Friday Funny – backspin, balls, gravity, and the atmosphere

This is some cool science in a video that explains how you can take advantage of something known as “The Magnus Effect” with the application of just a bit of angular momentum, something baseball pitchers have known about for years

From the video comments: The biggest misconception about the Magnus Effect is that it is just a consequence of Bernoulli’s principle. It’s not. This can be demonstrated by varying the surface roughness of the ball. Smooth balls can actually curve in the opposite direction due to the ‘reverse Magnus effect’ because flow over one side is laminar while the other is turbulent. This is a great reference on the shortcomings of Bernoulli’s principle explanations: http://math.mit.edu/~bush/wordpress/wp-content/uploads/2013/11/Beautiful-Game-2013.pdf

Watch:

 

h/t to Harold Ambler

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76 thoughts on “Friday Funny – backspin, balls, gravity, and the atmosphere

  1. I saw these vids. So cool! And I can’t wait for one of you guys to explain to we, a scienctifically novice skeptics how this is relevant to the climate debate (hopefully in layman’s terms).

    • As the byline says, this site is about climate science and anything that interests our host.

      • It is relevant due to possible increased efficiency for ships. It would be nice if you watched the whole video before you comment.

    • Due to using the least refined fuels, ships are big polluters. The video could have done a better job of expressing the need for increased efficiency.I am more concerned about the particulates than C02 or NO2. I hate to use a nasa link but here it is. -http://climate.nasa.gov/news/860/

      • Dennis,
        Yes, ships – generally – use ‘bunker fuel’ that bit of the crack above & below what gets used on the roads.
        At normal [so – UK – temperatures of say 0-25 C – yeah, ish] you can pick up a double handful of our bunkers, and still have most of I with you two minutes later.
        More liquid than the glass used in Medieval cathedral stained glass windows – Yes!
        Than anything else – No, not really!
        Yet ships transport cargo very efficiently – bunkers against tonne-miles . . . . . . .
        Auto

  2. The ball dropped from the dam moved in the opposite direction of the one in the demo. One moves in the same direction as the side of the ball where it is spinning downward, and the other moves toward the side that is spinning upward. What’s up with that?

    • Never Mind. I found another video of the same throw that shows it better. He does put back-spin on the ball. This video appeared to me that he put front-spin on the ball. It was just my poor eyesight.

    • No, both the dam and lab examples are the same. The lab example spends most of it’s time talking about the air flow the same as spin direction but right at the end they show the resultant force carries the ball the other way. This may not be correct but I think of it as the side of the ball with the spin opposite the air flow will increase the friction and thus where the air push will come from.

    • Those of us who saw the movie “The Dam Busters” and read the book of the same title are familiar with this phenomenon, and this history. A tremendous story! Read the book first, then watch the movie, if you have access to both.

      • It’s a fascinating story I’ve been intrigued with since the 60s. Now I have a neighbor (in his 90’s) who was a nose gunner in the bomber that breached the Eder dam. I consider him a hero, but he doesn’t like to talk about it.

      • But interestingly, there is no hint in “Dambusters” that they spun up the bomb in reverse. One is led to believe that Barnes Wallace designed it to just skip like a pebble with ever shorter hops till it came to rest at the dam. But the effect of rotation was important as it kept the bomb in contact with the dam as it samk. It was important to not have a lot of water between the bomb and the dam.
        But historical videos, I have seen since, seem to confirm there was a spin mechanism on the Lancasters used by the 617 squadron.

      • I think when the original film was made, elements of the bomb design were still considered secret, so the film didn’t portray them accurately.

  3. I hardly call one camera shot from one angle to be conclusive of anything. Funny how these “researchers”–who present no credentials, fail to account for the most obvious reason, aside from gravity, that a ball may move: wind!
    A little skepticism is a good thing!

    • I think you will find it was some students having some fun, to see if they could pitch a basket from 400ft up. And they did. And along the way they thought they would demonstrate the Magnus effect, to great effect. And wind is unlikely as a factor, if these were consecutive drops. A commendable effort, I would say, that even surprised the experimentor.
      Its a bit like the astronauts on the Moon with the hammer and feather – a simple demonstration. (One of the most expensive simple experiments undertaken, by the way).

  4. That MIT explanation confuses football and soccer, again (we had this discussion just the other day, dang it).

  5. Great video by Derek at Veritaseum, but his video on climate change is frustratingly based on authority rather than actual evidence.

  6. So I watched the video where the smoke stream stuck to the ball and bent to the right.
    I have no idea who Magnus is or was, but just what is the difference between the “Magnus” effect and the “Coanda” effect which is very well known, and explains how aircraft flaps work to deflect air downwards and create increased lift ??
    Supposedly, Coanda had strapped rockets on the sides of a stick and fabric aircraft.
    So he added some curved (streamlined) metal plates to keep the rocket exhaust away from the skin of his aeroplane.
    Instead, the plates acted as a magnet to curve the exhaust around and set fire to the tail.
    But that might just be an urban legend.
    But the Coanda effect is no legend.
    g

  7. It goes like this,
    Football is American Grid Iron (ellipsoid ball)
    Football is English Soccer (round ball)
    Football is Australian Rules (ellipsoid ball)
    Football is Football (ball of some sort). .
    Regards
    Climate Heretic

    • Handball is a game with a round ball
      Handball is a foul in Football with a round ball.

  8. In baseball, pitchers apply various spin to the ball to make it move around because “a moving target is harder to hit.” The spin may result from the way the ball is gripped, thrown, or released.
    Curves, sinkers, screwballs, and “high heat” all move in different directions because of different kinds of spin applied by the pitcher, who may be either a “fireballing right hander,” or a “crafty southpaw,” at least in standard baseball parlance.
    Some pitchers also serve up the knuckleball, which has little spin due to the way the ball is gripped and released. Lack of spin increases instability, which makes the ball move around erratically as it approaches the plate.
    Finally, there is the spitball, an illegal pitch where some foreign substance like saliva is applied to the ball to alter its flight dynamics, and make it move erratically.
    In contrast to basketball, ping pong players apply top spin to their smashes to make the ball dive toward the table.

    • Didn’t see a thing that I would claim is an aerodynamic effect.
      And by the way; Pakistan did not make the finals of the Cricket World cup, back in March 2015. But Australia did.
      New Zealand did too; but then they didn’t show up for the final; ceding the cup to Australia.
      G

  9. Very cool video.
    There is actually a baseball pitch called gyro ball which done so ball has no magnus effect. The spin is spiral like an American football spin.

    • Exhilarating bowling – reversing it at 90 mph-plus with fantastic accuracy.
      For non-cricketers the theory goes that with a new, shiny leather cricket ball you need to keep one side shiny and the other dull, with the shiny side travelling faster through the air and the ball thus swinging away from the shiny side. The genius of the Pakistanis such as Waqar Younis and the left-armer Wasim Akram was in the way they allowed the dull side eventually to roughen in contact with dry, abrasive outfields, while working away with sweat and spit to keep the other side shiny. Eventually the rough side became the side which travelled faster, with the result that the ball swung into the shiny side rather than away from it.
      This is the “reverse swing” bamboozling the Australian batsmen in the video.

      • Well I wouldn’t be citing cricket as a place to watch balls curve, rather than baseball.
        Not that I’m saying cricket balls don’t curve in the air.
        But with the vast majority of cricket balls bowled, the ball hits the ground before it reaches that batsman. Full tosses are the rarity.
        And any spin imparted to the ball by the bowler, is designed to affect what the ball does AFTER it contacts the ground, not before; excluding the full toss or a Yorker perhaps.
        The Yorker is designed to give the batsman no time to adjust to the ground spin effect..
        As for the effect on a downwind sail, like a symmetrical spinnaker, I don’t know that Bernoulli’s principle or the Coanda effect is the big deal; it’s mostly catching a lot of air mass. The asymmetrical downwind sail still acts like a wing, which makes it hard to shadow with a trailing boat, that works so well with the spinnaker.
        Of course the new wing sails and hydrofoils have turned all the sailing theory upside down.

      • george e. smith, I presume your comment about the symmetrical spinnaker was a reply to my earlier comment that appears below…
        If catching a large air mass was all that is intended when flying the symmetrical spinnaker the top of the sail would be rounded instead of pointed and played out to be equally as far out in front of the mast as the base, effectively becoming a parachute. In fact, a parachute would be used as it would be a lot easier to manage. A symmetrical spinnaker would not be used unless it supplied more forward thrust than a parachute.
        Instead, the pointed top of the sail is pulled tight to the top of the mast while the foot of the sail is played out further forward. This makes the upper tip of the sail the leading edge aerodynamically and the foot the trailing edge. Wind blowing from astern over the top of the sail follows the curve of the sail down to the foot, reducing pressure across the forward side of the sail. This is the Bernoulli effect of the sail that contributes forward propulsion.
        There is also a Coanda effect, as the airflow is diverted directly downward, but it does not contribute forward propulsion in this particular case. Most sails derive forward propulsion from a combination of the 2 effects.
        SR

      • Cricket balls can swerve quite a long way, especially when the atmospheric conditions are right: overcast, high humidity tends to produce the wildest swings. I’ve certainly bowled balls that swing in 18″ in the 19-20 yards before the ball pitches. Movement off the pitch comes in several different varieties.
        A cricket ball has a raised stitched seam about an inch wide. For a spinner, this acts like a tyre when it hits the ground, with the ball spun so the seam is equatorial to the spin, maximising the effect. The degree of diversion depends on maintaining the seam perpendicular to the ground, and sharply angled (even perpendicular) to the direction of motion down the pitch. There are some excellent examples of Shane Warne doing this to Strauss and Gatting in this video that includes slow motion allowing you to see precisely how the ball is spinning:

        As they point out, the movement can be enhanced by taking advantage of the shallow saucer shaped depressions in the pitch caused by footmarks of bowlers. Note the Gatting ball has a sharp swing in the opposite direction to the enormous spin off the pitch – no wonder he found it unplayable. When the seam is angled in line with the ball’s motion, usually a topspinner is produced, which is accelerated off the ground by the spin, which can catch out a batsman who has not moved his bat into position fast enough: topspin balls also tend to skid through lower, dipping as with topspin in tennis. Most spin bowlers tend to impart one direction of spin so the ball moves consistently from right to left or vice versa off the pitch, with topspin for variation. Some can spin it both ways (so called “googly” or “Chinaman” balls), confusing the batsman still further.
        Another kind of movement off the pitch relies on the seam being canted just off perpendicular to the ground, so the seam hits the ground but the ball’s motion means than this applies a torque as the ball pivots around the seam edge until the main surface of the ball hits the ground a tiny fraction of a second later. The direction of motion off the pitch depends on the cant of the seam, and can be to either side of the original motion accordingly. Seam bowling tends to be rather faster than spin bowling: it often aims to deviate the ball just sufficiently so that it just catches the edge of the bat for a catch, or just misses the edge to go on to hit the stumps if the batsman misjudges the degree of deviation.
        The fastest bowlers also bowl “bouncers” – these pitch perhaps half way down the wicket, and fly up chest or head high, partly depending on whether backspin is also applied. The opposite tactic is to bowl a ball at the batsman’s feet (a Yorker), where the prospect of the pain of being struck can frighten them to back away, leaving the ball to hit the stumps – a tactic more common against less skilled batsmen.

  10. Bend it like Beckham.
    Yes real science will have real engineering applications.
    So, back radiation? Radiation from a colder object making a warmer object hotter. Seen any perpetual motion machines running on this phenomena yet? No, I didn’t think so.

  11. The Magnus Effect also comes into play in certain gunnery applications.
    In the WWII B17 Bomber Airplane (and others) there were machine guns pointing out each side of the plane. The barrels had an identical spiral or rifling (to be interchangeable). This meant that bullets traveling out one side of the plane were rotating with the top of the bullet heading into the airstream. Bullets on the other side had the bottom of the bullet rotating into the airstream.
    The guns on each side had a different “drop” (amount of fall per distance traveled) and the gun sights where adjusted differently on each side to accommodate.
    Cheers, KevinK.

  12. For anyone familiar with the game of cricket, there is no better demonstration of the Magnus Effect than this.

    The spin on the ball makes it move both laterally and vertically in the air, and then jag the other way when it hits the pitch.
    It is well dubbed ‘The Ball of the Century’

      • If you look at the other Shane Warne video I posted above, you’ll see the spin of the Strauss ball in slow motion. I’ve been trying to find a link, but I think I remember that it was measured as spinning at 38 rotations per second: a cricket ball has a circumference of 9″, so that’s 28.5ft/sec of sideways bite as it hits the ground, less some slippage. The forward ball speed is given as 51.3mph, or 75.24 ft/sec. The video reveals the ball was deviated by 2 ft in 9 ft, and further deviation of about 11″ in the next 4 ft of forward travel from the popping crease to the wicket. As a batsman you have around 0.1 seconds to react to how differently the ball bounces if you’ve not anticipated it.

  13. This reminds me of way back in the day when I was working on my aero degree. It was gospel that airplanes flew because of bernoulli’s principle (because the science was settled doncha know). One day the physics prof explained to us that this can’t be right, and that it must be a newtonian action/reaction effect, i.e. the wing accelerates a bunch of air downward so you go upward. The newtonian heresy stayed in the shadows for another thirty years, but finally gained enough traction that the FAA started telling instructors that bernoulli was history and they should stop teaching it.
    In hindsight the bernoulli explanation may have just been a hammer/nail problem, i.e. engineers can’t measure the acceleration of a big blob of air but they CAN measure the pressure above and below a wing, so the pressure difference then becomes the root cause, and “settled science”.

    • I don’t think it’s either/or. A wing can deflect air downward at higher angles of attack. Else a plane couldn’t fly upside down. But lift can also be generated by air pressure reduction from the curved upper surface of the wing.

      • My sailing experience has shown me both are used to propel sailboats. Most sails are set to combine varying amounts of “lift” (Bernoulli effect) and wind deflection (Coanda effect). Sails are adjusted for more lift in light wind and more deflection in strong wind.
        However, the symmetrical spinnaker sail operates primarily by use of Bernoulli effects as the direction of air deflection is downward, not aft. Thus deflection of air does not contribute to forward movement except to reduce downward pressure on the bow
        SR.

      • Steve, Note that with the Coanda effect, the airflow is only on one side of the curved surface; the convex side. There is NO assumption of any air flow at all along the concave side.
        Now in most aerodynamic situations such as an airliner’s wing flaps, there is of course air flow over both the underside, and the top side.
        The airflow on the underside, has no option but to deflect downwards, with a resultant lift, and of course also a drag.
        But the air flow over the top would separate from the wing, and become very turbulent, if it wasn’t for the Coanda effect. That effect doesn’t provide all the lift, it just maintains laminar flow of the boundary layers over a much greater surface curvature, that it would absent the effect.
        I believe that the curvature can be explained simply from the velocity shear of the boundary layer air due to viscosity.
        If the upper surface air velocity is taken as positive going from left to right, as for example seen from the near wingtip on a plane moving to the left (airflow to the right), then the wind shear couple as seen from that wingtip, is in a clockwise direction so it has positive angular momentum (right hand corkscrew rule), which causes the downward bending towards the rear.
        If the wind direction over the wing reverses, so does the polarity of the angular momentum.
        So you get positive angular momentum, with positive linear momentum (of the air) or you get negative angular momentum with negative linear momentum.
        The exact same rule applies to the casting of a weighted fly line, using a fly rod .
        The fly line must be launched with its angular momentum matching in sign the linear momentum. ++ or – – . If you try to cast a fly line with either a + – or a – + angular to linear momentum phase mismatch, the line will eventually crash into itself, and collapse on the ground in a horrid mess. Good fly casters are experts at coupling the correct angular momentum imparted to the fly line with the correct linear momentum.
        You end up with a so called “wind knot” in the line or leader if you do it incorrectly.
        It’s not a wind knot but a casting error knot, and experts like Lefty Kreh, for example (or champion caster Steve Rajeff, can make wind knots to order; or not; as they choose.
        I make a few, when I don’t follow the rules.
        The caterpillar tracks on a tank, also follow the correct phase rule. If the tank moves to the right (seen from the observer) which is by convention the positive direction, the track has a positive angular momentum, and verse vicea.
        G now back on track.

    • Dave,
      Thanks for this:-

      One day the physics prof explained to us that this can’t be right, and that it must be a newtonian action/reaction effect, i.e. the wing accelerates a bunch of air downward so you go upward.

      Now let’s see if we can devise a test that proves that this is true.
      What about doing an experiment involving motion in a vacuum?
      How so? Well, replace the moving fluid with a stream of flowing powder falling under gravity, such as we observe in an hour glass sand timer.
      Introduce a convex curved surface (such as the back of a spoon) into the falling stream of powder and observe the deflection of the powder stream by presence of the spoon’s convex surface.
      We then try and pull the spoon away from the flow and measure the force required to achieve separation.
      As the experiment is being performed in a vacuum we can be certain that there is no fluid pressure on the concave side of the spoon.

    • I was taught that aerodynamic lift comes via Bernoulli’s effect and Ram Air pressure effect. The former would be affected by flaps/ailerons as these surfaces change the effective shape of the airfoil. While the later is affected by angle of attack.

  14. Excellent, new effect, to me, very well demonstrated.
    Thanks, though I had to get the video through Youtube not WUWT. Do not know why.

  15. In the late 1990s I stumbled upon a web site hosted by one of the Apple founders where some highly-credentialed physicists and other academics were engaged in a hot debate as to which direction a baseball must spin in order to “curve” in a given direction. I broke in long enough to suggest that they visit a local high-school and simply ask any teen-aged pitcher.
    University-trained scientists have brought us many wonderful advances, but a certain hubris can develop which closes the mind and prevents some of them from seeking out and observing the daily work of real-world practitioners. Despite having thrown many a sinker and slider myself, it was amusing to see how many of those learned men refused to believe that I had any idea which way a thrown ball must spin in order to generate a curved trajectory.
    I wonder how that might relate to climate science?

  16. When I was a high school basketball player in the early 1950’s, the popular theory was that underhanded was the most accurate form for free-throw shooting. In fact, my high school coach required it, except for one very short player. He ended up as one of the most accurate shooters. It wasn’t much later that underhanded shooting became passé.

  17. I like the idea of a soccer match to determine the outcome of the climate debate. They can have Hansen Gleik and Oreskes, we will have Soon in attack, willis in midfield and Monkton in defence.
    our manager would be Anthony and they can have Blatter.
    Mann can sell the hotdogs

  18. Why is it that we hear the impact of the basketball on the surface of the water at the same instant we see the impact, despite the fact that it’s probably around 200 meters away? There should be a delay due to the travel time of the sound. Either there must have been a microphone beneath the dam, or the video editor simply adjusted it. Most likely the latter.

  19. In sec 4.2 of the MIT pdf, Bush also talks about a reverse Magnus effect. He and his associates kicked smooth beachballs with the right instep, and noted & plotted the balls curving to the right. After wrapping an elastic band around the ball’s equator, the ball now curved to the left, as expected from the Magnus effect. See fig. 17.
    “…this results from the difference in the boundary layers on the advancing and retreating sides, the former being turbulent, the latter laminar…”
    Ping-pong players everywhere are puzzled, as the very smooth balls used in table tennis behave exactly as would be expected from a plain, ol’, everyday Magnus effect, as anyone with any kind of forehand or backhand smash well knows.

  20. When I studied the Bernoulli Principle in Physical Chemistry class, I was impressed by the *assumptions* inherent in the derivation of the equation: (1) the gas is assumed to be confined to a tube of finite cross-section, (2) the flow of the gas is always laminar, (3) the gas has negligible viscosity, and (4) the texture of the surface is irrelevant. These assumptions are (1) mutually incompatible, and (2) only approximately realized at low pressure and low flow rates for ideal gases.
    I realized immediately that the application of Bernoulli’s Principle to airfoils violates *all* of the assumptions, and therefore amounts to ‘smoke-and-mirrors’. I looked around and the only phenomenon I could find that made sense in context is the Coanda Effect. The Coanda Effect and the Magnus Effect seems to be closely related.

    • They both involve separation/attachment of boundary layers so the effects are related. The reverse Magnus effect is observed under laminar flow conditions. The Coanda effect is caused by the attachment of a fluid jet to a curved surface and consequent deflection downstream. Surface effects due to the surface roughness involve the difference between the laminar and turbulent boundary layers.

      • Any thoughts on Bush’s experiment with the smooth beach-type ball, reverse Magnus effect, and everyman’s observation of the behavior of smooth ping-pong balls?

      • Depends what you want to know, in the case of smooth balls it’s possible to get the case where the boundary layer on one side of the ball is laminar and on the other is turbulent. As a result the normal differential separation of the boundary layers is changed giving rise to the reverse Magnus effect. Interesting effects arise when the ball is accelerating or decelerating as the trajectory can start with a normal Magnus effect due to both sides being turbulent (or laminar), passing through a transitional phase when one side changes and so the reverse Magnus effect occurs, and then reverting to both sides being laminar (or turbulent) when the normal Magnus effect occurs. Light balls such as ping-pong balls deviate much more noticeably. Surface roughness can induce a variety of effects e.g. the effects of seams on the trajectory of cricket balls and baseballs.

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