9. Vorticity (1 of 2)
Why Physics Stack Exchange recommends it
Physics Stack Exchange answerers link it when they need to show that vorticity is the curl of velocity, and that a flow can be rotational without visibly spinning or irrotational while curving.
Recommended by 3 people across 3 different months, 2014 to 2021.
What it is
Part 1 of a two-part lecture on vorticity from the classic National Committee for Fluid Mechanics Films series, produced about fifty years ago for undergraduate engineering and physics students. It uses lab demonstrations to explain vorticity as the curl of the velocity field and to contrast rotational and irrotational flow. This copy was uploaded by Barry Belmont, who did not make the original film.
What people said
Recommends philyd · 2014-11 · Physics Stack Exchange · on “Gravitational field has no curl? What about gas discs around stars, black holes, etc.?”
Is important to remember that curvature does not imply curl. Here is an analogy from fluid mechanics which deals with lack of vorticity (curl) in curved flow. This may seem counter-intuitive at the start, but hopefully you can see the similarities between the velocity field in the flow and the gravitational field. [this video]
Recommends tpg2114 · 2015-03 · Physics Stack Exchange · on “If the Earth's atmopsphere spins with the earth due to friction, why is there no horizontal spiralling drag?”
I'm not entirely clear on what you mean exactly, but I have a feeling you are unclear on the idea of a rotational and irrotational vortex [LINK] . Using your paint bucket analogy, there are two effects that create a rotational vortex. The spinning ball will drag fluid along with it. But because there is an outer wall to the bucket, viscosity requires that velocity to be zero. In a 2D sense, you are looking at a cylinder rotating within another. This is known as Taylor Couette flow [LINK] . Also, notice that the TC flow sets up cellular structures due to the rotation -- this is the same kind of effect you see in my answer [LINK] to your other question about bands forming in the atmosphere. Es
Recommends saketbyte · 2020-10 · Physics Stack Exchange · on “Solenoidal electric field”
For better understanding of an irrotational and rotational field I am attaching two video links about Vorticity(Vorticity is the curl of velocity of fluid flow) which cleared my concept to a good extent. The term here to emphasise is CURL and not rotation, using the word rotation gives the vague sense of it but curl actually is the more technically correct term. Vorticity part 1 [this video] Vorticity part 2 [LINK] Two points to understand crystal clear from link 1 are- a. A clear straight stream of water in a laminar flow is having rotationality(precisely Curl of Velocity is not zero), even though it appears to be just flowing in a straight line. b. A spinning tight vortex with a hole at the cen
Cites Steven Thomas Hatton · 2021-05 · Physics Stack Exchange · on “When is it true that "for a given velocity field, the curl represents a vector equal to twice the angular velocity vector"?”
I noticed that in one of those ancient videos the term "vorticity" was suggested to address my objection that nothing seems to actually be "rotating" in the case I presented. [this video]