Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
What is Pressure?
Pressure is a critical concept in fluid dynamics – a driving force behind everything from weather patterns to lift on a wing. But where does pressure come from? Like many macroscopic forces dealt with in fluid dynamics, pressure can be traced to the effects of individual molecules within a fluid. Kinetic theory describes gases as…
Beads on a String
Adding just a small amount of polymers to a liquid can drastically change its behavior. The polymers make the liquid viscoelastic, meaning that, under deformation, the liquid shows behaviors that are both viscous (like all fluids) and elastic (i.e. able to resume its original shape, like a rubber band). These properties are particularly identifiable under…
H Booms
Holidays involving fireworks deserve high-speed videos of hydrogen explosions. Although Periodic Table of Videos focuses on the chemistry involved in setting hydrogen on fire, there are some lovely fluid dynamics on display, too. There’s turbulence, combustion (obviously), and, if you watch closely, you can even see the initial vorticity caused by the rubber’s burst twisting…
Happy 4th of July!
physicsindrops: Happy 4th of July.
Self-Siphoning Stream of Beads
Pull a bit of a long chain out of a container, and you’ll quickly find the beads take on a life of their own, siphoning out of the jar while leaping and looping in the air. Some of the dynamics are clear – the ever-growing free end of the chain has weight enough to pull…
Dancing Jets
Vibrating a gas-liquid interface produces some exciting instability behaviors. The photo above shows air and silicone oil vibrated vertically within a prism. For the right frequencies and amplitudes, the vibrations produce liquid jets that shoot up and eject droplets as well as gas cavities and bubble transport below the interface. To see a similar experiment…
Hydrophobia
Hydrophobic literally means water-fearing, and, once a surface is treated with a hydrophobic coating, the effect on water droplets is stark. The tendency of the non-polar hydrophobic molecules to repel the polar water molecules leads to high contact angles – which make the droplets almost spherical as they glide along the surface. The droplets dance…
How Flames Expand
Combustion is a remarkably complicated phenomenon fluid dynamically. The schlieren images above illustrate a couple of the variables that affect flame propagation. The top image shows an idealized, essentially spherical flame expanding in a quiescent hydrogen-air mixture at atmospheric pressure. The middle flame is expanding in a high-pressure environment, similar to an internal combustion engine.…
Studying Coughs
Bioaerosols–tiny airborne fluid droplets generated by coughing or sneezing–are a major concern for the spread of contagions like influenza. It may be possible, however, to mitigate some of these effects by manipulating biological fluid properties. The video above shows an experimental model of a cough, complete with the generation of bioaerosols from some fake human…
Hanging Liquids
A horizontal filament of viscous liquid hanging between two plates stretches under gravity. The photo above is a composite showing the stretching of a single thread over several time steps. The fluid forms a catenary, the same shape as a hanging chain or cable when supported only at its ends. This behavior is confined to…