JEFA ƘWALLO A CIKIN RUWA: MATSEWAR ISKA TA BIYU CE KE YANKE KO ZAI DAWO

Lokacin da wani abu mai ƙarfi ya faɗa cikin ruwa, yana jan iska tare da shi, yana buɗe rami (cavity) a bayansa kuma yana jin ƙarfi kwatsam da ke juya hanyarsa. Wannan “matsalar shigar ruwa” (water-entry problem) tana da muhimmanci ga saukar jiragen sama na ruwa (seaplanes), harsasai (projectiles) da robots na ƙarƙashin ruwa, kuma tana da kwatankwacinta a cikin halitta. Nazarinta ya fara ne da hotunan Worthington masu sauri na ƙwallo yana faɗawa ruwa, a 1883.

An san abubuwa da yawa game da lokutan farko. Ramin iskar da ke bayan ƙwallo mai nutsewa yana miƙewa, sannan ya matse ya rabu (pinches off) — matsewar farko (primary pinch-off) — yana barin aljihun iska manne da ƙwallon. Abin da ke faruwa bayan haka ba a bincika shi sosai ba, musamman ga ƙwallaye masu sauƙi. Prasanna Kumar Billa da Pallab Sinha Mahapatra, a Indian Institute of Technology Madras, da Cameron Tropea, a IIT Madras da Technical University of Darmstadt, sun bi sauran labarin.

Ƙwallaye, shafe-shafe da kyamarori masu sauri

Ƙungiyar ta jefa ƙwallaye na milimita 4, 6 da 10, masu yawa (density) sau 1.12 zuwa 7.92 na na ruwa, cikin tanki mai zurfin santimita 40. Wani bututun tsotsa (vacuum pipette) ya sake su daga tsayi tsakanin milimita 49 da 633, ta yadda suka bugi saman ruwa da saurin mita 0.89 zuwa 3.52 a daƙiƙa ɗaya. Kyamarori masu sauri sun ɗauki bidiyo a hotuna 1,000 da 2,000 a daƙiƙa ɗaya, kuma an maimaita kowane yanayi aƙalla sau uku.

Fuskokin sun zo iri biyu. Ƙwallaye masu ƙin ruwa (hydrophobic) suna korar ruwa, da kusurwar taɓawa (contact angle) ta kusan digiri 100. Ƙwallaye masu tsananin ƙin ruwa (superhydrophobic), da aka shafa musu feshin hana ruwa na kasuwa, suna kaiwa kusan digiri 155; sama da digiri 150, ana ɗaukar fuska a matsayin mai tsananin ƙin ruwa.

Shigar ruwa na ƙwallaye masu ƙin ruwa (sama) da masu tsananin ƙin ruwa (ƙasa). (b) Ƙwallo mai ƙin ruwa na milimita 4 yana rasa iskarsa kuma yana ci gaba da nutsewa; (d) ƙwallo mai tsananin ƙin ruwa na milimita 4 yana riƙe da layin iska kuma yana dawowa sama. — Hoto na 2, Billa, Tropea & Sinha Mahapatra (2026), arXiv:2610.41942.

Bambancin yana bayyana nan take. A bayan ƙwallo mai ƙin ruwa ramin yana da kaushi, kuma ruwa yana jiƙa ƙwallon har zuwa tsakiyarsa (equator). Ƙwallo mai tsananin ƙin ruwa yana lulluɓe gaba ɗaya da iska, kuma ramin sa yana da bango masu santsi.

Ƙofa mai hanya ɗaya

Daga bidiyon, ƙungiyar ta bi matsayin kowane ƙwallo, saurinsa da hanzarinsa (acceleration), kuma ta auna girman ƙwallo tare da iskar da ke manne da shi. Bayan matsewar farko, hanzari ƙanana ne kuma daidaiton ƙarfi yana da sauƙi: nauyi yana ja zuwa ƙasa, ƙarfin tunkuɗa sama daga dukkan girman ruwan da aka kawar yana turawa sama, jan ruwa (drag) yana hana motsi.

Don haka ƙa’idar dawowa ita ce ƙarfin tunkuɗa sama (buoyancy) kawai: ƙwallon yana komawa saman ruwa ne kawai idan girman da yake kawarwa, har da iskarsa, ya fi girmansa sau rabon yawansa (density ratio). Ƙwallo na milimita 6 da ya riƙe kawarwa sau 1.42 na girmansa, da rabon yawa 1.12, ya juya ya tashi. Ƙwallo na milimita 10 da iskarsa ta matse a karo na biyu ya rage da 1.02 — bai isa ba — kuma ya ci gaba da nutsewa.

Babban abin lura shi ne ƙofa mai hanya ɗaya: duk lokacin da ramin da ke manne ya matse a karo na biyu, ƙwallon bai taɓa dawowa ba. Babu ƙwallo da yawansa ya kai aƙalla sau 3.26 na na ruwa da ya sake tashi, kuma babu wanda kusurwar taɓawarsa ke ƙasa da digiri 97.

Girma, sauri da sa’a

Jiƙuwa (wettability) tana taimakawa, amma ba ita kaɗai ke yanke hukunci ba. A cikin ƙwallaye mafi sauƙi masu tsananin ƙin ruwa, kowane ƙwallo na milimita 4 ya tashi, kowane na milimita 10 ya nutse, kuma na milimita 6 sun yi duka biyun daga maimaitawa ɗaya zuwa na gaba. Bugawa mafi sauri na iya haifar da matsewa ta biyu su aika har ƙwallaye masu ƙin ruwa zuwa ƙasa. Kuma a yanayi biyu, ƙwallaye masu ƙin ruwa sun tashi a gwaji biyu cikin huɗu.

Zurfi bisa lokaci ga ƙwallaye mafi sauƙi masu tsananin ƙin ruwa, gwaji uku kowanne: ƙwallaye na milimita 4 suna dawowa (a, b), na milimita 10 suna ci gaba da nutsewa (e, f), kuma na milimita 6 na iya yin ko wanne (c, d). — Hoto na 6, Billa, Tropea & Sinha Mahapatra (2026), arXiv:2610.41942.

Kallon wuya

Me ke yanke matsewa ta biyu? Ƙungiyar ta zuƙo kan wuyan ramin da ke manne, wurin da ya fi ƙunci. A ƙwallaye na milimita 4, wuyan yana farawa a faɗi, a 65 zuwa 97% na radius ɗin ƙwallon, sannan ya ƙunce, yayin da layin da ruwa, iska da ƙwallo ke haɗuwa yake ƙaura a saman ƙwallon.

Kwatanta ƙarfin tunkuɗa sama na iskar da ke kame da nauyin ƙwallon da ƙarfin fatar ruwa (surface tension) da ke riƙe wuyan yana ba da radius na ma’auni. Ramukan da suka tsira da waɗanda suka karye galibi sun faɗa a ɓangarori masu gaba da juna na wannan radius. Amma marubutan suna taka-tsantsan: wuyan da ke rufewa zai ƙetare kowace iyaka a ƙarshe, don haka an zana wannan rabuwar ne bayan abin ya faru kuma ba ta hasashen matsewa. Hasashenta zai buƙaci matsin iskar da siffar wuyan, haɗe da ƙwallon da ke motsi, waɗanda bidiyon ba sa nunawa dalla-dalla.

Sakamako tabbatacce shi ne jerin sanadi da sakamako: yadda wuyan ke sauyawa yana ƙayyade yawan iskar da ke ci gaba da manne, kuma wannan iskar ce ke yanke, ta hanyar ƙarfin tunkuɗa sama, inda ƙwallon zai nufa a ƙarshe. Jiƙuwa tana da muhimmanci ta hanyar wannan iskar — ba ita kaɗai ba.