omenti

an almost lost word from the dictionary

Reading an obscure paper from the 1880s a word stopped me - apricity.  It seemed like I had come across it before and there were hints from the context, but it was time for the OED.¹  I pulled out the first volume of my old compact edition - the one with the magnifying glass - and found it.  An obscure word dating to 1623 meaning the warmth of the Sun in the Winter.

 

The warmth of a bright Sun in on a clear cold Winter day.  That's something that captures most of us know - the radiant heat of the Sun isn't isn't perturbed by the cold air and can be quite comfortable.  Then it hit me I heard the word in a John McPhee lecture in Princeton.² A few decades had passed since he wrote Coming into the Country, but it was about three Alaskas including a look at the Winter.  A perfect word for some of the days.

 

A day of apricity can make snow melt in subzero air temperatures on  Southern-facing roofs only to freeze into beautifully clear long icicles at the edge.  This type of ice formation is often free of bubbles producing beautifully clear ice.  If you have wide enough icicles you might try making an ice lens and starting a fire.

 

Such days are made for outdoor recreation if there isn't any wind.  Perhaps more importantly the basic principle - heat transfer by radiation - can keep heating expenses down.  Heating and moving air to fill rooms is enormously inefficient. If you aren't moving around much you might try a small radiant heater and point it at the area where you are. Heat what you need to heat with infrared light. Direct sunlight is the same...  sit in the Sun.  These measures, plus wearing warm indoor clothing and being somewhat active lets you get away with low thermostat settings.  And be on the lookout for aprocity as that can give a big psychological boost!

 

Another Winter word I like is tingilinde. It's a constructed word based on J.R.R. Tolkien's elfin language Quenya meaning the sparkle of the starlight reflecting on the snow on a dark moonless Winter night.  Such sights could be spectacular in Montana away from town when it was really cold and a bit of new snow had fallen as tiny ice crystals. Another great spot is Yellowstone .. super cold air forms the right kind of ice crystal snow near the hot springs and geysers.   Once it was magical - the cold starlight reflecting from millions of tiny diamonds along with the greens and reds of a bright aurora dancing overhead.   On such nights you don't notice that it's really cold.

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¹ The Compact Edition of the Oxford English Dictionary is the 1928 edition.  Devilishly small print that requires a magnifying glass, but the real OED and only about $80 (still a lot back then!) rather than the fortune the full dictionary went for.  There's a lovely bit of historical fiction on the dictionary and the people who made it happen:  The Dictionary of Lost Words by Pip Williams.  It's set in the time and place with many of the characters, but focuses on what was left out..  those who weren't white, male and of a certain class.  Recommended!

² McPhee is a great writer - a master of the creative non-fiction genre.   

 

 

 

digging in a bit deeper

He would see something familiar in a cloud, the habit of a tree,  or a splatter of mud and use it as inspiration for one of his stories.  Lloyd loved stories.  Growing up, his would make up new stories to tell each other twice a month and, as an adult, he continued the tradition with his own family and the neighborhood kids.  I was one one of those kids. 

 

One night both of our families were camped near Two Medicine Lake on a spectacularly clear and dark June night.  The mountains cut pitch black outlines into the starry sky with new stars bursting into view as the Earth rotated. So many stars were visible it was difficult to find some of the constellations so Lloyd made up some of his own and started into his storytelling.  But two constellations survived - the Big and Little Dippers.  They were so well known to everyone that it was difficult seeing something else.   My contribution to the evening was pointing out some dark patches in the Milky Way. Like the mountains that seemed to be eating the sky and one looked like a galloping horse - enough to launch Lloyd on one of his ten minute excursions into fantasy.

 

Pareidolia is something familiar in otherwise unrelated objects.  It's seeing the face on the Moon or a bunny rabbit in a cloud.  It's a type of apophenia - our tendency to look for patterns in information.  Sometimes the patterns are there, often they're not.  The trick is to take a critical empirical look at the underlying information.  Exactly what is it? How was it measured and what steps were used to interpret it?  (this is where machine learning can fail  .. it's not just bad data sets).

 

Let's go back to the constellations - Ursa Major, the Big Dipper, in particular. Early on we learn that, with the help of culture, we're just finding familiar patterns as we connect the dots.  Stars are usually at different distances and brightnesses.  We're giving up the third dimension.  Nothing to see here .. or is there?

 

For years I considered the constellations to be nothing more than useful human constructions for finding one's way around the sky.  Ursa Major turns out to be special when you dig a bit deeper.  If you ignore Alkaid, the end of the handle, and Dubhe, the furthest point on the bucket, the remaining stars are all just a bit more than 80 light-years from Earth.   They also have the same proper motion - they're moving in the same direction at about the same speed.  Use a telescope and look at the distance and proper motion of dimmer stars you find over fifty that make up a physical cluster.  Spectroscopically they're very similar.  It looks like they were formed from the same dense cloud of gas about a half billion years ago - just after the Cambrian explosion on Earth.  With the exception of Alkaid and Dubhe they've moved in a slowly expanding formation and will continue along their way for some time 

 

And for years I thought the grouping must be nothing more than a human construct. A more critical look exposes a richer story.

 

 

 

 

what's in a name?

Surrounded by dramatic peaks on a narrow road etched into the side of the mountains you drop into forested area that continues into a string of foothills.  It's clear and you wish you were on your bike this time around.  The trees thin out and suddenly it's upon you.  You're at the summit of the last foothill and the expanse of the prairie opens up ahead.  Off in the distance is a short mountain range, but mostly it's prairie and you need to catch your breath.

 

Oceans and mountains have their appeal, but so does the prairie.  I suspect Montana Jeri and Alberta Jheri know this too. More than a few people from the area are taken by the outdoors. You find a number of artists, photographers, as well as people who are taken to learn about their surroundings.  I feel hard for the sky and have yet to recover.

 

The area is positioned such that auroras aren't uncommon during solar maximums.  Alberta and Saskatchewan have groups of serious amateur aurora watchers.   About ten years ago they realized something was different.  Something more frequent than garden variety auroras with a different color (they'd say colour) and shape.  Early spectrographic measurements revealed it was a thermal emission rather than the distinct colors of excited atoms dropping to lower energy levels.  

 

Serious work using satellites and the rich ground-based observations of the Canadian amateurs began around 2016.  It was real and not an aurora.  It needed a name.    One based on a children's movie turned out to be perfect.

 

The backronym Strong Thermal Emission Velocity Enhancement nicely suggests STEVE.

 

 

Much more is known now and the name remains.  The past week has been some beautiful displays along the Canadian Rockies.  I say them as a teenager and then again in my 30s, but didn't realize they weren't auroras.   Cheers to those curious enough to ask the questions.

 

orbits

It's almost Perihelion Day!   I may wish people Happy New Year, but the beginning of a calendar year is artificial, so I celebrate a specific point in our orbit every year.

 

The orbit of the Earth is elliptical. Not terribly so, but enough we're about 5.1 million kilometers closer to the Sun in early January than we are in early July.  The closest point is the perihelion and the furthest, the aphelion.  The exact time of perihelion varies from year to year - this year it's the 4^th of January at 6:52am UT or 1:52am EST.  Californias get to celebrate on the 3^rd.

 

At perihelion the Earth is at its fastest speed in our orbit - 30.29 kilometers per second.  At aphelion, the slowest point, we've slowed by about a kilometer per second.  Given its closeness, the apparent disk of the Sun has about 7% more area at perihelion than it does at aphelion.  That seems to bother people as it's Winter in the Northern Hemisphere.  In fact the Earth is a bit more than 2°C colder at perihelion than at aphelion - an artifact of the distribution of the continents and a bit of physics.

 

There more land in the Northern than the Southern Hemisphere.  Water has a higher heat capacity than land.  Think about a desert.  During the day it can get scorching hot, but it rapidly cools off at night.  The ground doesn't hold heat as well as water.  In July the Northern Hemisphere has long days that allow the land to heat up for longer periods raising the temperature of the air above it and raising the average temperature of the Earth in the process.   In January the Southern Hemisphere is getting the most sunlight, but most of it falls on water, which doesn't heat up as much as the land. 

 

There are some interesting rabbit holes one can get into and much can be learned by studying the positions of bodies in our solar system and people have been doing it for thousands of year.   Some civilizations were very sophisticated in calculating and predicting astronomical events even though their models of the solar system were wrong.  An early computer that makes your jaw drop is the Antikythera mechanism.  People have been studying it for over a century and Scientific American has a fine summary of what's currently known about the device.

 

In 1900 diver Elias Stadiatis, clad in a copper and brass helmet and a heavy canvas suit, emerged from the sea shaking in fear and mumbling about a “heap of dead naked people.” He was among a group of Greek divers from the Eastern Mediterranean island of Symi who were searching for natural sponges. They had sheltered from a violent storm near the tiny island of Antikythera, between Crete and mainland Greece. When the storm subsided, they dived for sponges and chanced on a shipwreck full of Greek treasures—the most significant wreck from the ancient world to have been found up to that point. The “dead naked people” were marble sculptures scattered on the seafloor, along with many other artifacts. Soon after, their discovery prompted the first major underwater archaeological dig in history.

One object recovered from the site, a lump the size of a large dictionary, initially escaped notice amid more exciting finds. Months later, however, at the National Archaeological Museum in Athens, the lump broke apart, revealing bronze precision gearwheels the size of coins. According to historical knowledge at the time, gears like these should not have appeared in ancient Greece, or anywhere else in the world, until many centuries after the shipwreck. The find generated huge controversy.

...

 

A more technical discussion appears in a recent article in Nature (open access)

 

A Model of the Cosmos in the ancient Greek Antikythera Mechanism

Tony Freeth, David Higgon, Aris Dacanalis, Lindsay MacDonald, Myrto Georgakopoulou & Adam Wojcik

The Antikythera Mechanism, an ancient Greek astronomical calculator, has challenged researchers since its discovery in 1901. Now split into 82 fragments, only a third of the original survives, including 30 corroded bronze gearwheels. Microfocus X-ray Computed Tomography (X-ray CT) in 2005 decoded the structure of the rear of the machine but the front remained largely unresolved. X-ray CT also revealed inscriptions describing the motions of the Sun, Moon and all five planets known in antiquity and how they were displayed at the front as an ancient Greek Cosmos. Inscriptions specifying complex planetary periods forced new thinking on the mechanization of this Cosmos, but no previous reconstruction has come close to matching the data. Our discoveries lead to a new model, satisfying and explaining the evidence. Solving this complex 3D puzzle reveals a creation of genius— combining cycles from Babylonian astronomy, mathematics from Plato’s Academy and ancient Greek astronomical theories.

 

Back to now.  Happy Perihelion Day to all of you!

and a comment

I'm  not fond of the idea of the Earth making a circuit every year as, the Earth never comes back to the same spot in any reference frame.  It's roughly close enough for most, but in four dimensional space time it's something of an approximate helix expanding out along the time axis.  You can never go home. Good enough reason to look forward!

 

 

 

 

 

frozen bubbles

minipost

 

Someone asked about the frozen bubbles we made years ago at Stony Brook.  It turns out that bubbles freeze (there's some interesting physics going on) with interesting patterns.¹  I've never tried to photograph them as (a) only about ten percent of my bubbles freeze properly and (b) I'm not a photographer. 

 

The recipe I've used forever is 

200 ml warm water (warm enough to dissolve the rest of the ingredients)

35 ml corn syrup

20 ml dish soap

25 grams (2 tbl white sugar)

a cold calm day or evening with some good lighting.  I generally find temperatures between -15°C and -25° C  best.  One can experiment with the final water temperature as a first step.  If you're really serious you could try a walk-in freezer. (not that I haven't been tempted)

Here's an excellent video on YouTube.

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¹ Here's my hypothesis of what's going on.  A liquid gives off a bit of heat when it freezes - the latent heat of fusion.  Those vibrating water molecules lock into a structure and the energy of the water molecules motion has to go somewhere.  When the bubble lands on a cold surface it begins to freeze at the point of contact. A ring shaped freezing front proceeds up the bubble.  As the region freezes a bit of heat goes to the liquid part of the bubble in the immediate area that hasn't frozen causing a flow of slightly warmed water that moves upwards.  This flow grows and puts stress on the freezing front causing bits of new ice to break off and slide around the still liquid part of the bubble.   If I'm right the illusion that individual freezing zones form is just that - an illusion - and an artifact of the single moving ring.

The corn syrup gives sturdier bubbles.. the white sugar doesn't totally dissolve and gives good nucleation sites for crystal formation.

Of course this is just a guess that would need testing.

 

 

getting to clean enough

It's becoming clear that the SARS-CoV-2 virus will be around for a long time.  We're probably much closer to the beginning than the end.   Hotspots will shift and new variants arise so it makes sense to be ready to mitigate risks as much as possible.  Vaccinating the world should be a high priority along with next generation vaccines, better treatments, testing, high quality masks when the risk is high, etc. etc.  

 

Improving local air quality is low hanging fruit.  To first order that means high quality masks in hotspots along with fresh air.   Room air filtration and circulation can be a powerful tool.  As living animals we exhale carbon dioxide.  In pristine location, say a mountain top in Hawaii, you can measure the baseline concentration. Air is about 420 ppm (parts per million) carbon dioxide - a bit over 0.04%.  Enclosed spaces with people have higher concentrations.  You're breathing some of the air from other people.  If people are the only source, you can calculate the percent of the total air in the room that's exhaled:

        CO₂ concentration (ppm)        % of total air that is exhaled 

                    420                                                  0%

                    600                                                0.5%  

                    800                                                1.0%

                    1000                                              1.5%

                    2400                                               5.0%

 

With these numbers it was believed the risk is low for up to an hour if everyone was wearing a simple cloth mask and one person was infected with the alpha variant with carbon dioxide concentrations as high as 800 ppm.  The delta variant changes the threshold.   Now the one hour number is about 600 ppm with everyone wearing a surgical mask.¹  Of course the probability of an infected person being in the room is low if you're in an area where the infection rate is low.  

 

It would be good to know the concentrations where ever you go:   offices, classrooms, stores, theaters, taxis, airplanes etc.²  Consumer grade carbon dioxide meters can be purchased for $100 to $300.  If you're really interested I can make a recommendation, but I've only used a few.  We'll probably see a rapid improvement as these are going to be essential tools.  Japan is requiring them in many public places and school rooms.³  It's important to have an NDIR sensor (basically it's doing spectroscopy with an infrared laser to measure concentration  - there are many other techniques, but this is the cheapest with enough accuracy and repeatability).  These are accurate to about 50 ppm, so ignore the more exact looking reading and just round up to the next multiple of 50  - if it reads 537 just call it 550.    It takes about two minutes to get a stable reading and you'll want one that stores measurements.  The model I like talks to an iPhone app which gives you a nice chart of the day.   For businesses and schools it's a good way to check if the rooms are getting good airflow.   I saw one schoolroom that exceeded 3000 ppm when students were present. It turned out an air return duct was blocked - a thirty minute fix gave the students clean air again.

 

High carbon dioxide concentrations make people drowsy and sap cognitive abilities.  It hasn't been carefully studied, but readings over 1000 ppm can make you drowsy and perhaps a bit feeble minded.  One Army study suggests 800 ppm should be a warning level.  Half-jokingly I told a superintendent that he could justify the cost of measurement though improved test scores.  It turned out that's what sold him.  Maybe it's a way to upgrade the collective intellectual capacity of an office.  Another benefit is a possible reduction in airborne diseases like the flu.  

 

You can't always open windows and doors to get a solid draft, but HVAC systems can often have their fan settings increased and room vents adjusted. High quality filters can capture viruses along with other particulate like some from a fire.  MERV-13 is a sweet spot for price,  the ability to snare virus sized particles and not requiring more powerful fans.  And you can buy or build portable air cleaners.

 

The hot ticket for rolling your own is a very simple design known as the Corsi-Rosenthal cube.  Here's the public domain diagram we used to build 84 of them for about $5,000  (the cost shown in the drawing doesn't involve much shopping around).  We used the cardboard from the shipping boxes the fans came in.  The shroud is very important.  Square corners disturb the airflow and can drop the unit's efficiency by about a third. A normal sized classroom for 30 to 40 students probably needs two units.  Keep them away from walls, doors,  and openable windows.  The filters will probably last the school year if you turn them off when people aren't in the room.  Most of the classrooms are showing readings under 600 ppm with these and the school's HVAC system fans all on high.  The boxes make a big difference.  Commercial air cleaners with good filters probably make more sense in offices and schools if they want to go long term, but 600 cfpm MERV-13 filters are about $500 and in short supply these days.   Like carbon dioxide meters I suspect we'll see some movement on air filter and fan design. 

 

Some learnings:

Duct tape is frustrating!

Schools have mountains of duct tape.

Eighth graders are the perfect people to enlist if you want to build a lot of them.  Eighth grade girls if you want them to be semi-presentable.

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¹ These are rule of thumb numbers based on empirical evidence.  But it's complex with many confounding factors. 

² A closed car can be spectacularly high. I sat in my car for fifteen minutes with one other person and recorded 3800 ppm!  You can drop this by opening the windows.  Opening them diagonally makes a lot of sense for creating airflow.  Airliners have good general circulation, but a given row can be bad.  A flight is probably much safer than a half hour Uber ride if the driver has the windows up.

³ People are already taking measurements in gyms, restaurants, etc and putting them online with locations and business names. It's ad hoc and not very standardized, but there are over 100 locations in NYC the last time I checked.  It makes much more sense for a business to do their air handling homework and post numbers in their establishment as well as their website.  Hopefully at some point a respectable aggregator will step in.

 

                                      

dancing the parabola

from Radiolab on the history American Football (fans may want to listen)

excerpted from the show:

 

JAD: Which gets us to that game. November 23rd, 1907, Carlisle plays the University of Chicago. Last game of the season. We're in Chicago. And the Chicago team is arguably the best in the nation.

ROBERT: The best. I don't think it's even arguable.

JAD: Well, Carlisle's good at this point, though.

ROBERT: Yeah. But Chicago's like Stagg Field, whoa!

JAD: And there are 27,000 people in the stands.

SALLY JENKINS: Well, what happened was the Chicago players had decided to try to defeat Carlisle's innovative forward passing by just knocking the crap out of their receivers every time they came off the line of scrimmage.

JAD: And so Carlisle's greatest receiver, Albert Exendine, our guy, had been stymied the entire game, because the minute the ball was snapped the Chicago players would ...

SALLY JENKINS: Hit him and try to throw him down or knock him out of bounds. So Pop Warner said to Exendine, here's what we're gonna do. Next time they hit you out of bounds, sneak around the bench and get back on the field.

JAD: By some accounts, this was Exendine's idea. But whoever thought of it, on the next play Albert Exendine as expected ends up out of bounds, but he keeps running.

SALLY JENKINS: He runs around the back of the bench.

JAD: Runs around the spectators, maybe around the band.

SALLY JENKINS: And comes back on the field.

JAD: Right at that moment ...

SALLY JENKINS: Hauser, the quarterback of Carlisle ...

JAD: Lets loose a vicious spiral.

JAD: Can I have you read something?

SALLY JENKINS: Sure.

JAD: Hold on.

JAD: This is Sally's description of that moment from her book The Real All Americans.

SALLY JENKINS: For a moment, it was a frozen scene in a staged drama. The ball hung in the air, a tantalizing possibility. Could Exendine reach it? Would he catch it or drop it? Defenders wheeled and stared down field. Spectators watching from the stands found that the breath had died in their collective throats. The spiraling ball seemed to defy physics. What made it stay up? When would it come down? In that long moment, 27,000 spectators mashed together on benches and crammed on platforms may have felt their loyalty to the home team evaporate in the grip of a powerful new emotion. They may have noticed something they never had before: that a ball traveling through space traces a profoundly elegant path. They may have realized something else. That it was beautiful. The ball struck its human target. Exendine caught the pass all alone and trotted over the Chicago goal line. The stadium exploded in sound and motion. It was the game breaker. The rest was just anti-climax. The final score was 18 to 4 for Carlisle. But the very next year, the Ivy League passes a rule that you can't leave the field and then come back on to it.

JAD: Oh, that's where that rule came from.

SALLY JENKINS: Yes. That's where that rule comes from.

JAD: And I've got to say that that description of the ball in the air is -- is timeless, in a way.

ROBERT: Beautiful.

JAD: That's exactly why football is still beautiful at times.

SALLY JENKINS: That's -- that's when -- Carlisle in 1907 is when American football becomes the sport that you watch today.

 

The parabolic path of a ball in flight.  For many there's something profound and even beautiful about the path.  Physics dictates it.  Throw something in the presence of gravity and you get a parabolic trajectory.  Well - almost parabolic.  Air resistance slows the projectile and change the path anywhere from a little to a lot and some things crafty humans have done can further deviate the path - and sometimes the perception of the path - making sport and art even more interesting.   It's something to watch for as the Olympics unfolds.

 

Jumping is a parabolic motion.  A person launches themselves into the air and their center of mass traces out a parabolic path.  It happens in the long jump, high jump, pole vault, dance, basketball, volleyball and much more.   Athletes often change their shape and orientation around their center of mass to achieve a goal.  A high jumper folds their body around a bar even though their center of gravity passes beneath (the Fosbury Flop).  A ballet dancer appears to hang in the air when executing a grand jeté while their center of mass traces a parabola.   The same illusion of hang time appears in basketball and volleyball.  And gymnasts are masters of dancing their bodies around the parabolas they've created fractions of a second earlier. 

 

Dimples on a golf ball minimize drag and have a large impact on range.  Spin on a golf ball creates a force known as the Magnus effect that changes the ball's path a bit. Backspin, for example, creates lift.  This effect has an impact on most other sport balls giving the athlete some control on the deviation from an expected parabolic path.  In sports like soccer, table tennis and volleyball the effect is pronounced.

 

Some balls pass through interesting speed ranges where the drag on a ball can change dramatically on different parts of the ball adding a bit of chaos to the parabola. The screwball is a good example.  These unpredictable paths are often difficult to master, but have become weaponized in a few other sports than baseball.   

 

I've written about most of these effects in more detail, but it's fun to watch for these deviations from the expected parabolic trajectories.  I started with American football and should mention the spiral.

 

In many sports spin is used to make a ball's path less predictable while in American football it's used to make the path more predictable and easier to catch.  The difference is the odd shape of the ball.  Drag from air resistance depends on the football's orientation.  This is fine when the ball is kicked. The fact it's tumbling makes the path a bit more unpredictable to the opposing team.  

 

A spiral pass is a different matter.   Here the quarterback puts spin on the ball as it's thrown. The higher the spin, the more stable the football.  This turns the ball into a gyroscope of sorts.  If the ball is thrown pointed slightly up, for example, it will retain that orientation throughout its flight.  The coefficient of drag remains constant and deviation from the expected parabola will be constant.  That and the ball won't be tumbling when the receiver catches it. 

 

There is a tradeoff.  A quarterback has a finite amount of energy that can be transferred to the ball.  Putting spin on the ball reduces how fast the ball can be thrown.  Six hundred revolutions per minute is something of a minimal sweet spot.  The ball is stable at that spin rate and it doesn't reduce range as much as a faster spin would.  There's also another constant force from the direction of spin that makes the ball curve a bit to the right or left depending on the handedness of the quarterback, but that's another discussion and something quarterbacks compensate for.

 

beyond the swimming obstacle course and horse long jumping

A pre-Olympic minipost

 

Early on rope climbing, tug-of-war, and shooting live pigeons were Olympic events.  Over time there's been both churn and growth as audiences have changed and grown.   The International Olympic Committee recognizes a number of sports federations which government Olympic sports, potential Olympic sports and sports that would never be candidates (non-physical sports like chess and bridge and sports like auto racing and aerobatics that motors).   Getting a new sport into the Olympics involves politics and the television target market of the games.   The IOC has been worried about attracting a younger viewership so we have several Winter sports, BMX biking, skate boarding, sport climbing and surfing appear in recent years.  

 

Many of the new events are interesting from an amateur science point of view.  I was going to write about surfing, but there are a couple of key points that are better communicated visually.   This video does an excellent job covering the basics of why it is possible to surf including how you can travel faster than the wave.

 

 

the art of keeping a ball off your sand

A pre-Olympic post

 

Now a bit on one of my favorite sports - beach volleyball.   It's played on a sixteen by eight meter rectangular court on fine grained loosely compacted sand that's at least 40 cm deep.  The net is 2.43 meters high for me and 2.24 meters for women.  From there it's mostly similar to indoor volleyball.  Rather than going into rules it's more interesting to take a look into what's happening. (as with most sports there's much more going on than can be described in a few paragraphs, so just a few points - the videos give a better sense)

 

First a short segment featuring Canadians Sarah Pavan and Melissa Humana-Paredes. 

 

As the blocker, Sarah tends to stay near the net removing attack options from the other side.  Her height and jump gives her a larger set of options for placing the ball close to the net on the other side in very difficult to return locations.  Melissa's job is to cover the rest of the court - not exactly the easy task.  At 1.75m (5'9) Melissa is considered undersized, but makes up for it with amazing athleticism.  In the past decade both positions have become taller.  Five foot eleven female and six foot five male blockers are considered undersized.  Blockers, like basketball players, often have wingspans that are longer than their height.  Defenders are usually smaller as shorter limbs tend to accelerate faster.

 

Some women can serve the ball around 90 km/h (about 55 mph)  and men are about twenty percent faster.  The fastest serves deliver about 8,000 watts of power in the women's game and over eleven in the men's.   Putting things in perspective eight kilowatts is about eleven horsepower and a good reason for serious weight training.  Or consider that an electric cooking element on a range is about 1,800 watts.   But thanks to the fluid dynamics of the ball in flight and a need to test the other team the highest speeds aren't used all of the time.

 

Calculating the power of a jump is difficult - particularly in the sand - but the most athletic women probably generate an average power of 2,000 to 2,500 watts in their greatest efforts.   This is only for a few tenths of a second, but for reference Usain Bolt averaged about 2,600 watts for nearly a second at the beginning of his record race.  (These power levels are unsustainable - if you could average 500 watts for thirty minutes you could probably win the Tour de France.)  Near the net a player sometimes adjusts their center of gravity in a jump giving them hang times similar to that of a ballet dancer performing a grand jeté.  It's part of extending the window of being where you need to be and deception. 

 

You've probably noticed putting spin on a ball can add curve to its path.  It's called the Magnus effect and the size and low weight of the volleyball gives a more pronounced effect than most of the other sports (table tennis is the exception). Topspin is most commonly used and will drop the ball short of the expected flightpath - sometimes up to a meter with a lot of spin at an optimal speed.   And like baseball there's a narrow airspeed window with little or no spin on the ball where knuckleballs can occur.¹  The airspeed window for beach volleyball  is usually somewhere around 50 km/h  - a speed that is much more common in the women's game.   Like baseball it's difficult to master, but properly done the ball can unpredictably deviate from its normal path by as much as a ball  diameter by the time it makes it to the other side of the net making reception more difficult.

Sand wind sun and heat. 

The elements are part of the game.  Try running around in the sand,  particularly deep sand, changing directions and jumping.  Walking in the sand takes  at least one point six times as much energy as a solid surface. Running and jumping can take more - up to three times as much.  Agility is difficult without a lot of practice.  On the other hand diving into the sand is much safer than diving onto a harder surface.

 

Since the ball has only weighs about five eights as much as a soccer ball (football for most of the word), wind is an issue.   Players watch flags around the court to gauge the wind and will  drop sand to gauge it closer to the court. Windspeed and direction lead to "good" and "bad" sides of the court.  To even things out players switch sides at regular intervals.  As with other outdoor games heat, humidity, sunlight and shadows are issues. Moderate rain won't stop a game, but nearby lighting or heavy gusts associated with a storm will.

 

Games like baseball, volleyball, cricket and tennis share a feature based in our neurology.  Court size and ball speed are such that the fastest points average about four tenths of a second. Recognizing what's going on and reacting chews up a good deal of that time so players need to react without thinking.²   In beach volleyball deception is a common weapon.   Melissa "reads" the dynamic posture of her opponent and might notice a shift of weight to one leg.   She might change her own movement to make the other player think their intended move is correct.   Then, at the last moment, she'll make a small change and put the ball slightly out of reach on the other side of her opponent causing them to lose balance and miss the ball.   

 

You'll notice  most points see the receiving side touch the ball three times.  It can be done one or two, but usually the ball is carefully set and the two touches before the final touch allow time to read the other side and more accurately place the ball.  The best sets have incredible precision - usually within a few centimeters of where they need to be when the team is playing well.  

 

Sarah will tell you what separates the elite game is the mental component dealing with short term tactics and longer term strategies.  Communication between players and being able to "read" what the other side is doing - properly used it's probably the most powerful weapon they have.  Sarah and Melissa read simultaneously and have a sense of what the other sees.  They can communicate very rich contextual information to each other verbally and non-verbally. Each has to have a lot of trust in the ability and judgement of their teammate. Long term teams where each player knows each other physically, mentally and emotionally - who have the right "chemistry" in several dimensions - tend to dominate.

 

Here's another look at some long rallies where each team is reading well and reacting

 

 

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¹ There's a critical speed for a ball traveling through a fluid like the air at the boundary between turbulent and laminar flow.  Turbulent flow dominates at higher speeds, laminar at lower speeds.  Part of a spinning ball at this critical speed will be faster than the other so the drag on that part of the ball will be lower.   A zero spin an instability in airflow wanders oscillates around the edge of the ball somewhat unpredictably giving the swerving path of a knuckleball. 

² This is a very rich area in neurology.   Physical Intelligence by Scott Grafton is a great non-technical introduction to the neurology of movement.

 

 

a look at the movements of a goat

a pre-Olympic minipost

 

About a year ago I taught a course on the physics of sport. Recently a high frame rate video of Simone Biles was posted. Making a few frame by frame measurements (helped by another view and knowing her size and some simple home-brew software) it’s possible to do a quick back of the envelope analysis.

 

First the this slow motion video from a meet on the 4^th of June -watch it even if you’re not interested in the analysis. Her motions are beautiful.

 

Some background information .. she’s 142 cm tall - a shade under 4’8” and her weight is currently listed at 52 kg (about 114 pounds) Her top sprint speed is 8.0 m/s (18 mph), although she doesn’t reach it here (not enough room)

 

It’s important to note that a couple of innovations around 1980 revolutionized gymnastics. The floor is one of them .. notice how springy it is. It’s a thin carpet bonded to a layer of hard foam that’s glued to plywood sheets. All of this is mounted on a large array of heavy springs which are attached to the main floor. Think of it was a stiff trampoline that allows the gymnast to trade some of her kinetic energy into a higher jump. A pole vaulter uses the pole to do the same thing.

 

She launches at about 7 meters per second (about 15.7 mph) at an angle of about 70°. Her center of mass reaches a height of about 2.9 meters (9.5 feet) and she lands about 2 meters (6.5 feet) from her launch point. She lands on a piece of foam to slow the landing a bit. Even with that and the springy floor she’s experiencing a deceleration of over five times the force of gravity.

 

What goes on in flight is the remarkable part. Once launched, Simone is a projectile that is only acted on by the force of gravity (ok - there’s a small correction for wind resistance, but it can be ignored). She has three axes of rotation to play with. All three go through her center of mass, which is near her waist. Call the one that runs from head to toe her “twisting” axis. Call the second her tumbling axis ‘’ this one's at a right angle to her twist axis and is described by the motion about her waist when she falls forward. The third is at right angles to the other two and is the rotation to the left or right. She doesn’t use that one here, so we’ll ignore it.

 

Back to her sprint. She wants to go as fast as possible so she has the largest possible time in the air to accomplish her motions. Launch angle and speed together determine how high she’ll go and how much “hang time” she has. She also adds a bit of a twisting motion when she launches. She can speed it up by pulling her arms in like a skater. Likewise the tumbling motion can be speeded up by pulling her arms and legs in to lower the moment of inertia about that axis. The high speed of her flips - each is about two thirds of a second long and the smoothness of control is testament to her athleticism and precise control of her moments of inertia.

 

I did the calculation of a launch speed required to get another flip - another two thirds of a second - in… it would have to be about 10 meters per second (22.4 mph). Even with a very long runway we’re not going to see four full flips. A faster sprinter (world record for the 100m women’s sprint peaks around 12 meters per second) wouldn’t have the space and would be too tall and would lack the core body strength to do flips that fast anyway. We’re probably at the limit given the floor design and size along with human capabilities. Of course there are other innovations that can appear in future performances.

 

This is a great example of a sport that dictates body size and type - at least for the elite level.  That's an interesting subject on its own...