Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Slow Motion Speech
Sneezing, coughing, and speaking all produce a spray of droplets capable of spreading COVID-19 and other respiratory illnesses. This Slow Mo Guys video is the latest demonstration in a long line of evidence for why wearing masks in public is such an important part of ending our current public health crisis. Also, I think we…
Floating in Levitating Liquids
When it comes to stability, nature can be amazingly counter-intuitive, as in this case of flotation on the underside of a levitating liquid. First things first: how is this liquid layer levitating? To answer that, consider a simpler system: a pendulum. There are two equilibrium positions for a pendulum: hanging straight down or pointing straight…
Hudson Bay Watercolors
Rivers sweep fresh water and sediment into the Hudson Bay in this satellite image. Dark brown plumes mark the mouths of several coastal rivers as they add to the cyclonic sediment flow around the bay and out the Hudson Strait. Paler swirls, like strokes of watercolors, mark turbulent mixing between the sediment-filled shallows and the…
“The Unseen Sea”
San Francisco’s picturesque fogs form “The Unseen Sea” in Simon Christen’s timelapse. Viewed at the right speed, the motion of clouds becomes remarkably ocean-like, with standing waves and surges against the hillside like waves crashing on a beach. Clouds in air don’t have the same surface tension effects as water waves in air, but, for…
Synchronizing Microfluidic Drops
In nature, synchronization occurs when oscillators interact. A group of metronomes shifting to tick in unison is a classic example. Here, the system is a microfluidic T-junction and the oscillators are the liquid interfaces along the narrower inlet channels. Systems like this one have long been used to create alternating droplets (Image 1), corresponding to…
Dead Water
In the days before motorized propulsion, sailors would sometimes find themselves slowed nearly to a stop by what they called ‘dead water‘. As discovered in laboratory experiments over a century ago by Vagn Walfrid Ekman, the dead water phenomenon occurs where a layer of fresh water exists over saltier water. The ship’s motion generates internal…
Hydrodynamic Bearings
If you twirl a glass syringe, it spins quite nicely, lubricated on a micron-thin layer of air. This is an example of a hydrodynamic bearing, a device where the viscosity of a fluid and relative motion of two closely-spaced surfaces provides the cushion necessary to keep the surfaces separate. In this video, Steve Mould explains…
Collecting Animal Tears
Like humans, most vertebrates rely on tear films to keep their eyes moist and protected from the environment. But compared to humans, some animals’ tears have superior staying power. The caiman, for example, can go up to 2 hours between blinks without their eyes drying out; in contrast, humans have to blink about 15 times…
Coalescing Drops
This year’s Nikon Small World in Motion competition was won by fluid dynamics! The first place video shows droplets on a superhydrophobic surface coalescing. The droplets are a mixture of water and ethanol. Their initial merger creates a ripple of waves that’s followed by a ghostly vortex ring that jets into the interior. Previous research…
Colorful Kelvin-Helmholtz Clouds
Like breaking waves at the beach, these wavy clouds curl but only for a moment. The photo was captured near sunset on a late August evening in Arlington, MA. This short-lived cloud shape forms due to the Kelvin-Helmholtz instability, which is driven by shear forces between two layers of air moving at different speeds. The…