#Hothchester strikes back: the “terrorist” windshield threat on Rochester’s highways

We’ve been getting bombarded by reports over the last few months, at an ever-increasing rate: another reported incident of suddenly cracking windshields on 390, then 490 then even as far out as 104 in Ontario. Is there some lunatic waiting in the bushes, some wondered, waiting for their moment to do malevolence upon an unsuspecting car? Maybe someone with a near-silent air gun that might elude detection?

To test this particular hypothesis – that a pellet or BB gun might be able to shatter tempered glass – I started looking into the ultimate test case. That turns out to be a British-made pellet gun called the Daystate Air Ranger, a .22 calibre pellet rifle capable of firing at 1020 feet per second. Using the heaviest and therefore most destructive pellet I could find in that calibre, 32 grain, and an online impact force calculator, I came up with the following:

(2mv)/t or (2*0.00208kg*310mps)/1sec = ~1.29N

The tensile strength required by Federal Specification DD-G-1403B, which governs the definition of tempered glass, is 120 to 200N per square millimeter. In other words, while crazier things have happened, it is extremely unlikely that even the most powerful pellet gun will crack a windshield. And weighing in at $2000 for a single gun, it’s safe to say Daysiders are probably not that common in Rochester. Your kid’s Daisy plinker is woefully inadequate to the task, and not likely to be a suspect in this case, at all.

So, when all else fails, the best thing to do is look for the most obvious answer. And that answer is: weather.

Our winter was epic, as we all well know. Those of you who are on Twitter (and why aren’t the rest of you?) will be familiar with the great fun we all had with the #Hothchester hashtag:

Temperatures never seemed to go above zero for a month. Then, after an extraordinarily long, cold early spring, we suddenly shot up into the 80’s and 90’s, with barely a moment’s transition. This kind of weather plays havoc with all kinds of materials, but your car has probably borne the brunt of the abuse, spending all of it’s time out doors in the deep freeze.

And the thing is: tempered glass is very strong, but only because it is inherently unstable. The tempering process involves laying thin layer after thin layer of glass in an ever-thickening mat, in such a way that the tension lines in each layer oppose one another at odd angles. The result is that, since one layer wants to split in a direction directly opposite of another, the faults cancel each other out. In the event that something large enough hits the glass and shatters it, those tension lines will cause the glass to shatter into small, smooth-edged pellets that will only cause minor skin lacerations at best.

However, those tension lines get stressed by the shrinking that happens in extreme cold. Follow that up with the beating sun of an unexpectedly intense summer, and you’ve got a recipe for a whole lot of shattered windshields. Any small stone or nut from an overhanging tree could be enough to cause a crack. In fact, the window may spontaneously crack all on its own, as has been frequently reported in the past. Rest assured that when the crack happens, however it happens, it will be loud

Considering the fact that no one has observed a man by the side of the road; a bullet-shaped hole in a windshield; anything more major than a small crack in the windshield. Considering the fact that we can safely rule out pellet guns as a non-lethal, whisper-quiet means to shatter glass. Considering the fact that cracked windshields rarely make headlines in any other circumstance; that a whole industry is built around repairing minor cracks (Safelite, anyone?). Considering all these facts, it really begins to look like a jumpy police force and an overeager media community are making a very obvious problem into a self-propelled mystery.


Penn Yan flooding: conservation of mass and the physics of the flood.

Yesterday morning, New York woke up to find devastation in it’s Finger Lakes Region and Yates County. A shocking amount of rainfall has left high water marks as high as an estimated nine feet in some areas. A state of emergency has been declared and one would think that a Disaster Zone designation cannot be far behind. Events such as these seem comparatively routine in the South or along the Mississippi river delta. But even if flooding has become an increasingly common event in New York, devastation such as this feels like a new thing for our state.

Taking a step back from the human toll is helpful to understand the material damage with a bit of basic physics. Why is flood water so damaging?

At it’s most basic level, the real destructive power of water tends to come from a physical concept called the Conservation of Mass. This theory holds that, if a consistent mass of fluid is forced through a smaller channel, the water will either need to increase it’s velocity or else spread it’s mass out elsewhere to compensate. Regardless, the volume of water in movement (flux) on one side of the obstruction will be consistent with the volume of water in flux other side.

If this sounds technical and complicated, consider that everybody who waters their lawn or garden by holding their finger over the end of the garden hose is quite well aware of this effect. Instead of placidly arcing out of the hose to fall a foot in front of you, the constricted water column now sprays six or eight feet in front of you. But, if a flow of water was to go from a relatively wide channel to a narrower channel that’s still open at the top, the result would be the water running higher in the obstruction than out of it.

This silly video actually shows both effects more or less at once with a broken rubber pool. Note that, when the break happens, the water shoots out of the hole a good ten feet. But then when the pool edge falls below the water line, the water actually increases it’s height slightly to make it through the narrow channel at the top:

It also illustrates another, related characteristic of water: it’s preference for the path of least resistance. “Least resistence” does not necessarily mean “no resistance.”

In Penn Yan, we see these forces at work in pictures tweeted by Adam Chodak at 13WHAM ( @adamchodak ) of a gully that overtook the road it was supposed to protect (click for larger, clearer views):

Water’s true destructive force doesn’t just become visible when it reaches obstructions. It is created when it reaches that obstruction, as it rushes over, under, around and eventually, through the obstruction, leaving nothing in it’s wake. When you see swells in Penn Yan at 9 feet, some of those places may have been low elevation, but just as likely, they’re parts of downtown Penn Yan where the rushing water found it easier to increase it’s depth and velocity than to clear the obstruction in it’s way – which may very well have been a building.

In (simple, I promise) mathematical terms, the volume (Q) of water in “flux” – that is: moving – is equal to the height and width of the channel it’s moving through (collectively, A), times the velocity (v) at which it’s moving:

Q = vA

So if a body of water is moving 100 gallons of water a minute through a 5′ wide channel at 2′ high, the water is moving at 10 feet per minute(100 = 10(2*5) ). Constrict that channel to just two feet wide, and the water will either need to rise to 5′ high, or else increase it’s velocity to 25 feet per minute.

Every other destructive power of flood water extends from this one basic physics concept. Just two feet of relatively placid water can lift a vehicle 3000 pounds or more. As we can see, higher water and higher velocity can do a lot more damage.


Tasty T-Day Science: why does vinegar keep poached eggs together?

Yum. Poached eggs. The stuff of foodie dreams, with the runny yolk that makes a sauce for whatever lies beneath it. And for those of you who get your Thanksgiving on early in the day (and there are lots of you, don’t lie), your day of thanks may very well begin with one of these delicacies on toast. Or a Toad in the Hole, for you Brits.

If you’ve noticed, most people who make poached eggs with some regularly tend to use a few drops of vinegar in the water. Why is this? The answer has nothing whatsoever to do with flavour. It has to do with physics and specifically, with a concept known as molecular polarity.

But let’s back up a step. Poaching is about cooking food in hot water. Boiling, essentially. The thing with an egg is: you face the obvious problem of trying to poach something which is itself liquid. Dropping the egg into a pot of boiling water should, we would expect, cause the egg to spread out evenly in the pot. But that is not what we want when we poach an egg. We want a nice, fluffy cloud of egg that can be taken out whole and dropped onto whatever foods we wish to bathe in unctuous goodness. This requires that the white or albumen of the egg poach quickly and more or less in one place.

Water’s molecular structure. Note the polarity of the two elements. Photo:

The trick, though, is that water has a chemical structure that is built to be magnetic. With its negatively-charged oxygen ion on one side and its positively-charged hydrogen ion on the other, water forms a natural magnet. That magnetism is called molecular polarity, and allows it to do two things: create a meniscus at the top of a column of water and more importantly for our discussion, naturally adhere to other surfaces.

An example of water’s molecular polarity in action. Note the beads of water formed by surface tension.
Notice. Them.
Photo: Blue Waikiki

That ability to adhere to other surfaces is the problem, because it’s what draws the egg out of its nice shape and into nastiness. But vinegar, while it still has some molecular polarity, is nowhere near as magnetic. By introducing a few drops of vinegar into the water, you can change the overall ability of the cooking liquid to leech albumen out of shape.

So, yet another reason that vinegar is a must-have for any kitchen, even if you don’t particularly like the taste. What else is vinegar good for? Well, it is a natural counterbalance to heat. If you’ve made that chili a wee bit too hot for the little ‘uns, add a couple of dashes of vinegar to the pot. You’ll never taste the acid of the vinegar, but the heat will be magically cut. Hmm… Maybe I just came up with another Tasty T-Day Science article…

And Spotify users, don’t forget to check out Jillian and I on Spotify, where we’ve created a Turkey Day set list of truly awful “turkeys.” Great, cheesy fun!


The science behind the cutest cat video you’ll see all day

Yes, this is in fact the cutest video you’re likely to see all day. This unfortunate feline wants to drink out of the kitchen sink faucet, but clearly, has developed a somewhat unorthodox method of doing so. Basically, dunk your head and lick the water off your chops:

But funny as this video is by itself, we here at DFE would be remiss if we simply posted a link to the video without an explanation. Yes, as you probably already guessed, there is in fact a reason for this cat’s strange behavior. And it has to do with the way that cats drink water normally.

We see a cat licking at a water bowl and most of us think we know what’s happening: the cat is dipping its tongue into the water and grabbing a little drop’s worth into its mouth. But that is in fact not at all what is happening. What is actually happening is a bit of tricky physics.

The cat in fact flicks its tongue in and out of the water to create a column of water that extends from the bowl to its mouth. This is in part because, unlike humans, cats mouths cannot produce suction. Instead, creating this column of water moving towards their mouths pits the inertia of the water heading towards them against gravity, which is pulling the water back down. As long as the cat is able to move their tongue faster than the gravitational pull wants to pull the water down, they’re able to drink. Thus cats achieve the same basic results as we do when using a straw, but without any surrounding vessel to provide lift.

So now, you can start your weekend.