IGCSE 0625 · THERMAL · 2.1

Kinetic particle model

How the particle model explains solids, liquids, and gases, Brownian motion, and gas pressure. It builds on density, kinetic energy, and pressure from Topic 1, and leads into the thermal properties and energy transfer that follow.

TOPIC 2.1: KINETIC PARTICLE MODEL OF MATTER CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 1.4 Density 1.7 Kinetic energy 1.8 Pressure LEADS TO 2.2 Thermal properties 2.3 Energy transfer Behaviour of gases PARTICLE MODEL 1 · STATES OF MATTER The same particles are arranged and move differently in solids, liquids, and gases. Solid Liquid Gas Solid: fixed shape and volume; particles vibrate in place. Liquid: fixed volume, takes the shape of the container. Gas: fills the container and is easily compressed. 2 · GAS PRESSURE Gas pressure comes from particles colliding with the walls of the container. Each collision gives the wall a tiny push. Billions of collisions give a steady pressure. Heating speeds the particles up, so they hit harder and more often and the pressure rises. 3 · MOTION & BROWNIAN MOTION All particles are in constant, random motion. Brownian motion: large smoke specks are seen to jitter as fast, unseen air molecules strike them. This is evidence that molecules move quickly and randomly in all directions. Heating raises the average kinetic energy of the particles, which we measure as temperature. 4 · GAS LAWS & KELVIN EXTENDED At constant temperature, squeezing a gas into a smaller volume raises its pressure. p V = constant (Boyle’s Law) p V const. T Gas temperatures use the Kelvin scale: T (K) = θ (°C) + 273 0 K is absolute zero: particle motion is least.
TOPIC 2.1: KINETIC PARTICLE MODEL OF MATTER CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 1.4 Density 1.7 Kinetic energy 1.8 Pressure LEADS TO 2.2 Thermal properties 2.3 Energy transfer Behaviour of gases PARTICLE MODEL 1 · STATES OF MATTER The same particles are arranged and move differently in solids, liquids, and gases. Solid Liquid Gas Solid: fixed shape and volume; particles vibrate in place. Liquid: fixed volume, takes the shape of the container. Gas: fills the container and is easily compressed. 2 · GAS PRESSURE Gas pressure comes from particles colliding with the walls of the container. Each collision gives the wall a tiny push. Billions of collisions give a steady pressure. Heating speeds the particles up, so they hit harder and more often and the pressure rises. 3 · MOTION & BROWNIAN MOTION All particles are in constant, random motion. Brownian motion: large smoke specks are seen to jitter as fast, unseen air molecules strike them. This is evidence that molecules move quickly and randomly in all directions. Heating raises the average kinetic energy of the particles, which we measure as temperature. 4 · GAS LAWS & KELVIN EXTENDED At constant temperature, squeezing a gas into a smaller volume raises its pressure. p V = constant (Boyle’s Law) p V const. T Gas temperatures use the Kelvin scale: T (K) = θ (°C) + 273 0 K is absolute zero: particle motion is least.
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