Talk:Magnus effect/Archive 1

Archive 1

Although discovered by Heinrich Magnus in 1853, it remained little studied until the 1920's and 1930's. Most all of the research was done in Germany. The Magnus Effect force can be very powerful, and was studied first and utilized in hydrodynamics, and then came aerodynamic utilization and measurements. Probably the best book written on the subject, in order to understand it, was By Anton Flettner in a translation published in the U.S. ( see Wikipedia discussion under "Anton Flettner". Also: "Applied Hydro- and Aeromechanics," by L. Prandtl and O.G. Tietjens, McGraw-Hill Book Company Inc., 1934.
Note: Anton Flettner was the first to use rotating cylinders to produce Magnus Force to drive a wind driven ship. Also noteworthy, was the fact that this was the only sailing ship that could be driven in reverse - simply by changing the rotation direction of the cylinders!
Note: See also the NASA web site that discusses the Kutta-Joukowski lift theorem, which explains the Magnus Force and provides an equation to estimate its magnitude. This site also mentions the Flettner-proposed wind driven ship that used an engine to spin a cylinder. (A picture of the ship is shown.) It further notes that: "the propulsion force generated was less than the motor would have generated if it had been connected to a standard marine propeller!" NASA Glenn Research Center Stephreg (talk) 20:42, 30 July 2006 (UTC)

Tennis

About this phrase in today's copy of this article, "Isaac Newton described it and correctly theorised about the cause 180 years earlier after observing tennis players in his Cambridge college." -- where does it say tennis was available during Issac Newton's time? The Tennis article says otherwise. Was a tennis-like game available, and what was it called? Mdrejhon 20:30, 19 June 2007 (UTC)

Not to worry i think. Tennis has been around since the early 15th century. You see it mentioned in journals and chronicales contemporary with Joan of Arc, for example. That said, the kind of ball being used in Newton's day would have been quite different. The game was still court tennis then. The "modern" game of tennis is lawn tennis - adapted for play outdoors on something like a putting green in the 1870's. But it was still "tennis" before that. Restricted to the upper classes as "court tennis." Ken2849 15:56, 20 September 2007 (UTC)

Turbulent/laminar flow

"This is not the only way of describing the Magnus force. The separation of the turbulent boundary layer of the flow from the ball is delayed on the side that is moving in the same direction as the free stream flow, and is advanced on the side moving against the flow..."

The wording here implies that there are two complementary explanations of the same force (velocity difference and boundary separation). However, I wonder if they are actually two independent physical contributions to the force (i.e. two additive forces), and not just different descriptions of the same phenomenon? If so, the text is misleading. Mtford 07:54, 5 October 2007 (UTC)

It remains the case as Mtford pointed out 5 years ago that the main article is not certain what the cause of the Magnus effect actually is, is it explicable by laminar flow, consistent with the diagram or is it due to boundary layer separation and turbulence. The former is understandable but not "likely" as the article says, the latter is more in keeping with the conventional understanding of real-world fluid flow but there is no detail and it is scarcely understandable. The diagram and article Jeffareid links to, see below, could be a good start but it looks incomplete to me. There is not anything obvious and better on the net turning up on a quick search. rdurkacz 19:14, 11 January 2013 — Preceding unsigned comment added by 180.181.200.37 (talk)

A better description of Magnus Effect

Here is a link that offers more on flow seperation of Magnus Effect, with a better diagram (although deflection of flow is exaggerated, it does at leas show a deflected flow).

http://www.geocities.com/k_achutarao/MAGNUS/magnus.html

As mentioned above, I also wonder if it's a combination of the small amount of attached spinning air causing some direct resistance to the air flow as well as causing seperation.

Jeffareid 17:20, 12 October 2007 (UTC)

Spinning Ball Potential Flow Simulation Image

Spinning Ball

I just uploaded a spinning ball potential flow simulation image that you might consider for inclusion in this article. Syguy 18:48, 23 October 2007 (UTC)

Incorrect Description

The effect of different velocities on the top and bottom surfaces actually acts AGAINST the Magnus effect. In the case of the picture on the page, the higher pressure is on the bottom. The boundary layer effect is greater than this effect however, thus the conclusion is, of course, accurate. —Preceding unsigned comment added by 209.202.5.230 (talk) 03:26, 27 March 2008 (UTC)

I'm unconvinced.

The flow converges around the bottom of the diagram. By the principle of volume conservation (which applies assuming the ball isn't going very fast relative to the speed of sound... and one thing's for sure, no-one can bowl that fast!) the flow must therefore be going faster. Hence, it has more kinetic energy.

That kinetic energy has to come from somewhere. It comes from a drop in fluid pressure.

Now, I'm not saying that the delayed boundary separation model is wrong... far from it! As Mtford states; The two effects work together; the delayed/aggrivated boundary layer separation causing the effect and being supported by the small contribution from the Bernoulli pressure differential.

I am disappointed that the article does not cover the main cause of the effect (outlined in the source linked by Jaffareid) though as I am not majoring in Aerodynamics I'll offer the edit to someone who is closer to the field. Spychotic (talk) —Preceding undated comment was added at 14:22, 13 October 2008 (UTC).

The main article is incorrect. Ignoring drag, Bernoulli's principle predicts a force OPPOSITE the Magnus force. The Magnus force is a result of drag - not lift. For a perfectly smooth ball Bernoulli's principle would dominate. For a rough ball, such as a tennis ball, the Magnus effect would dominate. As drag is proportional to velocity squared the forces on a spinning ball will be unbalanced. The main article needs some serious rewriting. Adair, R. K. (1994). The Physics of Baseball, 2nd ed. New York: HarperCollins, pp. 12, 22. —Preceding unsigned comment added by 192.231.40.3 (talk) 00:28, 4 September 2009 (UTC)

The real Coriolis Force

This looks to me like the real Coriolis force in action. David Tombe (talk) 18:25, 8 April 2009 (UTC)

On second thoughts, it's not a Coriolis force. It's a centrifugal force. Coriolis force is a windward effect in a vortex field that deflects an object at right angles. Coriolis force does no work. Centrifugal force is a right angle deflection due to transverse motion and it does do work.

The Magnus effect would therefore be closely related to these centrifugal effects,

(1) The force on a current carrying wire

(2) The force that keeps the planets up in their orbits.

(3) The force which causes an aeroplane to rise upwards. David Tombe (talk) 14:28, 9 April 2009 (UTC)

Magnus effect in northern and southern hemisphere

the coriolis/centrifugal force rotates to the right in the northern hemisphere and to the left in the southern hemisphere. So doesn't the rotation of the magnus effect differ in the northern and southern hemisphere aswell ?

if so, also change main picture in article to include both rotations —Preceding unsigned comment added by KVDP (talk • contribs) 11:42, 15 September 2009

KVDP, The rotation of the Earth causes Buys Ballot's law. But the Magnus effect is a local aerodynamical effect, in which case the rotation of the Earth would have no bearing on it. David Tombe (talk) 06:32, 16 September 2009 (UTC)

Hey guys! You have got it all wrong.

The Bernoulli principle is a simplification of Newtons 1 law of mechanics. Its absurd to think that moving air has lower pressure than not moving air. The pressure cannot change depending on from which air space you look at the phenomenon... The Bernoulli principle is useful when calculating aerodynamics but doesn´t explain the physics. When Bernoulli made his principle he deliberatly took the factor of mass out of the equation. He later got misinterpreted by a lot of people which led to this misconception.

The correct description, without knowing anything about math, is strictly concerning the shoveling effect of the spinning surface of the ball. The illustration in the article is wrong in all aspects.

On the side of the ball where the direction of the spinning air is coherent with the meeting air flow the turbulence is low. On the other side the collision of the spinning air and the meeting air flow produces vertical force that push the mass of the ball away. /Magnus H.

[1] —Preceding unsigned comment added by Hallin-m (talk • contribs) 12:40, 5 February 2010 (UTC)

Reference: Martin Ingelman-Sundberg —Preceding unsigned comment added by 95.209.176.228 (talk) 18:51, 3 February 2010 (UTC)

Principle

The current article was a mis-leading Bernoulli principle explanation of Magnus effect. It states that since the air speed is faster over the backwards moving surface than the forwards moving surface, then the pressure is less because of the faster moving air. However using the air as a frame of reference, the faster moving air occurs at the forward moving surface and the slower moving air at the backward moving surface. The issue here is that Beroulli doesn't relate pressure to relative speeds of air flow, but instead notes that as air accelerates from a higher pressure area to a lower pressure area, that during this acceleration the air increases speed as it's pressure decreases, and defines an equation that relates the speed to the pressure during this acceleration (an approximation that ignores issues like turbulence).

With a moving spinning ball, the air is accelerated (forwards) more by the forwards moving surface than the backwards moving surface. The higher acceleration coexists with a higher pressure. However the layer of air that actually spins with a ball is extremely thin, so it's unlikely that it would contribute much to the Magnus effect. The more likely explanation, is the difference in position (front to back) at where the attached flow separates from the surface of the ball. The flow detaches sooner on the forwards moving surface than it does on the backwards moving surface, resulting in a perpendicular diversion of flow (acceleration of air) towards the side of the ball that is spinning forwards, coexisting with an opposing perpendicular force from the air, creating the lift that curves the ball away from the side with the forwards moving surface.

Link to an archive of an article describing the detached flow. Note that the detached flows can occur on the front side of the sphere and the result will still be a normal Magnus effect:

magnus.html

Jeffareid (talk) 22:28, 15 February 2010 (UTC)

• Note - I updated the article to include both effects Jeffareid (talk) 22:57, 15 February 2010 (UTC)

Opposite effect with large, light objects?

On several occasions, I have noticed beach balls and plastic footballs to swerve away from their spin rather than towards it, as the Magnus effect proscribes, yet it is difficult to reconcile these observations without any counter forces mentioned in the phenomenon, nor any other effects being noted. Is there a different effect that produces the opposite motion when the object is large and light or when the velocity is low, or has something been missed in the article? AbrahamCat

I was just meditating on this again, and realised that Newton's Third Law of motion would be applicable where there is significant spin and surface area to produce a deflection, pushing air molecules towards the spin, and thus causing the object to react in the opposite motion. I suppose that this force depends on the surface area and angular velocity(spin) more than the forwards velocity of the object, thus when certain speeds are attained the force is cancelled out by the Magnus effect. It does however suggest that the Magnus effect equation will be inaccurate as the Newtonian forces will still be present. AbrahamCat 7-9-2010 —Preceding undated comment added 15:37, 7 September 2010 (UTC).

Bad explanation even has the direction of the force wrong

Look at the picture in the different-pressure explanation. It shows the ball accelerating from the lower pressure into the higher pressure. That should make anyone see that the explanation is all wrong. —Preceding unsigned comment added by 90.236.109.248 (talk) 18:04, 6 September 2010 (UTC)

Magnus effect and backspin

The illustration here contradicts the direction of rotation shown in Backspin. When folks here decide how Magnus Effect works, someone should check and fix Backspin. —Preceding unsigned comment added by 71.192.37.81 (talk) 15:07, 22 May 2011 (UTC)

used in Flettner Aeroplanes?

Is it really sensible to say the magnus effect is "used" in Flettner Aeroplanes when the Wikipedia article on such admits none has ever flown. I could just as well say the Magnus effect is "used" in my time travel machine which, incidentally, has never time traveled. — Preceding unsigned comment added by 69.149.77.212 (talk) 23:55, 8 January 2012 (UTC)

Poor Terminology

The following sentence is confusing: "This is because the induced velocity due to the boundary layer surrounding the spinning body is added to V on the forward-moving side, and subtracted from V on the backward-moving side."

The use of "forward-moving" side and "backward-moving" side is confusing. The "forward-moving" seems to me to be the side of the cylinder turning into the fluid not turning away from the fluid as it is used here. Forward moving implies that it is the side that is traveling in the same direction as the sphere or cylinder. Similar reasoning applies to the phrase "backward-moving" side.

Better phrasing might be: "The drag on the side of the sphere or cylinder turning into the fluid (into the direction the sphere or cylinder is traveling) slows the airflow..." — Preceding unsigned comment added by 24.5.15.244 (talk) 08:05, 4 March 2012 (UTC)

Figure

The direction of Magnus force drawn in the figure "Magnus_effect.svg" is incorrect. The force in the figure contains NEGATIVE drag force which accelerates the object against the flow. I have uploaded a figure which contains streamlines of the potential flow of Magnus Effect. くま兄やん (talk) 08:08, 18 July 2012 (UTC)

Formula for the force

Shouldn't the formula for the force from the Magnus effect make some reference to the angular velocity of the spinning object? It seems strange that it only contains the linear velocity. — Preceding unsigned comment added by 99.20.66.91 (talk) 12:30, 30 July 2012 (UTC)

I think the preceding comment refers to this formula

${F}={\frac {1}{2}}\rho v^{2}A\mathrm {C} _{L}$

and is a good question.

Rdurkacz (talk) 08:33, 11 January 2013 (UTC)

The Magnus force for a sphere is given as:

$\mathbf {F} \approx \left(\pi ^{2}r^{3}\rho \right){\boldsymbol {\omega }}\times \mathbf {v}$

"Slicing" the sphere into cylindrical strips I've calculated:

$\mathbf {F} =-{\frac {8\pi r^{3}\rho }{3}}{\boldsymbol {\omega }}\times \mathbf {v}$

Apart from the sign problem which could be a simple matter of convention (I took: positive rotation = counter-clockwise), I'm very intrigued by the inconsistent coefficients. Of course my calculation might be wrong but in any case I think a proof of the (correct!) sphere formula (or at least a reference thereof) should definitely be included!

Saxysellig (talk) 19:23, 18 March 2018 (UTC)

Review of main article

• The introductory material above should be incorporated into the article.
• The speculation below about the physics is obsolete with recent changes to the main article.
• The main article is not very good on who deserves credit for discovering the cause.
• It seems very unlikely that Newton could have had any valid insight into it, because he did not have a wind tunnel and he apparently connected it with his corpuscular theory of light.

I propose editing both the main article and the talk accordingly.--Rdurkacz (talk) 12:08, 18 February 2013 (UTC)

Does the video really show a valid example of the Magnus effect and the Bernoulli principle? It seems that the speed of rotation is too slow for any aerodynamic effects to be noticeable. On the other hand, the reel is suspended on the side and thus gravity simply creates a torque. 95.31.5.144 (talk) 00:04, 19 September 2017 (UTC)

Dropping basketball from height -- example of Magnus effect?

Video is here. Does it really work like this?--Tomwsulcer (talk) 10:16, 18 July 2015 (UTC) A better report here.--Tomwsulcer (talk) 10:24, 18 July 2015 (UTC)

Reynolds number relative to flow and cylinder

citing the article: "It is said[citation needed] that Magnus himself wrongly postulated a theoretical effect with laminar flow due to skin friction and viscosity as the cause of the Magnus effect."

I don't agree it was "wrongly postulated" ; indeed, the fluid speed relative to the cylinder make it that higher Reynolds number is achieved closer to the chord of the profile on the "lower" (counter-rotative, counter-flow) side.. where separation occurs and flow becomes turbulent. Beyond separation point, average medium speed relative to the cylinder is more or less zero, so pressure tends to be infinite (at least relative to the "upper" side). this would totally explain the Magnus effect.

In addition, it is known that turbulent flow can reduce drag and drag-induced oscillations (I can't find references right now, but many chimneys are fitted with devices to force flow separation) ; this can also explain the efficiency of Magnus-based lift devices relative to standard, "fixed-wing" profiles. — Preceding unsigned comment added by 2A02:1205:34E8:BC10:7CAE:34F4:8597:3968 (talk) 20:36, 27 October 2016 (UTC)

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Spinning missile (or artillery shell)

From article: «It is also an important factor in the study of the effects of spinning on guided missiles». Here the axis of spin is parallel to direction of movement. Will there be any Magnus effect? If so, why does it not cancel out? 80.212.60.189 (talk) 14:05, 27 June 2020 (UTC) Yes, there is a Magnus effect when the spinning object tends to deviate from its trajectory (if only because of its gyroscopic effect). See : Magnus Characteristics of Arbitrary Rotating Bodies, by I.D. Jacobson, AGARDograph No. 171, November 1973, (add https before the link). Bernard de Go Mars (talk) 16:18, 7 January 2023 (UTC)

References

2D liquid of hard disks

A 2D liquid of hard disks is made of molecules which interact with a hard disk potential. This means that they bounce on each other at a fixed distance between their centers. TD (talk) 06:06, 31 August 2020 (UTC)

Physics : G= (2 pi r)^2 s = 4 pi^2 r^2 omega

oméga = 2 pi r so G = (2.pi.r)^2 .s OR G = 4.pi^2.r^2 .omega i dont know which of both 2A02:8440:431C:2287:0:57:820E:4001 (talk) 02:38, 25 April 2021 (UTC)

Correct formula for ball

I’m trying to establish the formula for the Magnus effect on the trajectory of a spinning ball.

• The article (relying on [2]) says $F={\frac {4}{3}}\pi \rho r^{3}v\omega$.
• [3] is out by a factor of two with $F={\frac {8}{3}}\pi \rho r^{3}v\omega$ (note $\omega =2\pi s$).
• [4] suggests $F={\frac {1}{2+{\frac {v}{\omega r}}}}\pi r^{2}\rho {\frac {v^{2}}{2}}$.
• [5] suggests: ${\frac {1}{2}}\pi r^{2}\rho C_{M}v^{2}$ where $C_{M}=3.19*10^{-1}(1-e^{-2.48*10^{-3}\omega })$.

Which is right? Why is there such inconsistency? Bovlb (talk) 00:38, 24 July 2022 (UTC)

I have no expectation that the Magnus effect will display easy repeatability among different spheres or cylinders so I’m not surprised your sources have significant mismatch. The Magnus effect relies to some extent on the boundary layer so it will be influenced by surface finish - a tennis ball will behave differently to a cricket ball or golf ball etc. The equations you have quoted appear to have no way of accounting for surface characteristics. I suspect that if you want to find out about the performance of a particular sphere or cylinder you would be best advised to try to test it experimentally. Dolphin (t) 06:37, 24 July 2022 (UTC)

It's clear that surface characteristics will have an effect on drag torque (slowing the spin), but I'm still unclear on how they affect the Magnus effect. Is the suggestion that, depending on the friction of the surface, some of the delta V will not result in a delta P? Bovlb (talk) 16:04, 25 July 2022 (UTC)

It's also interesting to note that the first two formulae vary as $\omega v$ (assuming perpendicular), whereas the last two vary as $v^{2}$ with a more complex dependence on $\omega$. [6] says "The other force is the Magnus force, for a baseball it is parametrized as $F_{m}=S\omega \times v$, where S is independent of speed and is a constant. ... It is interesting to note in most literature this force is formulated as $F_{x}\sim \omega v^{2}$. However, the latter format simply reduces to the former." Bovlb (talk) 16:16, 25 July 2022 (UTC)