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Tea leaf paradox
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<h2 id="explanation">Explanation</h2> <p>The stirring makes the water spin in the cup, causing a <a href="/facts/Centrifugal_force/CWgvMw6w">centrifugal force</a> outwards. Near the bottom however, the water is slowed by friction. Thus the centrifugal force is weaker near the bottom than higher up, leading to a secondary circular (helical) flow that goes outwards at the top, down along the outer edge, inwards along the bottom, bringing the leaves to the center, and then up again.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <h2 id="applications">Applications</h2> <p>The phenomenon has been used to develop a new technique to separate <a href="/facts/Red_blood_cell/Kggpq8Jh">red blood cells</a> from <a href="/facts/Blood_plasma/oHuwwugG">blood plasma</a>,<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> to understand atmospheric pressure systems,<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> and in the process of <a href="/facts/Brewing/aKCgJVyJ">brewing</a> <a href="/facts/Beer/t7qAGDfj">beer</a> to separate out coagulated <a href="/facts/Trub_(brewing)/4VLaFfKM">trub</a> in the whirlpool.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Baer%E2%80%93Babinet_law/52gRcRh5">Baer–Babinet law</a>, also known as Baer's law – Theory on the formation of rivers due to Earth's rotation</li> <li><a href="/facts/Ekman_layer/d0j2UE43">Ekman layer</a> – Force equilibrium layer in a liquid</li> <li><a href="/facts/Secondary_flow/0Hhz4cTJ">Secondary flow</a> – Relatively minor flow superimposed on the primary flow by inviscid assumptions</li></ul> <h2 id="external-links">External links</h2> <ul><li>Highfield, Roger (14 January 2008). <a href="https://archive.today/20121209094124/http://www.telegraph.co.uk/scienceandtechnology/science/sciencenews/3291786/Dr-Roger%27s-Home-Experiments.html">"Dr Roger's Home Experiments"</a>. <a href="/facts/The_Daily_Telegraph/aHa5nNw5">The Daily Telegraph</a>. Archived from <a href="https://www.telegraph.co.uk/scienceandtechnology/science/sciencenews/3291786/Dr-Roger%27s-Home-Experiments.html">the original</a> on 9 December 2012. Retrieved 2008-12-28.</li> <li>Sethi, Ricky J. (September 30, 1997). <a href="http://www.madsci.org/posts/archives/1997-12/875655758.Ph.r.html">"Why do particles move towards the center of the cup instead of outer rim?"</a>. <a href="/facts/MadSci_Network/bH2f5Wqf">MadSci Network</a>. Retrieved 2008-12-29.</li> <li>Booker, John R. <a href="http://earthweb.ess.washington.edu/roe/ESS514_notes/ch5.pdf">"Student Notes - Physics of Fluids - ESS 514/414"</a> (PDF). Department of Earth and Space Sciences, University of Washington. ch. 5.8 p. 48. Retrieved 2008-12-29. See also figure 25 in <a href="http://earthweb.ess.washington.edu/roe/ESS514_notes/figures.pdf">figures.pdf</a></li> <li>Stubley, Gordon D. (May 31, 2001). <a href="https://web.archive.org/web/20090206000717/http://ansys.com/solutions/documents/mystery.pdf">"Mysteries of Engineering Fluid Mechanics"</a> (PDF). Mechanical Engineering Department, University of Waterloo. Archived from <a href="http://www.ansys.com/solutions/documents/mystery.pdf">the original</a> (PDF) on February 6, 2009. Retrieved 2008-12-29.</li> <li>Einstein's 1926 article online and analyzed on <i><a href="https://www.bibnum.education.fr/sciences-de-la-terre/meteorologie/albert-einstein-et-la-tasse-de-de-mme-schrodinger">BibNum</a></i> (click 'Télécharger' for English) (unsecure link).</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>James Thomson, On the grand currents of atmospheric circulation (1857). Collected Papers in Physics and Engineering, Cambridge Univ., 1912, 144–148. DjVu file. <a href="https://vk.com/wall-102183983_116" target="_blank">https://vk.com/wall-102183983_116</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Boussinesq J. (1868). "Mémoire sur l'influence des frottements dans les mouvements réguliers des fluides" (PDF). Journal de mathématiques pures et appliquées. 2e Série (in French). 13: 377–424. Archived from the original (PDF) on March 17, 2022. <a href="/wiki/Joseph_Valentin_Boussinesq" target="_blank">/wiki/Joseph_Valentin_Boussinesq</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>His results are cited in: Joukovsky N. E. (1914). "On the motion of water at a turn of a river". Matematicheskii Sbornik. 29. Reprinted in: Collected works. Vol. 4. Moscow; Leningrad. 1937. pp. 193–216, 231–233 (abstract in English).{{cite book}}: CS1 maint: location missing publisher (link) <a href="/wiki/Nikolay_Yegorovich_Zhukovsky" target="_blank">/wiki/Nikolay_Yegorovich_Zhukovsky</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Bowker, Kent A. (1988). "Albert Einstein and Meandering Rivers". Earth Science History. 1 (1): 45. Bibcode:1988ESHis...7...45B. doi:10.17704/eshi.7.1.yk72n55q84qxu5n6. Retrieved 2008-12-28. <a href="http://www.searchanddiscovery.net/documents/Einstein/albert.htm" target="_blank">http://www.searchanddiscovery.net/documents/Einstein/albert.htm</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Einstein, Albert (March 1926). "Die Ursache der Mäanderbildung der Flußläufe und des sogenannten Baerschen Gesetzes". Die Naturwissenschaften (in German). 14 (11). Berlin / Heidelberg: Springer: 223–224. Bibcode:1926NW.....14..223E. doi:10.1007/BF01510300. S2CID 39899416. English translation: The Cause of the Formation of Meanders in the Courses of Rivers and of the So-Called Baer's Law, accessed 2017-12-12. <a href="/wiki/Die_Naturwissenschaften" target="_blank">/wiki/Die_Naturwissenschaften</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Einstein, Albert (March 1926). "Die Ursache der Mäanderbildung der Flußläufe und des sogenannten Baerschen Gesetzes". Die Naturwissenschaften (in German). 14 (11). Berlin / Heidelberg: Springer: 223–224. Bibcode:1926NW.....14..223E. doi:10.1007/BF01510300. S2CID 39899416. English translation: The Cause of the Formation of Meanders in the Courses of Rivers and of the So-Called Baer's Law, accessed 2017-12-12. <a href="/wiki/Die_Naturwissenschaften" target="_blank">/wiki/Die_Naturwissenschaften</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Arifin, Dian R.; Leslie Y. Yeo; James R. Friend (20 December 2006). "Microfluidic blood plasma separation via bulk electrohydrodynamic flows". Biomicrofluidics. 1 (1). American Institute of Physics: 014103 (CID). doi:10.1063/1.2409629. PMC 2709949. PMID 19693352. Archived from the original on 9 December 2012. Retrieved 2008-12-28. "Einstein's Tea Leaves Inspire New Blood Separation Technique". Science Daily (Press release). January 17, 2007. <a href="https://archive.today/20121209001530/http://link.aip.org/link/?BIOMGB/1/14103/1" target="_blank">https://archive.today/20121209001530/http://link.aip.org/link/?BIOMGB/1/14103/1</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Pincock, Stephen (17 January 2007). "Einstein's tea-leaves inspire new gadget". ABC Online. Retrieved 2008-12-28. <a href="http://www.abc.net.au/science/news/stories/2007/1828408.htm" target="_blank">http://www.abc.net.au/science/news/stories/2007/1828408.htm</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Tandon, Amit; Marshall, John (2010). "Einstein's Tea Leaves and Pressure Systems in the Atmosphere". The Physics Teacher. 48 (5): 292–295. Bibcode:2010PhTea..48..292T. doi:10.1119/1.3393055. hdl:1721.1/118473. <a href="https://doi.org/10.1119%2F1.3393055" target="_blank">https://doi.org/10.1119%2F1.3393055</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Bamforth, Charles W. (2003). Beer: tap into the art and science of brewing (2nd ed.). Oxford University Press. p. 56. ISBN 978-0-19-515479-5. <a href="978-0-19-515479-5" target="_blank">978-0-19-515479-5</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> </ol>