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Question Number 208789 by Tawa11 last updated on 23/Jun/24

$$\mathrm{Why}\mathrm{is}\mathrm{surface}\mathrm{tension}\mathrm{formula}\mathrm{divided}\mathrm{by}2\mathrm{L}$$$$\mathrm{that}\mathrm{is},\mathrm{surface}\mathrm{tension}=\frac{\mathrm{F}}{2\mathrm{L}}$$$$\mathrm{why}\mathrm{divided}\mathrm{by}2\mathrm{L}.$$$$\mathrm{Where}\mathrm{did}\mathrm{the}2\mathrm{come}\mathrm{from}?$$$$$$$$\mathrm{Example}.$$$$\mathrm{Calculate}\mathrm{the}\mathrm{force}\mathrm{required}\mathrm{to}\mathrm{lift}\mathrm{a}\mathrm{needle}$$$$4\mathrm{cm}\mathrm{long}\mathrm{off}\mathrm{the}\mathrm{surface}\mathrm{of}\mathrm{water},\mathrm{if}\mathrm{surface}$$$$\mathrm{tension}\mathrm{of}\mathrm{water}\mathrm{is}7.3\times {10}^{-4}{\mathrm{Nm}}^{-1}$$$$$$$$\mathrm{Why}\mathrm{is}\mathrm{the}\mathrm{formula}\mathrm{surface}\mathrm{tension}=\frac{\mathrm{F}}{2\mathrm{L}}$$$$\mathrm{why}\mathrm{not}\mathrm{surface}\mathrm{tension}=\frac{\mathrm{F}}{\mathrm{L}}$$

Commented by mr W last updated on 23/Jun/24

$$surface=perimeter$$$$ifthewidthofyourhandisL,and$$$$youputyourhandintowater,$$$$yourhandhastwosides,both$$$$sidescantactwater.thisis$$$$wherethe2comesfrom.$$$$tobeexact,itis\frac{F}{2L+2D},butsince$$$$thethicknessDisverysmall$$$$comparedwithitslengthL,sowe$$$$cansay\frac{F}{2L+2B}\approx \frac{F}{2L}$$

Commented by mr W last updated on 23/Jun/24

Commented by Tawa11 last updated on 23/Jun/24

$$\mathrm{Thanks}\mathrm{sir}.$$$$\mathrm{I}\mathrm{appreciate}.$$

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