{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"b788922a5e01e7dcf75505782383d7aae80355a14b4519142b3d18cc12377877","created":"2026-10-03T07:18:03Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"0aac69b7f6c92ab4f23d71cb7a33d2f8a687307b86c4ed22172bd0259f6ac4a9","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"fluid.drop-impact.air-splash-mechanism","kind":"phenomenon","literature_status":"contested","n":"1","parents":[],"plain":"A drop hitting a smooth dry surface in air throws off a thin sheet that breaks into droplets, but in thin enough air the same impact does not splash at all. How the air produces the splash is not agreed.","posed_since":"2005","precise":"A low-viscosity drop of radius $R \\sim 0.1\\,\\mathrm{cm}$ hitting a smooth dry solid at speed $V$ of a few hundred cm/s splashes at 1 atm but not below a threshold gas pressure $P_{T}$ (Xu, Zhang, Nagel, PRL 2005). Identify the gas-mediated force that lifts the thin liquid sheet ejected near the contact line, and derive P_T(V, R, liquid viscosity, gas mean free path) together with the time and position of sheet ejection.","problem_ref":null,"references":"","settled_by":"Simultaneous measurement of gas-film thickness, sheet ejection time and $P_{T}$ across gases and liquid viscosities, matched by a theory without fitted parameters.","status_note":"Competing models invoke aerodynamic lift on the advancing sheet (Riboux and Gordillo 2014) and Kelvin-Helmholtz instability of a thin air film (arXiv:1509.01230); none is confirmed over the full parameter range.","title":"How does the surrounding gas cause an impacting drop to 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