63 questions · 33 almanac · 2 findings

Fluid Dynamics

The physics of liquids and gases in motion.

Almanac The Capillaries Decide for Themselves
  • What did Krogh notice was different between the capillaries of a resting frog and a working one?
  • How do capillaries actively regulate blood flow to match a tissue's metabolic demand?
  • Why did earlier investigators find the precision of capillary regulation implausibly convenient?
Almanac Where the Interesting Chemistry Happens
  • What did Langmuir discover about how molecules arrange themselves in single layers on a surface?
  • Why does surface chemistry behave so differently from the chemistry of a material's interior?
  • How does Langmuir's surface science help explain how cell membranes stay selectively permeable?
Almanac A Chain No One Believed Was Real
  • What evidence from viscosity measurements eventually convinced chemists that Staudinger's long-chain model was correct?
Almanac The Stars and the Hard Drive, Explained
  • What is magnetohydrodynamics, and why did Hannes Alfvén's theory of it apply to solar flares and fusion reactor plasma alike?
  • Why did Lev Landau and other physicists initially dismiss Alfvén's plasma theories?
Almanac Order Feeding on Disorder
  • Why doesn't the spontaneous formation of Bénard convection cells violate the second law of thermodynamics?
Almanac Why Toast Lands Buttered-Side Down
  • What two physical factors did Matthews identify as the reason toast tends to land buttered-side down?
  • Why does standard table height give toast just enough time to complete half a rotation before hitting the floor?
  • According to Matthews, what would you have to change about your table or your toast to beat the odds?
Almanac The Physics of Not Losing Your Biscuit
  • How did Len Fisher model biscuit dunking as a problem in capillary action and porous media?
  • What determines whether a teapot spout drips instead of pouring cleanly?
  • What balance of forces decides when a dunked biscuit collapses rather than holding together?
Almanac A Vortex Inside the Shower
  • Why does a shower curtain billow inward and cling to a bather when hot water runs?
  • How does Bernoulli's principle explain the low-pressure vortex created by a shower spray?
  • What method did David Schmidt use to model and confirm the shower curtain vortex?
Almanac Beer Foam Obeys a Decay Law
  • What is exponential decay, and what other natural phenomena does it also describe?
  • How did Arnd Leike measure the half-life of beer foam, and why did it vary by beer style?
Almanac Syrup Swims No Slower Than Water
  • How did Cussler and Gettelfinger raise the viscosity of a swimming pool for their experiment?
  • Why did swimmers move at the same speed in the thickened water as in normal water?
  • What longstanding debate in fluid dynamics did this experiment settle?
Almanac The Choreography Hiding on a Metal Surface
  • What ultrahigh-vacuum techniques did Gerhard Ertl use to watch molecules on a metal surface?
  • How did Ertl's research turn catalysis from an industrial craft into a rigorous science?
Almanac Your Stride Is Resonating With Your Coffee
  • Why does coffee tend to spill from a mug at the worst possible moment while walking?
  • How does the natural sloshing frequency of coffee coincide with the rhythm of human walking?
  • What practical strategies did Krechetnikov and Mayer find reduce coffee spillage while walking?
Almanac The Banana Peel, Finally Measured
  • What substance does a banana peel release under pressure that makes it so slippery?
  • How did the researchers compare the slipperiness of banana peel against orange and apple peel?
  • How does the friction coefficient of a banana peel compare to wet ice or a waxed floor?
Almanac Every Mammal Empties in Twenty-One Seconds
  • Why does bladder-emptying time stay roughly constant across mammals of wildly different sizes?
  • How does urethra scaling keep flow rate proportional to bladder volume?
Almanac Walk Backward, Spill Less Coffee
  • Why does walking forward cause coffee to slosh out of a cup more than walking backward?
  • What is the resonance mechanism that couples a person's gait to the sloshing frequency of a liquid?
  • How did Jiwon Han confirm the backward-walking effect experimentally?
Almanac Is a Cat a Liquid?
  • What is the Deborah number, and how does it distinguish a liquid from a solid?
  • What makes Fardin's cat-fluidity paper a genuine application of rheology rather than just a joke?
Almanac Anchovies Stir the Ocean Too
  • What role does ocean mixing play in climate and nutrient distribution?
  • How did Bieito Fernández Castro's team measure the contribution of spawning anchovies to ocean turbulence?
  • Why had fish-generated turbulence been left out of ocean circulation models before this study?
Almanac First to the Moon's Shadowed Pole
  • Why is the Moon's south pole considered scientifically significant, and what might its permanently shadowed craters contain?
Almanac Hair Whorls Ignore the Equator
  • Why does the Coriolis force influence large systems like ocean currents and cyclones but not something as small as a hair follicle?
Almanac A Dead Trout Swims Upstream
  • How can a dead trout placed in flowing water move upstream without any muscular effort of its own?
  • What role does the body's passive flexibility play in converting stream vortices into forward thrust?
Finding Hydromechanical field theory of plant morphogenesis
  • How does treating plant tissue as a poromorphoelastic medium explain the coupling between water absorption and cell wall expansion during growth?
  • Why do growing regions of a plant tissue behave as hydraulic sinks, and what non-local effects does this create across the tissue?
  • How can competing growth regions in a plant tissue draw water away from each other through shared water potential gradients?