PHY1039

Properties of MatterState Variables

9 February, 2012

Lecture 2

Extrinsic State Variables

A

P=

F

Pressure, P

F

Tension, F

L

Positive P is pressing inward.P can also be a negative quantity.

Surface Tension, G

A F

Membrane

Γ=F  2 ℓ

At mechanical equilibrium, the force acting along the edge balances G.

Positive P is pulling outward.

ℓ

Hydrostatic Pressure on a SolidHigh 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 105 Pa (not a constant)

Figures from “Understanding Properties of Matter” by M. de Podesta

Meniscus

Measuring Surface Tension of Liquids

Wilhelmy plate method

http://fiesta.bren.ucsb.edu/~vbroje/oil_spill_research_laboratory.htm

Vector g represents surface tension

A force is required to distort the meniscus (up or down) – pulling against molecular attractive forces.

http://vydavatelstvi.vscht.cz/knihy/uid_es-001/hesla/metody.vyvazovani_desky.html

Surface Tensions of Liquids

Table from “Understanding Properties of Matter” by M. de Podesta

Image from: http://wps.prenhall.com/wps/media/objects/602/616516/Chapter_10.html

Surface Tension is Temperature Dependent

WaterK = C + 273.15

At higher temperatures, molecules are slightly farther apart, and so their attraction to each other is weaker – hence G is lower.

G usually does not vary much with the area of a surface of liquid. Why?

Figures from “Understanding Properties of Matter” by M. de Podesta