User talk:Helpful-Concrete

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Hello Helpful-Concrete, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay.

At Wikipedia, new Users do not automatically receive a welcome; not even a machine-generated welcome. Welcome messages come from other Users. They are personal and genuine. They contain an offer of assistance if such assistance is ever desired.

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I hope you enjoy editing here and being a Wikipedian! If you need help, check out Wikipedia:Questions, ask me on my talk page, or place {{helpme}} on your talk page and ask your question there. Again, welcome! Dolphin (t) 13:17, 5 September 2024 (UTC)[reply]

Magnus effect

Hi H-C. on 4 September you deleted an infographic at Magnus effect - see your diff. Your edit summary included Faster relative motion results in lower pressure ...

In the past we have seen Users who believe the Magnus effect is due to the difference in relative speed between the oncoming air and the surface of the spinning ball, leading to lower pressure on one side of the ball, and higher pressure on the other. That is definitely incorrect.

If we are using the reference frame of the spinning ball, the speed of the ball is zero and the oncoming air has a significant speed towards the stationary ball. The lower pressure is in the air that is moving faster in this reference frame; and the higher pressure is in the air that is moving slower. Some of the air is moving faster because it is accelerated by viscous shear forces at the surface of the ball, as these shear forces try to drag the air around with the surface of the ball. Some of the air is moving slower because it is decelerated by the viscous shear forces at the surface of the ball, as these shear forces try to slow the speed of the oncoming air.

If a golf ball has back spin the ball remains airborne longer than if it has no spin. If the "relative speed" explanation was correct, a back spinning golf ball would remain airborne for a shorter time and travel a shorter distance.

Magnus effect is an effect associated with the viscosity of the air. If the air was inviscid there would be no viscous shear forces so no Magnus effect even though the relative speeds of the air and the surface of the ball would still be different on the two sides.

You removed one infographic but left the other. Both infographics appear to me to show the ball spinning anti-clockwise and curving to the left. Please have a close look at your edit, and the two infographics. I think you have removed the infographic in error. Dolphin (t) 13:40, 5 September 2024 (UTC)[reply]