Why Don’t Sheep Shrink In The Rain?

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Getting wet isn’t REALLY what makes wool shrink; it merely exacerbates the friction between the wool fibers, which is stronger in one direction than another, so when agitated in the washer or dryer, they migrate in relation to each other in a process called “felting.”
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To learn more about this topic, start your googling with these keywords:
Fiber: a threadlike structure forming part of the muscular, nervous, connective, or other tissue in the human or animal body
Felting: the process by which wool or another textile can be agitated, often along with moisture or heat, to cause the fibers to migrate amongst themselves and mat together into a dense smooth surface
Ratchet: a device consisting of a bar or wheel with a set of angled teeth that allow motion in one direction only
Wool: soft curly or wavy hair forming the coat of a sheep or similar animal, especially when cut off the animal & prepared for use in making cloth or yarn
Mammal: a warm-blooded, bony, & hairy/furry animal, the females of which give birth to live young and nurse them with milk

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Credits (and Twitter handles):
Script Writer: Emily Elert (@eelert)
Script Editor: Alex Reich (@alexhreich)
Video Illustrator: Qingyang (@QCVisual)
Video Director: Henry Reich (@MinutePhysics)
Video Narrator: Kate Yoshida (@KateYoshida)
With Contributions From: Ever Salazar, Peter Reich, David Goldenberg
Music by: Nathaniel Schroeder:

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If you liked this week’s video, we think you might also like:
Is it Better to Walk or Run in the Rain?

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References:

Gupta, N. P., Agarwal, R., & Pant, S. (2009). Factors affecting felting of wool: An overview. Colourage, 56(1).

Johnson, N. A., & Russell, I. (Eds.). (2008). Advances in wool technology. Elsevier.

Makinson, K. R. (1972). The Role of the Scales of Wool Fibers in Felting and in Shrinkproofing. Wool Sci. Rev, (42), 2-16.

Makinson, K. R. (1979). Shrinkproofing of wool (Vol. 8). M. Dekker. Chicago.

Menkart, J., & Speakman, J. B. (1945). Scaliness of Wool Fibres. Nature, 156, 143-143.

van der Vegt, A. K. (1955). A study on the mechanism of wool felting. Excelsior.