This Is Why … Microscopic but Mighty Cyanobacteria Deserve Our Respect

Science Twitter is a great place – for education and entertainment. This ‘cyanobacteria meme’ was tweeted by Jaida Elcock, also known as @soFISHtication, on June 15, 2020, and quickly racked up more than 1000 retweets and 5000 likes. As a physicist with a somewhat sketchy memory of first-year biology, I felt like I needed a bit of a refresher on the whole photosynthesis thing. Next thing I know, I’d fallen down a fascinating rabbit hole, learning a ton about some very cool research into generating electricity from biophotovoltaic cells. But, first, we need to back up a bit.

I freely admit that I fall into the naïve category of “everyone” here in thinking that trees and greenery are the suppliers of our oxygen. Or, I should say, I thought that, until this tweet led me to discover that photosynthesizing trees and land-based plants actually only provide about half of our oxygen. The other half comes from phytoplankton, an eclectic mix of (mostly) single-celled creatures that live in fresh and salt water (see illustration at the top). Cyanobacteria are just one form; collectively these organisms can be thanked for not only producing the air we breathe, but also for forming the foundation of the aquatic food chain.

Cyanobacteria in water, Shutterstock.com image 757041874

Now that we are all in on @soFISHtication’s joke, you may be wondering how physics enters this story. Don’t get me wrong, I’m always happy to learn something new no matter what the subject, but my physicist tendencies draw me toward physical systems and applications. So, the papers that grabbed my eye when digging into this topic were all about the possibility of harnessing the photosynthesizing power of these teeny little organisms to generate electricity, in a nascent field called biophotovoltaics. When cyanobacteria use sunlight to form sugar and oxygen, there are steps along the way that generate electrons. The idea is to intercept some of these electrons and send them into a connected electrical circuit, thereby generating a current out of sunlight, carbon dioxide, and water. It really doesn’t get much greener than that in terms of electrical generation – microorganisms doing what microorganisms do, but providing us with a little bit of electricity as a by-product!

And when I say a little bit, I do mean a little bit. The devices that have been built so far have peak currents that are measured in microamps, which means that biophotovoltaics are not going to single-celledly solve the world’s energy problems. But, as with any young field, there are rapid developments occurring to improve both the overall efficiency as well as the total output of these systems. One paper published last month in Nano Letters by a team from South Korea coupled cyanobacteria to a nanoscopic structure consisting of gold (Au) particles and zinc-oxide (ZnO) rods. Their setup was designed to expand the range of light frequencies that could be converted to electricity, as well as to amplify the signal from the organisms.

A schematic of the living solar cell reported last month in Nano Letters. The circled numbers refer to different pathways for extracting electrons from the photosynthesis chain and ITO is the specific glass slide used as the base. Reprinted with permission from Nano Lett. 2020, 20, 6, 4286–4291. Copyright © 2020 American Chemical Society.

Unlike conventional solar-powered devices, biophotovoltaics (BPVs) generate current both when the light is shining and when it isn’t, since electrons are generated during darkness from a chemical reaction involving the sugars formed by photosynthesis. And, although it almost sounds like science fiction, a British team reported in Nature Communications in 2017 that they had successfully produced a BPV using an inexpensive commercial inkjet printer to print a ‘bio-ink’ of cyanobacterial cells onto a carbon nanotube conducting surface. The device provided enough current to generate flashes in a connected LED light, suggesting that their paper-based printed BPV could work as an environmentally-friendly power supply for biosensors that only require intermittent bursts of energy. Printing BPVs is certainly a tantalizing hint that this technology could scale, with these authors suggesting the possibility of “bioenergy wallpaper” in our future.  

As I said at the beginning, this particular rabbit hole has been a fascinating exploration into a world I knew nothing about. These studies really did blow my mind: fabricating devices that extract electrons from individual living cells is truly a technological marvel. I’m looking forward to following this work in the future and learning much more about the microscopic but mighty cyanobacteria. Thanks Twitter!

References:

Electricity generation from digitally printed cyanobacteria (2017) Marin Sawa, Andrea Fantuzzi, Paolo Bombelli, Christopher J. Howe, Klaus Hellgardt & Peter J. Nixon Nature Communications volume 8, Article number: 1327 (2017)  https://www.nature.com/articles/s41467-017-01084-4

Biophotovoltaics: Green Power Generation From Sunlight and Water (2019) J. Tschörtner, B. Lai, and J. O. Krömer Frontiers in Microbiology 10:866 doi: 10.3389/fmicb.2019.00866

A Broadband Multiplex Living Solar Cell (2020) M. J. Kim, S. Lee, C.-K. Moon, J.-J. Kim, J. R. Young, Y. S. Song Nano Letters doi: 10.1021/acs.nanolett.0c00894

https://ucmp.berkeley.edu/bacteria/cyanointro.html

https://earthobservatory.nasa.gov/features/Phytoplankton

https://www.nationalgeographic.com/news/2004/6/source-of-half-earth-s-oxygen-gets-little-credit/

This Is Why … Zebras Have Stripes

(“IMG_2095” by expat696969 is licensed under CC0 1.0)

Ok, I’ll admit that I was more than a little skeptical when my 15-year-old daughter asked me to buy a zebra-print flysheet for her horse. I may even have scoffed, saying something along the lines of “Why would you want to make your horse look so silly?” When Hannah replied: “Because – SCIENCE!”, I knew that I had to do a little digging. Well played, Young Grasshopper, well played.

Imagine my surprise when I learned that, as recently as 2012, the purpose of zebra stripes was still a highly-contested issue. Such a simple question, asked by biologists for centuries (including Charles Darwin), with no definitive answer. Sure, there were plenty of theories (camouflage, confusion of predators, social interaction, heat control, sign of overall health, protection from insects), but nothing had been experimentally confirmed.  

And then along comes a team of scientists from Hungary and Sweden, conducting field experiments to test the theory that stripes protect zebras from biting, disease-carrying insects. Starting with pans of oil with different black and white patterns at the bottom, and then moving on to 3D animal models covered in mouse-trap glue, there was a significant difference in the number of horseflies collected for stripy surfaces versus solid. Of the four “horses” tested, the black one collected 61% of the flies, the brown horse accounted for 36%, followed by the white model at a little more than 2% of the total. The model that was painted like a zebra collected less than 1% of all the flies stuck to the gluey surfaces!

Our Hungarian-Swedish crew returned to the same Hungarian horse farm a few years later. This time, however, they brought mannequins that were either brown, beige, or brown with white stripes, to test whether body painting typically seen in tribes living in Africa, Australia, Papua New Guinea, and North America deterred horseflies. Their results, again, were compelling. The brown mannequin was 10 times more attractive to horseflies than the body-painted model, whereas the beige figure was twice as attractive as the one with stripes. It might be time to outfit the family in stripes for our next spring fishing trip into the backcountry of Algonquin Park!

From https://royalsocietypublishing.org/cms/asset/eb95900e-83f8-452b-9ed6-66cf4e4bd563/rsos181325f03.jpg

But why? Why would a horse or a person that is half black and half white (approximately) attract significantly fewer horseflies compared to the same models that were either all black or all white? The answer to this was addressed by another team led by Tim Caro from University of California, Davis. By painstakingly observing horses and zebras grazing in adjacent paddocks in Somerset, England, they concluded that the stripes confuse the poor little flies when they get close – they tend to come in too fast, land less often, and sometimes just bounce off haphazardly – compared to the more frequent successful landings on their non-stripy neighbours. (Get it? “Neigh-bours”)

The Caro team also covered the horses in three different sheets: one black, one white, and one zebra-stripy (just like the one Hannah wants to buy) to control for everything except the coat colour. A team of grad students was sent into the fields to stand there and count fly landings for hours on end. Their graph says it all – there was a huge difference when the horses were dressed up like zebras except on their heads, which were not covered with the stripy fabric.

These flying pests are looking for their next snack based, in part, on a specific property of the light when it bounces off a surface, whether it’s water, a blade of grass, or a zebra-striped sticky mannequin out standing in its field. Light that bounces off dark surfaces like a black stallion is highly polarized, which attracts the flies, whereas the light reflected from white ponies is hardly polarized at all. The mixture of highly polarized and not polarized light from the zebra stripes seems to be the cause of all the confusion.

(Hannah’s horse (Ella), on the left, looking super suave in her new flysheet)

So, science wins and Hannah gets a zebra-print flysheet. A centuries old mystery is solved and it’s not at all about camouflage as Rudyard Kipling would have had us believe all those years ago:

Zebra to The Ethiopian and the Leopard, from inside some little thorn bushes where the sunlight fell all stripy: “And where is your breakfast?” But all they could see was stripy shadows in the forest. (in How The Leopard Got His Spots, Just So Stories, Rudyard Kipling, 1902)

References:

Benefits of zebra stripes: behaviour of tabanid flies around zebras and horses, Tim Caro et al, PLoS ONE 14(2): e0210831 (2019) https://doi.org/10.1371/journal.pone.0210831

Striped bodypainting protects against horseflies, Gábor Horváth et al, R. Soc. Open Sci. (2019) 6: 181325 http://dx.doi.org/10.1098/rsos.181325

Stripes disrupt odour attractiveness to biting horseflies: Battle between ammonia, CO2, and colour pattern for dominance in the sensory systems of host-seeking tabanids, Miklós Blahó et al, Physiology & Behavior (2013) 119 168 – 174 https://doi.org/10.1016/j.physbeh.2013.06.013

Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: an advantage of zebra stripes, Ádám Egri et al, Journal of Experimental Biology (2012) 215 736 – 745 https://doi.org/10.1242/jeb.065540

This Is Why …it’s good to be hard-headed, if you’re a woodpecker

The soundtrack to my walk in the woods last weekend was incredible. The forest was alive with creatures big and small, busy with the tasks of a new season: the spring peepers were cheerfully peeping, the partridges were drumming on hollow logs, tom turkeys were gobbling at full throat. And, above it all, the incredibly loud bursts of hammering from pileated woodpeckers carried through the treetops.

When I stopped to listen, I was struck by the frequency and the volume of this hammering. A pileated woodpecker can hit a tree up to 20 times a second, experiencing accelerations greater than 1000g! (For comparison, humans pass out if we experience anything greater than about 5g.) How does this little creature bash its head against a tree trunk repeatedly, with such force, without sustaining significant brain damage? I’m not the first to ask this question – Philip May and colleagues wondered “why the countryside is not littered with dazed and dying woodpeckers” back in 1976 in an article published in the Lancet.

May and colleagues examined frozen sections of the heads of woodpeckers, comparing them with that of a toucan, a similar-sized bird that doesn’t exhibit headbanging (unless at a Metallica concert). In the woodpecker’s noggin, there is little space between the skull and the brain so, unlike toucans, the woodpecker brain won’t slosh around with sudden motion and slam into the inside of the skull. Also, their skull is made up of dense and spongy bone, especially right at the front. The toucan’s skull bone is “light, almost frothy” in comparison.

The woodpecker’s lower jaw muscles were observed to be more powerful than those in the toucan, suggesting that they play a role in absorbing and distributing shocks, like a boxer tensing up to protect against an opponent’s blow. Perhaps most unique, however, is the woodpecker’s tongue. The base runs from the floor of the mouth to the back of the head, then up and over the top, ending at the front at the right nostril (the red line in the drawing from Jimfbleak here). May and colleagues suggested that this is a muscular protective sling to minimize motion during hammering.

Image by Jimfbleak CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=55897150

The story doesn’t end with that Lancet paper in 1976. Others have noted that there is a thick eyelid that closes just before the woodpecker strikes, both to protect from flying debris but also to keep the bird’s eyeballs from “popping out of its head” (Schwab in the British Journal of Ophthalmology, 2002). A lovely 2006 paper from L. J. Gibson in the Journal of Zoology explores the role of the size of the brain on its likelihood of injury, concluding that the smaller brain corresponds to a lower mass to surface area, meaning that the impact force is spread over a relatively large region.

Woodpecker gif from giphy.com: https://gph.is/2k0Do4Q

More recently, function studies have added to the work done to date on the unique structures observed. Jung and colleagues reported on the mechanical function of the woodpecker’s skull in a 2019 article in Advanced Theory and Simulation. As part of their investigations, Jung’s team built a tower in which they repeatedly dropped their 3D printed woodpecker skulls, beak first, onto a metal plate to observe the effects. They concluded that the main stress wave from impact at the beak travels through the lower jaw towards the neck and spine, away from the brain cavity – a built-in natural stress deflector.

And scientific advancement marches on! From the structural analysis of May and colleagues in 1976 to functional studies by Jung and team in 2019, we are still learning how these birds can subject themselves to such trauma, seemingly without adverse consequences. Maybe some day the brains of athletes will be protected in contact sports with woodpecker-skull-inspired helmets and collars.

Figure 1 from the 2016 Br J SportsMed article cited below, CC BY-NC 4.0, https://bjsm.bmj.com/content/50/20/1276.full

References:

P. R. May et al, 1976 Lancet pgs 454-455

I. R. Schwab 2002 Br. J. Ophthalmol. 86 pg 843 https://bjo.bmj.com/content/86/8/843.short

L. J. Gibson 2006 Journal of Zoology 270 pgs 462-465

J-Y Jung et al, 2019 Adv. Theory Simul. 2 DOI: 10.1002/adts.201800152

G. D. Myer et al, 2016 British Journal of Sports Medicine 50 pgs 1276–1285 https://bjsm.bmj.com/content/50/20/1276.full

This Is Why … physics leads to love for western grebes

(Photo by Keneva Photography)

This elaborate courting display is known as rushing, a mating ritual that is unique to the western and Clark’s grebes (Aechmophorus occidentalis and Aechmophorus clarkii). In showing off for nearby potential mates, grebes in twos and threes run side-by-side across the water for 10 to 20 metres at a time, which is a pretty impressive feat for creatures weighing one to two kilograms. How do they accomplish it?

It turns out that part of the answer is: their feet! The grebe is, by far, the largest animal with this water-walking ability. They need to generate a significant upward push to get above the water and to stay there for 5 to 10 seconds at a time. They always hold their wings rigidly behind them, lifted but not opened, which means that the wings are not contributing significantly to their defiance of gravity here. Instead, their uniquely structured feet are the secret to their success.

The three-lobed digits on grebe feet

Grebe feet have three lobed digits; they look a bit like a piece of an oak leaf. When the grebes slam their feet down on the water surface, the lobes are spread out to maximize the contact area to push against. But, when they pull their feet out again to take the next step, the unique anatomy of the foot and the sideways sweep motion they use are both theorized to minimize the drag from the water. They also slam their feet down with incredibly high velocity, which maximizes the upward push from the surface. If this wasn’t enough, there is one additional key ingredient: grebes can dash across the water taking steps at a rate of 15 to 20 every second! Every step provides upward force, so more steps per second means a greater overall upward push during their sprint.

High step rate, high impact velocity, and fancy folding feet translate into a boisterous and conspicuous display that attracts a lot of attention during the breeding season. The modern dating world is a tough go for us humans, it’s true, but think of all the carefully executed physics that goes into a grebe finding a mate!

Rushing ritual video – https://youtu.be/XQPljqjYNeY

References:

The pair-formation displays of the western grebe, G. L. Nuechterlein and R. W. Storer 1982 The Condor (Journal of the Cooper Ornithological Society) 84 350 – 369 https://www.jstor.org/stable/1367437

Western and Clark’s grebes use novel strategies for running on water, G. T. Clifton, T. L. Hedrick, A. A. Biewener 2015 Journal of Experimental Biology 218 1235 – 1243 https://jeb.biologists.org/content/218/8/1235.long

This is Why … snails are brilliant engineers!

I really shouldn’t be so discriminatory here. All gastropods (the class name for snails and slugs) are brilliant engineers. First of all, they grow their own home; a pretty impressive feat. But that’s a topic for another day … this story is about the incredible properties of their slime.

Snail slime does two jobs: it allows the snail to crawl across a surface, but also helps the little creature stick to that surface. This adhesive role is especially important for marine gastropods, otherwise they’d be constantly shoved around by water currents and swirling vegetation. But, when you think about it, these two functions (movement and adhesion) seem completely incompatible. How does a snail make slime that keeps it stuck to a rock AND allows it to wiggle around to find food?

Back in the 1980s, some clever biologists conducted a series of experiments to find out. They designed and built ingenious devices to test what happens to snail slime when different amounts of push are applied across the surface of a very thin layer, “under conditions as closely as possible approximating those under a crawling slug”. What they discovered is that these creatures generate a truly unique substance: as you push harder on the slime, it becomes runnier. When you stop pushing, it ‘heals’ and returns to something thicker. With very small pushes, the slime acts like a stretchy solid that snaps back into place, like gelatin, keeping the snail attached to the surface. With more sustained, stronger pushes, the slime acts as a runny liquid, like warmed honey, making it easier for the snail to move across the surface.

Brilliant, right? So, the next question is: How? What happens to the slime to change its runniness this dramatically? Well, for that we skip forward almost 40 years to a study by a group of engineers in China, published in 2018. This team collected mucus from snails crawling across smooth glass plates at angles ranging from flat on the lab-bench to completely vertical. As the angle increased, the structure of the slime changed significantly. The slime from the flat plate was made up of tiny little nanoparticles distributed more or less uniformly. The slime from a plate at 45⁰ showed the nanoparticles starting to clump up into microspheres and the slime from the vertical plate was thick with fibres formed from globs of microspheres attaching together. Nanoparticles – runny slime. Microparticles – less runny slime. Fibres – almost gel-like slime. This team is now working on making fibres based on their results for biomedical applications.

Want to make some ‘anti-slime’ at home? We usually call this Goop or Oobleck – 2 parts corn starch to 1 part water (plus food colour if you’d like). When you push gently it behaves like a liquid. When you hit it hard, it feels more like a solid. Squeeze some into a ball in your hand and throw it to a friend – solid in your hand, drippy and runny in the air, solid again when your friend catches it! The exact opposite of what a snail needs to stick to the surface and move around, but a little bit of fun for an afternoon during physical distancing.

(Oobleck gif from Giphy: https://gph.is/1Qm2Kmc)

References:

The physical properties of the pedal mucus of terrestrial slug, Ariolimax Columbianus; M. W. Denny & J. Gosline; Journal of Experimental Biology 1980 88 375-393 (https://jeb.biologists.org/content/88/1/375)

Controlled self-assembly of glycoprotein complex in snail mucus from lubricating liquid to elastic fiber; T. Zhong et al; Royal Society of Chemistry Advances 2018 8 13806-13812 (https://pubs.rsc.org/en/content/articlelanding/2018/ra/c8ra01439f#!divAbstract)

This Is Why … Mother Nature is a physics genius!

Have you ever found yourself lying on the lawn on a summer day, absentmindedly examining the dandelions there? The cheerful yellow flowers, bowing their heads under the weight of bumblebees feeding on their nectar. A nearby collection that has gone to seed, with dense pods at the base of long, delicate stems and a bundle of bristles at the top, called the pappus. You pick one and blow while making a wish, and the tiny little cloud of filaments scatter, potentially travelling over 100 km in warm, dry air.

Mara blowing cattail seeds into the wind (dandelions are not yet available in this part of the world!)

Wait – 100 km? Just drifting on air currents? Science helps us to understand how the intricately delicate design of the pappus is the perfect aerodynamic structure for making sure the seeds get spread as far as possible on the wind, giving rise to the incredible success of this plant in the western world.  For years it was believed that the pappus acts like a parachute, increasing the drag on the seed to keep it afloat for longer than it would without this structure attached. But recent studies have demonstrated that drag alone is not enough, and the precise design of 100 to 110 fine hairs per seed is critical to these long flights.

(Mara is substituting cattail seeds here for dandelions, given the season!)

In 2018, a team in Scotland reported beautiful experimental results showing that the airflow through these filaments creates swirling rings of air, called vortices, behind the seed as it travels. This creates a region of low pressure behind the pappus, increasing the lift and allowing the structure to stay aloft for incredible distances, way further than if the seed was attached to a more conventional parachute-like design. The following year, scientists in Switzerland mathematically modeled the airflow through the filaments of the pappus, confirming these experimental findings.  They even found that the optimal number of hairs on the pappus for maximum flight stability is 100, precisely the typical number found on every dandelion seed in your lawn. Mother Nature is a brilliant physicist!

More details:

Experimental work: https://www.nature.com/articles/s41586-018-0604-2

Theoretical work: https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.4.071901

This Is Why … skipping stones is anything but child’s play!

A perfect July morning. You quietly prepare a cup of coffee and slip out of the cottage to head down to the lake. The surface is so still – the treeline on the far shore reflected in the surface like nature’s Rorschach test. That perfect surface calls out for a little physics fun, so you go in search of the perfect skipping stone: not too big; not too small; smooth and flat and round. With much experimentation over the years, you’ve got it down to an art – the perfect launch speed, the perfect launch angle, and just enough spin – the stone skitters across the surface leaving a satisfying trail of ripples in its path.

“Skipping Stones” by zoxcleb is licensed under CC BY-SA 2.0

Here’s the incredible thing – there’s a heck of a lot of physics built into a successful stone skip. In the early 2000’s a group of scientists led by Lyderic Bocquet at the French National Centre for Scientific Research (CNRS) took a rigorous approach to understanding what goes into the perfect throw. You might have a feel for the ideal parameters, but this team can give you pretty precise numbers!

There are four key ingredients for a successful stone skip:

1)      Speed (higher initial speed = longer path before sinking, greater # of bounces possible)

2)      Spin rate (faster spin rate = greater stability, greater chance of bouncing repeatedly)

3)      Angle of the stone with respect to the water surface (ideally a little bit bigger than zero, called the tilt angle, given the symbol alpha)

4)      Angle of the stone’s direction of motion when it hits the surface (ideally moving mostly parallel to the water and a little bit down, called the impact angle, given the symbol beta)

It might seem a little confusing, but the two angles here are not the same thing. You can physically see the tilt angle, but it’s harder to picture the impact angle, beta. If the stone is travelling horizontally across the water, beta = 0 and if the stone is dropped straight into the water, beta = 90⁰, regardless of how the stone is physically oriented.

Getting stones to skip depends on the combination of all these variables – it’s actually pretty crazy that we can do it!

The French team conducted exhaustive experiments with their aluminium “stone” with radius of 2.5 cm, and thickness of 2.75 mm. They found that spins of about 40 rotations per second and higher resulted in greater stability for the stone to maintain its tilt angle as it bounced. They also found that a tilt of about 20 degrees was a ‘magic’ value, since it seemed to result in skipping at the lowest possible speed, as well as working well for a wide range of beta values. So maybe ‘magic’ here really means ‘more forgiving’.

The challenge with achieving lots of bounces and a long run is that the stone loses a bit of energy to the water with each interaction. The flatter the tilt angle, the less energy it transfers to the water as it bounces – much like a canoe paddle slicing through with its blade parallel to the surface rather than straight up and down in the water. So, a flatter tilt angle should go further and bounce more. The trouble with this trajectory is that successive bounces don’t go as high above the surface, so a little bit of chop in the water and the record-winning run is over.

88 skips … current World Record!

There is a lovely paper by Charles Babbs in The Physics Teacher that derives a simplified model of the mechanics of skipping stones, but without the complications of considering spin.  Naturally I had to investigate the math … here’s what happens when you change the tilt angle from 10 to 25 degrees while keeping everything else the same:

Each stone follows the same black curve to the first bounce, but then things change dramatically after that. The steeper the tilt angle, the more energy it loses with each bounce and the more steeply it bounces out again, as seen in the lab by Bocquet and crew. The flattest tilt angle travelled the furthest with the most bounces – a total of 14 complete hops (purply-pink curve) before petering out in pitty-pat (yes, that is the technical term!).

Bottom line? Like so many other things, there is tons of cool physics behind the simple art of stone skipping. Keep experimenting!

Further details? Here are the papers I’ve mentioned:

Charles Babbs paper in The Physics Teacher: https://aapt.scitation.org/doi/10.1119/1.5098910

French team papers:

https://aapt.scitation.org/doi/10.1119/1.1519232

https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/skipping-stones/20F788FE0082904112537C46F0CC5A2A

https://www.nature.com/articles/427029a

This Is Why … foodies focus on foil’s physics

(Photo by Lum3n.com from Pexels)

As a physicist, I don’t really get asked for professional advice all that frequently. Our Carpenter Buddy was super helpful with our deck construction project (Thanks Drew!) and our MD Pal gets asked about questionable moles (and more exotic things) all the time. But it’s not often that a social gathering sees someone grappling with the finer points of the Laws of Thermodynamics.

When my scientific expertise is called upon, it’s usually because someone’s child has asked a great “but why?” question that Mum or Dad isn’t entirely sure how to answer. My absolute favourite questions are the ones that make me say: “hmmm … I don’t know! Let’s find out together!” Here’s the most recent one, courtesy of my almost-twelve-year-old nephew, Cameron Redmond. Foodie Cam wants to know: why is foil shinier on one side compared to the other? And, does it matter?

Now the first question is pretty straightforward to answer – it’s shinier on one side compared to the other because of how it’s made. Foil is made from sheets of aluminum that are sent through industrial-sized rollers to squish it nice and thin. With each pass through these rollers, the foil gets thinner and more delicate – a bit like sending your fresh pasta dough through the press to get it nice and thin.


“Making pasta” by Kim Siever is licensed under CC PDM 1.0 

For the final squish through the rollers, the aluminum sheet is folded over on itself, doubled up to make it stronger. The top and bottom surfaces, against the rollers, come out extra shiny. The inside surfaces that are pressed against each other, not so much. When the final sheet is unfolded, you have one slightly shinier surface and one that is a little dull looking.

Now, for the second part of Cam’s question – does it matter? Well, the answer to that is: it depends. If you’re going to use this foil to wrap up a potato for baking in your oven or in the coals of a campfire, then no. In both these scenarios, the potato heats up by a process called convection: the surrounding hot air transfers heat into the potato. The temperature climbs at a rate that has nothing to do with whether your spud is wrapped in a super shiny jacket, a less shiny jacket, or is au naturel – it mostly depends on how big the potato is and the temperature difference between the surrounding air and the spud.

But, if you don’t happen to have easy access to a regular oven or firewood, and you are just craving a baked potato, then the difference between the shiny and dull side of the foil could be a factor as you build your solar oven.

Solar ovens are fantastic devices for harnessing the heat from the Sun to cook. The most important feature is being able to collect a lot of the Sun’s energy and concentrate it into the small space where the food is located. Using the shiny (more reflective) side of aluminum foil, you can direct more sunlight into this central space and get your baked potato ready more quickly!

For more construction details: some great instructions can be found here from The Children’s Science Center in Virginia.

So, for everyday cooking, shiny or dull doesn’t really matter. But, it does matter if you’re building a solar oven. And, if you’re making a foil hat to block your nemesis from reading your mind, you should definitely keep the shiny side out. You’d look just plain silly otherwise!

From: http://on.cc.com/2xU0Gh4

This Is Why … equestrians trust their lives to physics!

It’s ridiculously early on a cold January morning. I’m shuffling my feet to keep warm and to burn off some of my nervous energy. As I hold my breath, my teenage daughter trusts her life to her horse and her training, as they dart around the jumper ring at top speed. The goal is to finish the course of about a dozen jumps with the fastest time, leaving all the rails in place. I know that if she also trusts the physics, she has a good chance at a clean round.

Physics? Yup.

When learning to jump, her (amazing!) coach instilled in her the golden rule: your takeoff point should be the same distance from the base as the rail is above the ground. In physics terminology, her coach was telling her the golden rule of projectile motion – your projectile (i.e. your horse) will go the furthest before landing if you launch at 45° to the horizontal, no matter what speed you are travelling when you take off.

The speed matters, of course, because it will affect how far you go before landing, as well as how high you go at the top of your flight over the jump. But, as golden rules go, it’s an easy one to remember and is solidly based in physics principles.

Is a horse going over a jump really a projectile like an inanimate football? To check this, I loaded a video of Hannah and Ella into some pretty cool (and free) software to analyze the motion of objects (https://physlets.org/tracker/), to see what it looks like from a physicist’s perspective. It turns out that when we plot Ella’s vertical position as a function of horizontal position, it nicely tracks a curve we call a parabola – which is EXACTLY what you expect for any projectile (football, golf ball, tennis ball, flying squirrel or jumping horse).

Tracking the vertical and horizontal positions of Hannah and Ella as they go over a jump.

As you can see in this screenshot from the associated video, our pair took off at an angle of about 35° from the horizontal. With some great helpers, I measured the distance from her launch point to the base of the jump to be about 55 cm and the distance from the base to her landing point at about 60 cm. This matches the graph above from the video analysis, which shows that their jump was not exactly symmetric over the rail (the x = 0 position) – coming in a little closer to the base than where they landed – but pretty good!

Screenshot from video of jumping, showing the takeoff angle of approx. 35 degrees
Coach Cindy (left) at the landing spot and little sister Mara (right) at the take-off spot

Let’s assume then that we can apply equations of projectile motion that we use in first-year physics to Ella’s path. Since we know the launch angle of 35° and the total distance from launch to landing of 115 cm, we can figure out that the launch speed must have been about 3.5 m/s (~12 km/h), which is consistent with a steady canter pace. If Hannah and Ella want to jump higher and/or further before landing, that launch speed needs to go up, but the golden rule of taking off as far from the jump as it is high still applies for maximum distance for their efforts.

Slow motion video of Hannah and Ella showing takeoff and landing.

Now if we could just get horsey folk to call horizontal rails “horizontal” instead of “vertical”, we’d all be talking the same language!

This Is Why … it stings when you ski through a blast of fake snow

My little Jozo Weider racer, in her first ever away race earlier this season. Photo by Rob Tankovich, Head Coach, U10 program

It’s coming to the end of ski season in this part of the world, which makes at least two members of my household incredibly sad. With the forecast for the week ahead projecting several days with highs above zero degrees Celsius, the local area ski hills will be making as much artificial snow as they can in the evenings when it gets colder. Ideal temperatures for making snow is about ‒5 to ‒10⁰C (cold enough to produce lots of powder, but not too cold that the water freezes in the hose before getting to the snow gun). Humidity is also a factor …. snowmaking needs less than about -2⁰C and 50% humidity to really work. A bit of natural snow falling is also helpful.

Water and high pressure air are pushed through the nozzles of the snow gun at high speed. The air expands as it comes out of the nozzle, dropping in temperature, quickly turning the fine water droplets into tiny ice crystals. These serve as seeds or nucleation points for more water droplets to accumulate and freeze, forming snow as they fall to the ground. The hang time is only a few seconds, so conditions have to be just right for the end result to be skiable. There definitely isn’t enough time to form the classic and elaborate flakes we usually picture, so the snow that falls is icier and more pellet-like than the stuff from the heavens and boy, does it sting a little when you ski through the blast from the guns! Once decent piles (called “whales”) have accumulated, groomers move it around for optimal coverage.

“Whales” forming with snowmaking at full blast (“IMG_8995” by V31S70 is licensed under CC BY 2.0)

Snowmaking was first discovered by a team of Canadian scientists in the 1940s, led by Dr. Ray Ringer. The team was attempting to study icing on jet engines, but they found that they were very good at filling their wind tunnel with snow instead of ice when they sprayed fine water droplets into the air. Their scientific paper formed the basis of the US patent filed in by Tey Manufacturing (Milford, Connecticut) in 1954. The technology has evolved considerably since the 1950s.

In addition to state-of-the-art snowmaking, some resorts in the Alps have been attempting “snow farming” in recent years, as the ski industry continues to wrestle with climate change and the impact on their bottom line. Using the great thermal insulating properties of sawdust over the snow, as well as reflective tarps, resorts are finding that they can start their season a little earlier the following year if they can keep it all from melting during the warmer off-season. For example, Davos in Switzerland has been using sawdust coverings, estimating that they can save 70 to 80% of their snow volume this way. Would this work in Ontario? Not likely – Davos has much cooler summers than we do, with typical peak summer highs of only about 20⁰C.

Snowmaking isn’t just about getting a few more runs on the slopes early/late in the season – a team from the Netherlands, led by renowned glaciologist Hans Oerlemans, has been experimenting with using snow cannons to protect glaciers in the Alps that are melting rapidly due to climate change.

In October 2019, Oerlemans was awarded 2 million Swiss francs from the Swiss Innovation Agency to explore his idea of creating a blanket of artificial snow on the Morteratsch glacier as a means of protecting it from further melt. The team is looking at using gravity feed of water from high altitude glacial lakes to minimize energy costs, but there is a lot of work to do. The hope is that their solution could extend beyond the lucrative ski/tourism industry to communities in developing nations, such as Tibet and India, that rely on glacier melt for crops.

CN Advertisement – circa 1950s

Will snowmaking be the way to slow global glacier melt due to climate change on a large scale? Absolutely not. But it is an interesting application of an accidental 1940s Canadian discovery – I mean, you knew there had to be Canadians involved from the beginning, eh?