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How a Differential Gear Works

Ever wondered how a differential gear on a car works? Well, if you're like me, your first question is just what the heck is a differential? Wikipedia says (emphasis added):

A vehicle's wheels rotate at different speeds, mainly when turning corners. The differential is designed to drive a pair of wheels with equal force, whilst allowing them to rotate at different speeds. In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive mechanism. When cornering, the inner wheel needs to travel a shorter distance than the outer wheel, so with no differential, the result is the inner wheel spinning and/or the outer wheel dragging, and this results in difficult and unpredictable handling, damage to tires and roads, and strain on (or possible failure of) the entire drivetrain.

This video explains the whole thing (note: the first two minutes or so are a demonstration of synchronized motorcycle riding, which you may or may not find exciting). It's kitschy, but also educational -- through a step-by-step engineering demonstration, this vintage video makes it clear how all this technical car stuff works. Chevrolet Motor Division (General Motors Sales Corporation) Presents: AROUND THE CORNER...

See also: Richard Feynman Explains Trains, in which he explains a similar issue faced by trains turning corners on train tracks.

(Via Kottke.org.)

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A Step-by-Step Journey Through Your Body's Digestive System
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We at Mental Floss write a lot about poop, but not as often about how our bodies produce the stuff in the first place. Humans eat between two and six pounds of food per day—and as TED-Ed’s latest video explains, this grub passes through an elaborate network of channels, organs, tissues, and nerves that’s commonly known as the human digestive system.

The digestive system is the unsung hero of our torso. Its 10 organs—which include the esophagus, liver, intestines, and stomach—contain over 20 specialized cell types, and the gastrointestinal track alone has an internal surface area of between 320 and 430 square feet. But the digestive process doesn’t begin and end with the esophagus—it starts in our mouths.

The body produces just over six cups of saliva per day, a process that begins when we start salivating over a tasty morsel. This clear substance contains starch-busting enzymes, which break the food we eat into a moist lump (a bolus) that will eventually become the stuff that comes out our other ends. In all, this journey lasts between 30 and 40 hours—and you can follow it step by step by watching TED-Ed’s video below.

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Today's Wine Glasses Are Almost Seven Times Larger Than They Were in 1700
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Holiday party season (a.k.a. hangover season) is in full swing. While you likely have no one to blame but yourself for drinking that second (or third) pour at the office soiree, your glassware isn't doing you any favors—especially if you live in the UK. Vino vessels in England are nearly seven times larger today than they were in 1700, according to a new study spotted by Live Science. These findings were recently published in the English medical journal The BMJ.

Researchers at the University of Cambridge measured more than 400 wineglasses from the past three centuries to gauge whether glass size affects how much we drink. They dug deep into the history of parties past, perusing both the collections of the Ashmolean Museum of Art and Archaeology at the University of Oxford and the Royal Household's assemblage of glassware (a new set is commissioned for each monarch). They also scoured a vintage catalog, a modern department store, and eBay for examples.

After measuring these cups, researchers concluded that the average wineglass in 1700 held just 2.2 fluid ounces. For comparison's sake, that's the size of a double shot at a bar. Glasses today hold an average of 15.2 fluid ounces, even though a standard single serving size of wine is just 5 ounces.

BMJ infographic detailing increases in wine glass size from 1700 to 2017
BMJ Publishing group Ltd.

Advances in technology and manufacturing are partly to blame for this increase, as is the wine industry. Marketing campaigns promoted the beverage as it increasingly became more affordable and available for purchase, which in turn prompted aficionados to opt for larger pours. Perhaps not surprisingly, this bigger-is-better mindset was also compounded by American drinking habits: Extra-large wineglasses became popular in the U.S. in the 1990s, prompting overseas manufacturers to follow suit.

Wine consumption in both England and America has risen dramatically since the 1960s [PDF]. Cambridge researchers noted that their study doesn't necessarily prove that the rise of super-sized glassware has led to this increase. But their findings do fit a larger trend: previous studies have found that larger plate size can increase food consumption. This might be because they skew our sense of perception, making us think we're consuming less than we actually are. And in the case of wine, in particular, oversized glasses could also heighten our sensory enjoyment, as they might release more of the drink's aroma.

“We cannot infer that the increase in glass size and the rise in wine consumption in England are causally linked,” the study's authors wrote. “Nor can we infer that reducing glass size would cut drinking. Our observation of increasing size does, however, draw attention to wine glass size as an area to investigate further in the context of population health.”

[h/t Live Science]

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