball,
there is a thin layer of air dragged around. As oncoming streams
of air pass the ball, the side moving in
the same direction as the spinning
ball is accelerated follows the curve of the
ball and is deflected off to the right. The side that is moving
against the spinning ball meets opposing air and can’t
continue around the ball. It slows down and goes straight. We end up getting a net
flow of air to the right, and the ball must move left. Wait, wait, wait. That’s Newton’s third law. Yes, thank you, Kyle. Just like a rocket, if you
push a gas one direction, namely downwards
out of the rocket, then the rocket has to go up. So what you’re saying is
my shot is like a rocket! (LAUGHING) Yes,
thank you, Kyle. Like the rocket, as the
air moves in one direction, the ball has to go
the other direction. Also, since the air is slowing
down on the right side, you get a buildup of air,
which creates a higher pressure on that side and
pushes the ball to the left. The airflow is
extremely important. You could not make
this kick in a vacuum. It’s not some weird thing the
ball does to itself to curve. You need air flowing across
the ball to push the ball. This is called
the Magnus effect. So you can use this
phenomenon to do all sorts of shots in soccer. As we already saw, I can
use the inside of my foot to make the ball curve left. I can also use the
outside of my foot to make the ball spin the other
way, and then it curves right. If I wanted to, I could even
hit the bottom of the ball, give it backspin, and
send it up into the air. With a backspin, it’s
actually gonna curve upwards. Finally, if I wanna
get real tricky with it, I could put no spin on it
at all, like a knuckleball. When this happens,
you get turbulence, unpredictable on both
sides of the ball. And the keeper doesn’t
know where it’s going. DIANNA COWERN: Should
we try the knuckleball? That one’s gonna
be a little tougher. [WHOOSH] That’s the physics of soccer. Thank you for your help, Kyle. [SMACK] If you wanna see some videos
of some incredible soccer players bending the ball,
check out these links. [THEME MUSIC] [THUNK] [DING] Oh! [THUNKING] Oh, no! [DIANNA GASPS] [THUNKING] Oh, no! [THEME MUSIC]

100 thoughts on “The Physics Behind a Curveball – The Magnus Effect”

  1. @physics girl Since the goal post bar is curved, when the ball hits it, it applies a reaction force at an angle and the same phenomenon(magnus effect) happens again and hence it hits again the goal post!

  2. Hope you soon will get a very high speed camera, that would be so usefull on this phenomenon! I like so much what you do, keep this amazing way !!

  3. Gravity LOL! No the ball still had the same spin as it needed to make the initial hit, but increased from the first contact with the net. This increased the spin/ curving effect, and caused the second hit.

  4. Thanks for the vid 🙂 Is it possible for the airflow to be so fast that the Magnus effect is no longer present? I think it would still be present as you would still have different relative air speeds either side of the object, but I've people say otherwise. Do you have any thoughts on this? Thanks 🙂

  5. I still don't understand how the knuckleball works.. in baseball, the knuckleball effect happened due to the seam of the ball.. in soccer, the ball is smooth and seamless but some soccer player can make it happen.. why and how?

  6. On that last close call, the ball rolls against the goal. This plus the spin put on the ball by Kyle's foot makes the ball curve twice and it bounces again.

  7. Well here's the explaination : the ball corves towards the LEFT, because it's spinning Counterclockwise. As it hits the beam, it bounces off at an angle equal to the angle of incidence (the angle of incidence is measured between he imaginary line that the ball travels on…in this case it's a curve, instead. we use the tangent and the perpendicular line on hat surface, within the same plain as the trajectory. And the angle of reflection is the same – equal. ) So the ball bounces off at an angke, but is still has some angular momentum (it's still spinning) and it curves to the lefy again, and it hits the bar again, then it bounces off for the last time, as it's treveled past the gate and cannot hit anything else on the way down to the ground.

  8. Oh and with that last kick the ball still had a spin too it so the air kept pushing it to the left causing it to hit once again. like a frisbee against a wall.

  9. Great video.. But it would be better if you explain it with the Bernoulli principle. This is a great opportunity to introduce that.

  10. As you stated the ball is using the wind to curve so when it curve it hit the post and still had some of that spin so the post kind of made a artificial curve ball kick and curve it to hit the other post

  11. In The Last Kick When The Ball Bends And Hits The First Bar The Movement In The Left Side Cancels Out And Only The Movement In Forward Direction Remains Unchanged And The Ball Keeps Moving In Forward Directions And Hits The Second Pole , Is The Reason Correct @Physicsgirl ??

  12. Where is the mathematics model? I want to know the correlation between the bending force generated and spinning speed or ball speed. (ball friction assumed to be constant and the ball is perfectly round)

  13. The Magnus Effect was overwhelming so even though it hit & bounced off the goal the first time it still wanted to curve that way, plus while it was spinning counter-clockwise its spin may have accelerated by "gripping" the goal a bit.

  14. the ball still had the curve on it when it bounce off the goal the first time and it curved back only to bounce off again!😉🙋⚽

  15. The ball still had the force of the air so it curved and when it hit the goal post it still curved so it hit it again

  16. Well, the ball hit the goal twice due to the same principle you were explaining. When it hit the goal post for the first time it gave so much more spin that the ball was able to make a second and sharper curve. That's my hypothesis xD. Love from Panama, love science 😀

  17. My explenation to that last kick is that after it bounced off the pole it was still spinning and was in straight line so it kept going left
    Done how easy was that

  18. God! You're beautiful, you're smart, and you trully appreciate football! I'm the freekick specialist of my team so, yeah, thanks Magnus! Although it is kinda obvious when you make a free body diagram and analize it's forces, most people never think about the physics behind sports. It's either luck, guts, good physic or skills for most people, but never something that can be actually measurable. Thanks for the vid!

  19. Note to self: If I score an Olympico, I'll honor Physics Girl in my celebration… also the Roberto Carlos free kick (aka the first link) is considered to be the one of the greatest free kick of all time

  20. the ball goes in the direction where air is accelerated you just said opposite … if ball turns from left to right high pressure is on the left the ball will go towards the left and not in the opposite direction of the high pressure side..

  21. Andrea Pirlo built a legend on this Magnus Effect: his most letal kick – "la Maledetta" (the Cursed)- is a goalkeeper's nightmare!

  22. To achive something close to a knuckleball you have to hit the ball with the tip of your foot.
    Note that it's strongly discouraged by any coach or trainer worth anything because the ball won't chage its general direction, so it's useless to get around an obstacle like a wall or a defender; it's just makes the ball move erraticaly while it goes forward so much that it would actually decrease your chance of scoring

  23. Great as usual! Suggestion: I have never had the opportunity to get an explanation as to why I still need my distance glasses to see clearly an object in a mirror that is lose to me.

  24. i vaguely made this connection when reading about the magnus effect on wiki.

    Expected to see a baseball though…

  25. looks more like the air is pushing against the ball on the right side; as opposed to simply flowing past it as described

  26. I curved so many soccer balls in the past, but now I see it more as a science now because you literally have to take into account of the wind and the defenders trying to prevent you from actually curving it so. Its sort of tricky to do it in a game but you can do it

  27. Sad thing is… I argued with a friend last night that only the wind can cause a change in direction of a moving ball. Screw you, magnus effect.

  28. Why's Kyle scared of trying the knuckler? Those aren't that tough. Also he forgot to mention top spin to cause the ball to sink more than expected.

  29. The ball has to be in a certain form-factor too. Right?
    Something about 'if it has less "sides", it spins the opposite direction'
    And more curve, if it has these "dents"… like… what are they called?

  30. The analogy to rocket propulsion is *incorrect*. A rocket moves forward because it ejects matter backwards. As a reaction force, it is pushed forward. The ball turns because (like you said) its spin creates a depression, that will cause the ball to move to the lower pressure area.

  31. Not spinning in the air. The air doesn't move. The arrows represent the two sides of the ball.
    –>
    O
    –>
    Spinning clockwise in the air.
    –>–> (drags air along. Air and the side of the ball both move to clockwise now)
    O )
    –><–/ (pushes air)

    This is a really cool video! The ball drags along some air, and because it's spinning the same direction than the ball, it accelerates and bends following the direction the ball is spinning. So the ball pushes the air from the other side and causes it to force pressure towards the originally still air which slows that side down.

  32. The "knuckle ball" is a great examples of the (Theodore) Von Kármán vortex steet.

    Vortex shedding is also very common in volleyball and less common but still used in baseball.

Leave a Reply

Your email address will not be published. Required fields are marked *