Tag Archives: Liquid

The thick and thin of viscosity

Viscosity is a liquid’s property of resisting deformation, such as flow. At home, you probably know this property as the ‘thickness’ of a fluid. The word comes from the Latin word “viscum”, meaning ‘mistletoe’, the berries of which were used in ancient times to create glue.

Water doesn’t behave like that — that’s viscosity.
Image via Pixabay.

Viscosity can be a weird concept to wrap your head around, because it makes fluids act not like fluids. Such a large part of our intuitive understanding of fluids relies on them behaving a certain way. Water, the quintessential liquid, flows immediately when poured; it takes the shape of its container, and if there’s no container, it spills everywhere. It gets absorbed by sponges or soil; it bubbles with gusto when boiling.

On the other hand, pitch can easily be confused for a solid. Because it’s so highly viscous, it barely flows, has quite an easy time maintaining its rough shape, and barely percolates through either soil or sponges.

So let’s see what this property which makes fluids un-fluid-like is.

The source of viscosity

In strictly physical terms, viscosity is a fluid’s shear stress over its shear rate, and is expressed in poise (P), a measure of pressure per second. It shows how much force per unit of area you need to apply to make a fluid move (shear stress) and how the internal layers of that fluid will move in respect to one another (shear rate).

In short, it shows how much energy you need to apply to make a fluid flow. The field of science that studies the flow patterns of matter is called rheology from the Greek term “rheo”, meaning ‘flow’.

Viscosity is the product of internal friction between the fluid’s molecules. Both gases and liquids have viscosity, but the molecules in liquids are packed in more tightly — making them interact more and, thus, have higher viscosity than gases.

Viscosity makes fluids flow more slowly, but also stick strongly to solids.
Image via Pixabay.

Shear rate is important in this equation because it describes how successive ‘layers’ of molecules in fluid interact with one another. A great way to see it in action is to try pouring honey out of a jar. It flows much more slowly than water because it is more viscous than it. But you’ll also notice that the honey in the center will flow out before the honey on the sides of the jar does as well.

This is due to the friction between the layers we mentioned earlier. Honey molecules that are right next to the glass will be attracted to the molecules in glass strongly enough that they’re basically stationary (solids are dense bunches of immobile molecules). They will generate friction with other honey molecules, in turn.

Friction always opposes the direction of motion so, in effect, this stops the fluid from sliding off the glass. Further layers of honey also experience friction, but against layers of fluid that are more mobile than the glass — so there’s less friction. Keep the model going and honey right in the middle of the jar will be most flowy because it’s experiencing little friction (against other relatively mobile molecules of honey).

It doesn’t only slow down pouring fluid — viscosity also prevents objects from passing through. A spoon will go through water with almost no effort, but not so through honey.

File:Air bubbles. Honey.jpg
Air bubbles rise quickly through soda, but have a hard time ascending though honey.
Image via Wikimedia user Sichnoy.

A good way to think about viscosity is that all the molecules in a fluid have hands, and they’re using them to hold onto their neighbors. The better these molecules can latch on, the more viscous the substance will be. In physical terms, these hands make up the cohesive force, being generated by chemical and physical interactions between molecules.

Types of viscosity

True solids cannot be vicious. In solids, molecules cannot really move in relation to one another. If one moves, they all move, or break apart. Since viscosity is defined in relation to flow (where particles move independently from one another), it can’t by definition be applied to a true solid. It would be like trying to define what light tastes like. That being said, not all fluids are born equal in regard to viscosity.

The most common class of viscous material you’ll encounter are Newtonian fluids. These always behave like fluids should, having a relatively constant viscosity. Although their resistance to flow does increase as more force is applied, this is proportional to the force being applied. Newtonian fluids, for all intents and purposes, keep acting like fluids no matter how much force you exert on them.

Air is a Newtonian fluid, although viscosity has no bearing on the speed of sound through air.

Hitting a balloon filled with colored water (bottom) makes it splatter everywhere. A mixture of starch and water, however (top, a non-Newtonian fluid,) becomes almost solid-like and breaks apart. Also, note how much each slows the bat on impact.
Image credits Reddit user u/Lord_Rae.

On the other end of the spectrum, we have non-Newtonian fluids. With them, viscosity varies very strongly with the force being applied, but not necessarily in the same way between different materials. Silly putty is a good example; left to itself, it’s somewhat flabby, but when you apply force against the putty, it hardens up. There are three large categories of non-Newtonian fluids: dilatant (apparent viscosity increases with exerted force), pseudoplastic (apparent viscosity decreases with exerted force), and generalized Newtonian fluids (which, ironically enough, are non-Newtonian). Ketchup is also non-Newtonian, but it becomes less viscous when force is applied.

Electrorheological and magnetorheological fluids increase their viscosity in the presence of electrical and magnetic fields respectively and can become near-solid under the right conditions, and quickly reverting back to a liquid if needed.

What has viscosity ever done for you?

A mixture of corn starch and water (similar to the previous one) exhibiting non-Newtonian properties.
Credits Youtube / ScienceMandotcom.

Perhaps one of the most important impacts viscosity has on our lives is in our biology. The size, shape, and structure of our hearts, circulatory system and virtually every other tissue, as well as the structures and functionality of our cells, are all shaped to take advantage of or work around viscosity. Our immune system relies in no small part on our lymph channels. Lacking the propelling power of our heart, lymph vessels have to be designed around the viscosity of lymph to keep everything in working order.

Each morning, when you go brush your teeth, it’s viscosity preventing the paste in the tube from splattering everywhere. Without viscosity, your ketchup would drain out of the bottle almost instantly, and the lubricants in your car wouldn’t be able to coat (and thus, lubricate) anything.

Viscosity is what makes liquids want to pool together, and it was a key player in applications such as pill manufacturing. Industries involved in the production of food, chemicals, adhesives, biofuels, paints, medicine, and petroleum processing all keep a close eye on the viscosity of their products.

Finally, viscosity is always affecting us, although we’ve evolved to not feel it. But whenever you make even the slightest of motions, the air’s viscosity works against it — it produces ‘air drag’. Swimming, too, lets you experience a somewhat more concentrated flavor of viscosity.

Personally, I find that processes happening mostly in the background of our awareness, the unsung underdogs of physics (such as viscosity) are the most fascinating ones to study. We may take them for granted, we may not even be aware they exist, but they silently play a part in everything we do. Even a ‘humbler’ one, like viscosity, has directly shaped life on Earth into what it is today.

It Is Possible Jupiter Could Support Life, Scientists Say

Jupiter and its shrunken Great Red Spot. Credit: Wikimedia Commons.

Jupiter and its shrunken Great Red Spot. Credit: Wikimedia Commons.

A new factor has been added to the debate on whether or not living organisms could exist on Jupiter. You probably know Jupiter is a Jovian planet, a giant formed primarily out of gases. So how could alien life be able to exist in an environment where most of the phases of matter are absent? The answer is simply found in the element of water.

Within the rotating, turbulent Great Red Spot, perhaps Jupiter’s most distinguishable characteristic, are water clouds. Many of the other clouds in this enormous perpetual storm are comprised of ammonia and/or sulfur. Life theoretically cannot be sustained in water vapor alone; it thrives in liquid water. But according to some researchers, the fact alone that water exists in any form on the planet is a good first step.

The Great Red Spot is still a planetary feature which stumps much of the scientific community today. As it has been observed for the past century and a half, the Great Red Spot has been noticeably shrinking. The discovery of water clouds may lead to a deeper understanding of the planet’s past, including whether or not it might have sustained life, as well as weather-related information.

Some scientists have pondered the possibility that, due to the hydrogen and helium content in its atmosphere, Jupiter could be a diamond-producing “factory.” They have further speculated that these diamonds could enter into a liquid state and a rainfall of liquid diamonds would be in the Jovian’s weather forecast.

Likewise, the presence of water clouds means that water rain (a liquid) is not entirely impossible. Máté Ádámkovics, an astrophysicist at Clemson University in South Carolina, had this to say on the matter:

“…where there’s the potential for liquid water, the possibility of life cannot be completely ruled out. So, though it appears very unlikely, life on Jupiter is not beyond the range of our imaginations.”

Scientists are acting accordingly, researching the part which water plays in the atmosphere and other natural systems on Jupiter. They remain skeptical but eager to follow up on the new discovery. They shall also strive to find out just how much water the planet really holds.

Three Old Scientific Concepts Getting a Modern Look

If you have a good look at some of the underlying concepts of modern science, you might notice that some of our current notions are rooted in old scientific thinking, some of which originated in ancient times. Some of today’s scientists have even reconsidered or revamped old scientific concepts. We’ve explored some of them below.

4 Elements of the Ancient Greeks vs 4 Phases of Matter

The ancient Greek philosopher and scholar Empedocles (495-430 BC) came up with the cosmogenic belief that all matter was made up of four principal elements: earth, water, air, and fire. He further speculated that these various elements or substances were able to be separated or reconstituted. According to Empedocles, these actions were a result of two forces. These forces were love, which worked to combine, and hate, which brought about a breaking down of the elements.

What scientists refer to as elements today have few similarities with the elements examined by the Greeks thousands of years ago. However, Empedocles’ proposed quadruplet of substances bares resemblance to what we call the four phases of matter: solid, liquid, gas, and plasma. The phases are the different forms or properties material substances can take.

Water in two states: liquid (including the clouds), and solid (ice). Image via Wikipedia.

Compare Empedocles’ substances to the modern phases of matter. “Earth” would be solid. The dirt on the ground is in a solid phase of matter. Next comes water which is a liquid; water is the most common liquid on Earth. Air, something which surrounds us constantly in our atmosphere, is a gaseous form of matter.

And lastly, we come to fire. Fire has fascinated human beings for time beyond history. Fire is similar to plasma in that both generate electromagnetic radiation such as light. Most flames you see in your everyday life are not hot enough to be considered plasma. They are typically considered gaseous. A prime example of an area where plasma is formed is the sun. The ancient four elements have an intriguing correspondent in modern science.

Ancient Concept of Dome Sky vs. Simulation Hypothesis

Millennia ago, people held the notion that his world was flat. Picture a horizontal cooking sheet with a transparent glass bowl set on top of it. Primitive people thought of the Earth in much the same way. They considered the land itself as flat and the sky as a dome. However, early Greek philosophers such as Pythagoras (c. 570-495 BC) — who is also known for formulating the Pythagorean theorem — understood that Earth was actually spherical.

Fast forward to the 21st century. Now scientists are considering the scientific concept of the dome once again but in a much more complex manner.

Regardless of what conspiracy lovers would have you believe, the human race has ventured into outer space, leaving the face of the Earth to travel to the stars. In the face of all our achievements, some scientists actually question if reality is real, a mindboggling and apparently laughable idea.

But some scientists have wondered if we could be existing in a computer simulation. The gap between science and science fiction starts to become very fine when considering this.

This idea calls to mind classic sci-fi plots such as those frequently played out in The Twilight Zone in which everything the characters take as real turns out to be something entirely unexpected. You might also remember the sequence in Men in Black in which the audience sees that the entire universe is inside an alien marble. Bill Nye even uses the dome as an example in discussing hypothetical virtual reality. This gives one the feeling that he is living in a snowglobe.

Medieval Alchemy vs. Modern Chemistry

The alchemists of the Middle Ages attempted to prove that matter could be transformed from one object into an entirely new object. One of their fondest goals they wished to achieve was the creation of gold from a less valuable substance. They were dreaming big, but such dreams have not yet come to fruition. Could it actually be possible to alter one type of matter into another?

Well, modern chemists may be well on their way to achieving this feat some day. They are pursuing the idea of converting light into matter, as is expressed in Albert Einstein’s famous equation. Since 2014, scientists have been claiming that such an operation would be quite feasible, especially with extant technology.

Einstein’s famous equation.

Light is made up of photons, and a contraption capable of performing the conversion has been dubbed “photon-photon collider.” Though we might not be able to transform matter into other matter in the near future, it looks like the light-to-matter transformation has a bright outlook.

Squished-booms: looking at the behavior of underwater explosions

Some things go boom, others don’t. The first category is definitely more fun.

Other things go boom in unusual places — these are arguably the best.
Image via Youtube / Slow Mo Guys.

A material explodes when it increases in volume rapidly and releases a lot of energy. The most usual energy storage used to create explosives is of the chemical kind, but explosives can be created using atomic, electrical, or mechanical sources. The characteristic boom or bang of an explosion is how your ears pick up on the “changing volume” part of the explosion, the shockwave. This is the force that lends explosions their destructive nature. The biggest part of an explosive’s energy is expended as light, heat, and work.

Not all explosions are made the same. The medium in which detonation takes place has a huge influence on the way the explosion and its shockwaves behave. And, while surface explosions are pretty ubiquitous in movies, underwater explosions aren’t — which is a shame, because they’re really pretty.

So let’s watch some

First thing first: explosions are inherently hard to enjoy properly — they’re ephemeral, gone in a flash of the eye.

That is, unless you film it thousands of times faster than the eye can see, which is exactly what the Slow Mo Guys did. They took a firecracker, set it alight, then submerged it in a fish tank to blow up — all under the watchful lens of a 120.000 fps high-speed camera. The resulting reel slows the detonations down enough for us to observe some basic principles of underwater explosions. I’ve taken the explosions and turned them into gifs below, but the whole video is pretty good and you should watch it.

Here are the firecrackers exploding.

Image via Youtube / Slow Mo Guys.

Underwater detonations spread out in the begging, creating a hollow sphere inside the liquid. This soon collapses in on itself, as water rushes to fill the gap.

Image via Youtube / Slow Mo Guys.

This happens for two reasons. One, water is much denser than air, so it’s a lot harder to push around. Then there’s the fact that water, unlike air, can’t be compressed. This is the same property that underpins hydraulic systems (incompressibility) and because of it, the firecracker has to act on the fluid as a whole. In essence, this means that it has to perform work on a much denser, much larger medium. This property is also used by SWAT teams and military personnel to breach doors in the form of water impulse charges — water here is used to direct the force of the blast evenly onto a surface.

A firecracker set off in normal conditions can propel gas and fragments a few meters away, but underwater the explosion has enough energy to expand only a few centimeters across.

In this gif, the detonation took place closer to the water’s surface and you can actually see the liquid pouring in on the collapsing bubble.

Image credits Youtube / Slow Mo Lab.

Apart from this shot, the video itself doesn’t add that much from the one above (the guy shooting it does have a necktie though). You can see it here.

The shockwaves

The gases released during detonation are then squashed by the liquid’s weight. This compression-explosion interplay can become quite lively, as the water compresses the gas as far as it can, then gets pushed back, and repeat. The collapse of the hollow bubble generates the first shock wave. Secondary shock waves are created as gas and water wrestle.

TheBackyardScientist can help explain with his liquid nitrogen bomb. He only shot with a 240 fps camera, so you can’t actually see the liquid being pushed during the explosion — but you can see the awesome gas-water play after it.

Here are some highlights.

Wub dub dub dub.
Image via Youtube / TheBackyardScientist.

Wub dub dub dub, the sequel.
Image via Youtube / TheBackyardScientist.

TBS conveniently placed some balloons around the point of detonation, to pick up on the shockwaves’ motions. As you can see, there’s a lot of motion going on throughout the fluid as the gas gets compressed then expands.

The surface

So this one will feature a nuke ’cause its the last part — why not go big?


As you can see, the highest point the water is thrown upwards lies directly above the point of detonation — the center point of the shockwave. If you pause the video or look at the thumbnail image you’ll see that the shape of the column of water being pushed upwards follows an exponential curve — not the round shape we saw in the bubbles.


Edible coating can empty every last drop of sticky liquids like ketchup, honey or syrup

coating hydrophobic

Credit: ACS

No matter how much you try, there will always be some drops of ketchup stuck to the bottom and walls of the bottle. Same with just about any sticky, gooey liquids like honey or syrup. Not content to live any longer with such nuisance, a team of researchers developed a safe coating derived from natural materials that can effortlessly slide liquids off. Virtually any liquid can be empty from a container layered in this coating.

An elegant solution to a sticky problem

What the Colorado State University researchers essentially did was to develop a superhydrophobic coating — a nanoscopic surface layer that repels water. Examples of such coatings abound in nature where some plants, such as the Lotus leaf, and some insect wings employ it. Artificial superhydrophobic coatings have been made using materials like precipitated calcium carbonate, silica nanocoating or manganese oxide polystyrene.

[panel style=”panel-success” title=”Why some things are sticky” footer=””]Stickiness depends on the interface of two materials. Honey in itself, for instance, isn’t sticky. It might be when it touches your hand, but not on teflon.

There are several reasons why objects can be sticky, or display adhesive properties. One reason is that certain forces, called Van Der Walls forces, occur between the object and your finger. The molecules are attracted to each other, so it takes force to separate the two once they have come in contact.

Another reason can be more mechanical in nature. For example, if an object’s surface is soft and deformable, when pressed against a rough object, it will deform and ooze into cracks and crevices. Now, to separate the two objects requires that either (1) the soft material get pulled out of cracks and crevices, or (2) the soft material has to get torn apart.

A third mechanism can be the formation of new chemical bonds between the adhesive and the substrate. Such adhesives tend to be very powerful, and the adhesion is harder to reverse. Many adhesives rely on more than one mechanism for their properties.

What’s different in this case is that the coating is 100 percent safe because it was made from carnauba wax and beeswax, two natural FDA-approve edible materials. Previously, the FDA banned three perfluorinated compounds (PFCs) which were used in pizza packaging to keep the food from greasing because they were deemed unsafe.

The researchers tested the superhydrophobic surface with coke, pancake syrup, Lipton tea, Gatorade, ketchup, and water. Each liquid beaded into a sphere which could be rolled off by gravity alone, leaving no trace behind. The same coating was then tested in a real life situation by layering it inside polystyrene cups. The cups were filled with chocolate syrup or honey and again left no trace after the contents were emptied.

The coating breaks when exposed to a harsh or abrassive environment, though, so there’s some room for improvement. Who am I kidding, it looks almost perfect already. Where do I sign up?

Reference: Wei Wang et al. “Superhydrophobic Coatings with Edible Materials.” ACS Appl. Mater. Interfaces 8 (29): 18664–18668. Published: 12-July-2016. DOI: 10.1021/acsami.6b06958

First porous liquid could revolutionize carbon capture

Research at the Queen’s University Belfast has produced a major (and mind-bending) breakthrough, in the form of the first synthesized porous liquid. The new material has the potential for a massive range of new technologies including carbon capture.

Researchers at Queen’s University Belfast, Northern Ireland, UK, have made the world’s first porous liquid by designing a molecule shape that can’t occupy space efficiently, thus creating ‘holes’ in the liquid.
Image via phys

Researchers in the School of Chemistry and Chemical Engineering at Queen’s, along with colleagues at the University of Liverpool and other international partners have created the new liquid and found that it can dissolve an unusually large quantity of gas.The secret? Gas molecules are shaped into little cages that trap gases in ‘holes’ in the liquid.

“Materials which contain permanent holes, or pores, are technologically important. They are used for manufacturing a range of products from plastic bottles to petrol. However, until recently, these porous materials have been solids,” says Professor Stuart James of Queen’s School of Chemistry and Chemical Engineering.

“Liquid solvents, rather than porous solids, are the most mature technology for post-combustion capture of carbon dioxide because liquid circulation systems are more easily retrofitted to existing plants.”

The material is the result of a three-year research project and could pave the way towards many more efficient and greener chemical processes, the team citing carbon capture as one of their intended uses for the porous liquid.

“What we have done is to design a special liquid from the ‘bottom-up’ – we designed the shapes of the molecules which make up the liquid so that the liquid could not fill up all the space. Because of the empty holes we then had in the liquid, we found that it was able to dissolve unusually large amounts of gas. These first experiments are what is needed to understand this new type of material, and the results point to interesting long-term applications which rely on dissolution of gases,” he added

“A few more years’ research will be needed, but if we can find applications for these porous liquids they could result in new or improved chemical processes. At the very least, we have managed to demonstrate a very new principle – that by creating holes in liquids we can dramatically increase the amount of gas they can dissolve. These remarkable properties suggest interesting applications in the long term.”