User talk:Tedkurtz

Welcome to Wikipedia. We appreciate your contributions, but in one of your recent edits, it appears that you have added original research, which is against Wikipedia's policies. Original research refers to material—such as facts, allegations, ideas, and personal experiences—for which no reliable, published sources exist; it also encompasses combining published sources in a way to imply something that none of them explicitly say. Please be prepared to cite a reliable source for all of your contributions. Thank you. Materialscientist (talk) 02:52, 27 September 2018 (UTC)

Magnus effect (again)
Hi Ted! Firstly, please don't go adding discussion to the main article - that's what talk pages are for. Secondly, please think through your example again. If a baseball is thrown with topspin, the top of the ball is moving through the air faster than the bottom, because the rotation adds to the forward movement at the top and subtracts from it at the bottom. With backspin, the opposite is true. The higher the airspeed, the lower the pressure, because of the Bernoulli effect. So with backspin the bottom is faster, and has lower pressure, and the ball dips down. Got it now? Philip Trueman (talk) 15:46, 19 October 2018 (UTC)


 * I must disagree with you. You haven’t completed your explanation. If you had completed it you would have noticed that you are at variance with what is written in Magnus effect. You have correctly stated that topspin causes the top of the ball to move with faster airspeed than the bottom, but without clarifying what you intend by “airspeed”. You have also quoted Bernoulli as “higher airspeed, lower pressure” (but remember that Bernoulli applies along a streamline, so your application of Bernoulli is most likely done incorrectly.) You haven’t reached any conclusion regarding the effect of topspin, but if you had done so, it would be “topspin causes lower pressure on the top of the ball, and higher pressure on the bottom, and therefore topspin imparts an upward force.” Our article states the opposite — it says topspin imparts a downward force (and backspin imparts an upward force.)


 * The cause of the mismatch is that your explanation here for Ted Kurtz omits a vital element. The less-than-perfectly-smooth surface of the ball combines with the viscosity of the air, causing the spinning ball to try to drag the air around with it in a spinning motion or vortex. In the case of a top-spinning ball, the air near the top of the ball has lower speed because the movement of the top of the ball is slowing the air (and hence a higher pressure by Bernoulli.) The air near the bottom of the ball has higher speed because the movement of the bottom of the ball is accelerating the air, and hence a lower pressure. Consequently a top-spinning ball experiences a downward force as stated in our article.


 * In an ideal fluid without viscosity a spinning ball would not drag the air around with it in a spinning motion, or vortex; if it has topspin and is moving at speed through the ideal fluid it would not impart any lateral force, even though its top would have a higher airspeed (your word) than the bottom. Magnus effect is a consequence of viscosity but your explanation does not acknowledge the role played by viscosity (a very common misunderstanding of Magnus effect.) That is why, if you had reached a conclusion, it would have been at variance with what is stated in the article. Dolphin ( t ) 00:01, 24 October 2018 (UTC)


 * Hmm. Thank you. I saw no need to get to the conclusion of 'topspin', because I wanted to get quickly to the conclusion for Ted's 'curveball' example. And you lost me with "the air near the top of the ball has lower speed because the movement of the top of the ball is slowing the air" - in what reference frame?  I think that's a discussion for somewhere else. You have at any rate convinced me that there's more to this than I thought, and also that there is scope for improving the article. Philip Trueman (talk) 02:50, 24 October 2018 (UTC)

Thank you. I'm sorry. I have never edited WikipediA before and did not know what the procedure for editing was. I will try to follow the proper procedures in the future. I've recently become a baseball fan and last night watched the Red Sox win the American League Pennant. A baseball curve ball is thrown with back spin and causes the ball to curve sharply downwards. In golf, a driver club imparts top spin to the ball which generates lift results in increasing the distance the ball flies. You can confirm this, if you wish, by talking to baseball or golf enthusiasts. This behavior is the opposite of what would be predicted by the Magnus Effect. I believe I understand the physics involved, but that is not the point I'm trying to make here. I'm just trying to point out that, as baseball and golf enthusiasts could confirm, the Magnus Effect does not predict what happens.

It's not really relevant, but I have a PhD in Mechanical Engineering from MIT and taught Applied Mechanics there for a while. In approximately 1965 I was a consultant for Titlist and developed a wind tunnel which they used for measuring the aerodynamic force on golf balls. Unfortunately for me, they did not want their competitors to know about that and I was not able to publish the results.

Best regards, Ted