Isnt the Thermodynamics of soap bubbles beautiful? The pressure inside an ideal (one surface) soap bubble can be derived from thermodynamic free energy considerations. At constant temperature and particle number, dT = dN = 0, the differential Helmholtz energy is given by dF\ = -PdV\ + \gamma dA where Pis the difference in pressure inside and outside of the bubble, and \gamma is the surface tension. In equilibrium, dF = 0, and so, PdV\ = \gamma dA. For a spherical bubble, the volume and surface area are given simply by V = \frac{4}{3}\pi R^3 \rightarrow dV \approx 4\pi R^2 dR, and A = 4\pi R^2 \rightarrow dA \approx 8\pi R dR. Substituting these relations into the previous expression, we find P = \frac{2}{R}\gamma, which is equivalent to the Young–Laplace equation when Rx = Ry. For real soap bubbles, the pressure is doubled due to the presence of two interfaces, one inside and one outside. Now that that is all clear watch the video :) :) Ana Yang Gazillion Bubble Show youtu.be/KMrvR836TFI
Posted on: Wed, 15 Oct 2014 13:48:38 +0000
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