lesson
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When you inflate a soccer ball, it stays firm for days even though it is filled with invisible air. What keeps that ball pushed outward from the inside without ever getting tired?
The answer lies in trillions of microscopic particles colliding against the ball's inner wall at hundreds of miles per hour.
The Microscopic Model of Gases
In the mid-1800s, physicists Rudolf Clausius, James Clerk Maxwell, and Ludwig Boltzmann developed the Kinetic Molecular Theory (KMT) to explain macroscopic gas properties like pressure and temperature using particle motion.
KMT relies on five core postulates that describe the behavior of an ideal gas — a theoretical gas whose particles follow these rules perfectly under all conditions.
Postulates 1 & 2: Volume and Motion
Postulate 1: A gas consists of tiny particles separated by vast distances, meaning the actual particle volume is negligible compared to the total volume of empty space.
Postulate 2: Gas particles are in constant, rapid, random straight-line motion until they collide with each other or the container walls.
📊A clean 2D interactive container diagram showing 10 small circular gas particles (bright blue dots) moving at straight angles inside a rounded container with light gray walls (#e6e6e6). Dotted trail lines show straight paths bouncing off walls. A callout badge highlights '99.9% Empty Space' and another shows 'Negligible Particle Volume'. High contrast, clean cards (#ffffff) on light gray background (#f8f9fa), dark text (#1e2945). Responsive to 350px width.
What happens when these constantly moving particles slam into one another?
Postulates 3 & 4: Forces and Collisions
Postulate 3: There are no attractive or repulsive intermolecular forces between gas particles; they neither pull toward nor repel one another as they pass.
Postulate 4: Collisions between particles or with container walls are elastic collisions, meaning total kinetic energy is perfectly conserved and no energy is lost as heat.