Summary and Concept Map

SUMMARY. The interatomic force between the atoms of an element, and the intermolecular force between the molecules of a compound, are the microscopic forces underlying every macroscopic property covered in this unit. Hooke's law: within the elastic limit, stress is directly proportional to strain. Stress is force per unit area, $F/A$; tensile or compressive stress together are called longitudinal stress. Longitudinal strain is $\Delta L/L$. Within the elastic limit, the ratio of longitudinal stress to longitudinal strain is Young's modulus; the ratio of volume stress to volume strain is bulk modulus; the ratio of shear stress to shear strain is rigidity modulus. Poisson's ratio equals lateral strain over longitudinal strain. The elastic potential energy stored per unit volume of a stretched wire is $U=\tfrac12\times\text{stress}\times\text{strain}=\tfrac12 Y(\text{strain})^2$. Pressure is defined as force acting per unit area on a surface. The total pressure at depth h below a liquid surface is $P=P_a+\rho gh$, where $P_a=1.013\times10^5$ Pa is atmospheric pressure. Pascal's law states pressure in a fluid at rest is the same at all points at the same height. The law of floatation states a body floats in a liquid if the weight of liquid displaced by its immersed part equals (or exceeds) the weight of the body. The coefficient of viscosity is the viscous force acting tangentially per unit area of a liquid layer with unit velocity gradient perpendicular to the flow direction. Streamlined flow is when each liquid particle passing a point follows the same path with the same velocity as its predecessor; once the critical velocity is exceeded, the flow becomes turbulent. Reynold's number decides whether flow through a cylindrical pipe is streamlined or turbulent. Stoke's formula is $F=6\pi\eta a v$ for the viscous force on a sphere of radius a moving with terminal velocity v. Surface tension is the force of tension acting on a unit length of an imaginary line on the free liquid surface, perpendicular to the line and parallel to the surface. The angle of contact is the angle between the tangents drawn at the point of contact to the liquid surface and the solid surface, measured inside the liquid. Flow is steady if the velocity of every particle passing a given point remains constant with time. The equation of continuity, $a_1v_1=a_2v_2$, follows from conservation of mass in fluid flow. Bernoulli's theorem states that the sum of pressure energy, kinetic energy and potential energy per unit mass of an incompressible, non-viscous fluid in streamlined flow remains constant: $P/\rho+v^2/2+gh=\text{constant}$. CONCEPT MAP. The unit's ideas branch from 'Properties of Matter' into two halves. Under SOLID: e …