Diffraction from a Regular Array of Apertures
When light passes through a single aperture, the resulting diffraction pattern is a broad central bright spot — the Airy disk — surrounded by faint concentric rings. Place hundreds or thousands of identical apertures in a regular array, however, and something remarkable happens: intensity concentrates into sharp, intense peaks at specific directions, while the rest […]
The Foucault Pendulum and Earth’s Rotation
In 1851, Léon Foucault hung a 67-meter wire from the dome of the Panthéon in Paris, attached a heavy iron ball to its end, and gently set it swinging. Over the next several hours, observers watched the plane of oscillation slowly rotate — not because any force was twisting the pendulum, but because the Earth […]
Halbach Arrays and Magnetic Levitation
A Halbach array is a cleverly engineered arrangement of permanent magnets in which the magnetization direction rotates progressively from one magnet to the next. The result is striking: the magnetic field concentrates strongly on one side of the array while nearly canceling itself on the other. This asymmetry, first identified by John Mallinson in 1973 […]
Chladni Figures: Visual Music in Vibration
When a metal or glass plate is set into vibration and lightly dusted with fine sand, the grains migrate along specific paths and settle into striking, symmetric patterns. These shapes — known as Chladni figures, after the German physicist Ernst Florens Friedrich Chladni (1756–1827) — are a direct visual map of the plate’s vibrational mode […]
Vortex Rings: Persistent Toroidal Structures
When you blow a smoke ring or watch a dolphin craft an underwater bubble loop, you are witnessing one of fluid dynamics’ most elegant structures: the vortex ring. This toroidal vortex can travel through a medium under its own power, remain coherent for seconds, and even interact with other rings in striking ways. Understanding the […]
Froude Number — Waves, Hydraulic Jumps & Dynamic Similarity
The Froude number: definition, physical meaning, hydraulic jumps, ship hull speed, and dynamic similarity with fully worked examples.
Weber Number — Surface Tension vs Inertia
The Weber number: surface tension vs inertia in droplet formation, jet stability, atomization, and IYPT 2027 P7 connection.
Strouhal Number — Vortex Shedding & Fluid-Structure Interaction
The Strouhal number: Kármán vortex street, aeolian tones, power line vibrations, fish locomotion, and IYPT 2027 connections.
Reynolds Number — From Laminar Flow to Turbulence
What is the Reynolds number? Definition, physical meaning, worked examples (blood, air, bacteria), connection to IYPT problems, and derivation from Navier-Stokes. With dynamic similarity and drag crisis explained.
Hagen-Poiseuille Flow — Why r⁴?
Why does blood pressure rise so dangerously when arteries narrow? The answer lies in the Hagen-Poiseuille law: flow scales as the fourth power of radius. Step-by-step derivation with clear physics.