PHY1039 Properties of Matter State Variables 9 February, 2012 Lecture 2

Extrinsic State Variables A F Pressure, P F Tension, F L Positive P is pressing inward. P can also be a negative quantity. Surface Tension,  A F Membrane At mechanical equilibrium, the force acting along the edge balances . Positive P is pulling outward.

Hydrostatic Pressure on a Solid High Pressure Diamond Anvil CellPiston The surrounding fluid ensures that the force per unit area is constant across the entire surface of the solid. Used by Prof. Alf Adams’ group at Surrey when studying electrical and optical properties of semiconductors for applications in lasers. Earth’s atmosphere exerts a hydrostatic pressure of about 1.02 x 10 5 Pa (not a constant) Figures from “Understanding Properties of Matter” by M. de Podesta

Meniscus Measuring Surface Tension of Liquids Wilhelmy plate method Vector  represents surface tension A force is required to distort the meniscus (up or down) – pulling against molecular attractive forces /hesla/metody.vyvazovani_desky.html

Surface Tensions of Liquids Table from “Understanding Properties of Matter” by M. de Podesta Image from: bjects/602/616516/Chapter_10.html

Surface Tension is Temperature Dependent Water K =  C At higher temperatures, molecules are slightly farther apart, and so their attraction to each other is weaker – hence  is lower.  usually does not vary much with the area of a surface of liquid. Why? Figures from “Understanding Properties of Matter” by M. de Podesta