Ch 12 - Kinetic Theory11th Physics

Historical Context

• Vaiseshika School: Founded by Kanada in the 6th century B.C., this school detailed the atomic picture of matter long before modern science.
• Paramanu: The Sanskrit word for the smallest, indivisible ultimate particle of matter.

Note: In ancient Greece, Democritus also proposed the 'atom' (meaning indivisible) in the 4th century B.C., while John Dalton is credited with the modern scientific atomic theory.

Definition

Brownian Motion is the continuous, random, zig-zag macroscopic movement of microscopic particles (like pollen grains) suspended in a fluid (liquid or gas).

Evidence for Kinetic Theory

• It physically proves that the molecules of the fluid are in constant, chaotic, thermal motion.
• The random macroscopic movement of the suspended particles is caused by the unequal, unbalanced microscopic collisions from the invisible fluid molecules striking them from all sides.

Variables & Units:

• P = Pressure (Pa)
• V = Volume (m³)
• N = Total number of gas molecules
• k_B = Boltzmann constant ($1.38 \times 10^{-23}$ J/K)
• T = Absolute temperature (K)

Conditions/Notes:

• The Boltzmann constant relates macroscopic thermodynamic temperature to microscopic energy.
• This can also be written in terms of number density ($n = N/V$) as $P = n k_B T$.