16 January 2019, 08:33 AM
wtgInteresting example of rotational shear
(The gif shows the disc moving faster than it actually is)
quote:A huge ice disc has formed in the Presumpscot River in Westbrook, Portland television station CBS 13 reported.
The attention-grabbing formation is spinning counter clockwise and has served as a big raft for local birds, the TV station posted.
The discs “occur at bends in the river where the accelerating water creates a force called ‘rotational shear,’ which breaks off a chunk of ice and twists it around,” the Daily Mail once reported, when one of the circles was seen in Great Britain for what was believed to be the first time in 2009. “As the disc rotates, it grinds against surrounding ice, smoothing into a perfect circle.”
https://bangordailynews.com/20...-attracts-attention/