How to Make a Sled Go Faster, According to Science

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iStock

So you have a need for speed. Sled speed. You've already picked a steep slope and streamlined your form. Maybe you're wearing a skintight Lycra luge racing suit and have shaved your head. Maybe you've shaved everything—when you're battling air resistance, you can't leave anything to chance.

Let's assume you've scratched all that off your to-do list and now want to reduce friction between your sled and the ground. In other words, you're Clark Griswolding this sucker and need some solid toboggan lube.

Can science help you go faster? Yes, it can.

The science of friction and lubrication—what's called tribology—has focused greatly on snow and ice: The research is valued by avalanche researchers, automobile and tire manufacturers, and America's $20 billion winter sports industry. The consensus? You need to exploit the properties of "melt-water lubrication."

When sledders zoom down a hill, they're not traveling atop pure snow—they're skimming across a microscopically thin layer of meltwater. This water, created by the friction of the moving sled, is your primary lubricant. According to researchers [PDF] at the ski company Swix, the ideal meltwater layer is 50 molecules thick and occurs at around 32°F. Anything warmer will produce excess meltwater that can cling to your sled. This process, called capillary drag, decreases speeds.

Bitterly cold snow isn't better. When the mercury drops below 14°F, it's difficult to find a significant layer of lubricating meltwater. "When it's that cold, the liquid layer is not going to form without an excessive amount of friction," Kenneth Libbrecht, a Caltech physicist and snowflake specialist (who also served as snowflake consultant on Disney's Frozen), tells Mental Floss. In these conditions, the meltwater layer may be as thin as a single H20 molecule, making your sled scrape against the asperities, or rough edges, of packed snow. You might as well be attempting to ride down a sand dune [PDF].

Unless you're the Winter Warlock or the Chinese government, you probably can't control the weather—but you can control how you prepare for it. Research shows that when it's wet and warm, a rough-bottomed sled etched with a shallow front-to-back pattern may be helpful. The pattern provides a smaller surface area for water molecules to grab, decreasing capillary drag.

At colder temperatures, when snowflakes are sharper and harder, it's important to make the bottom of your sled harder so you can plow over any asperities that would otherwise "grab" at your toboggan and slow you down. So coat the bottom of your sled in a hard, smooth substance like a synthetic hydrocarbon ski wax.

But no matter the temperature, the best way to skim over the meltwater layer is to lube up the bottom of your sled with hydrophobic materials, substances such as grease, oil, and wax that are literally "afraid of water." After consulting with the experts, I tested several hydrophobic lubricants—and I found them all in my house.

ONE MAN, ONE SLED, AND SIX LUBRICANTS

Our experiment took place at the public sledding hill in Woodstock, New York, wedged below the foothills of the Catskill Mountains. The thermometer read 29°F—firmly in the not-too-hot, not-too-cold meltwater Goldilocks Zone—and my backpack was stuffed with everyday hydrophobic materials: a $0.98 wax candle from Walmart, WD-40, PAM cooking spray, a hardwood paste wax, Adobo All-Purpose Seasoning, and bacon grease.

My vehicle? An $11 plastic blue-green sled that was clearly intended to ferry small children.

The slope here was gentle, but the snow was not. It was old, crusty, and hard. I later asked Libbrecht—who has classified 35 different types of snowflakes ("most of them look like sand, just little globs")—how conducive such a surface is for good speed-sledding. He explained that the shape of snowflakes changes quickly upon hitting the ground, becoming more spherical and smooth as they're compacted by the wind, sun, and other sledders. In other words: Like people, snow gets rounder with age.

This is great news for speed, but not so great for steering. On my first dry test run—my control—my average speed was approximately 12.6 mph. On my way down, I completed three pirouettes and cried for help at least once.

Wax Candle

unlit candle in metal holder
iStock

My 12.6-mph pace was a far cry from the world record for fastest sled run (83.5 mph), so I turned to wax.

Downhill snow racers have been using wax for more than a century. Before the 1940s, people tried a wide variety of natural substances to make the sled bottom slick, including beeswax, whale oil, pine resin, and tallow. By the mid-century, tobogganers rubbed their sleds with wax paper or a handy candle. Candles contain paraffin wax, a mix of straight-chained saturated hydrocarbons that contain 20 to 40 carbon atoms.

According to the book The Physics of Skiing, by David Lind and Scott P. Sanders, straight-chained hydrocarbons are the way to go. These molecules orient themselves in parallel structures and have strong intermolecular bonds, which keeps the wax hard at cool temperatures—thus giving better gliding properties. The molecules are also non-polar and don't interact kindly with polar molecules such as water. (Chunkier hydrocarbons, however, that have short chains branching off the primary chain, are softer and "more suitable for … waxes designed to increase traction or grab," write Lind and Sanders.)

Paraffin wax is also relatively hard and should do a good job riding over snow asperities as long as the snow isn't bitterly cold. And it does: For two minutes, I rubbed the cold candle into the base of the sled using a circular motion. Once my butt hit the sled, I was cruising. I hit approximately 17.98 mph.

WD-40

According to a comprehensive list, WD-40 has more than 2000 uses: It can remove gum from school bus seats, lubricate the wheels of tuba cases, and even prevent puppies from chewing on telephone lines. Also on the list: "Lubricates sleds and toboggans" [PDF].

This is no surprise: WD stands for "water displacement." And while the formula is technically secret, the sleuths at WIRED used gas chromatography in 2009 to reveal the black magic inside. Their conclusion: alkanes. Alkanes are water-repellant hydrocarbons that refuse to bond with either hydrogen or oxygen. In other words, exactly what I need under my sled.

It worked: After a noxious 10-second spray, the WD-40 clocked the same time as candle wax. But, phew, did my trip smell ungodly. Not only that, but I later learned that some alkanes are key to the German cockroach's ability to produce pheromones meant to attract mates. So I had that to look forward to.

PAM Original No-Stick Cooking Spray

If I were a scientist, I'd be testing all of these materials with the aim of determining their coefficient of friction, a figure that quantifies the amount of friction between two surfaces. It can be expressed by the following formula, which is, fittingly, dying to spell the word fun.

mathematical formula for sledding down a hill
Lucy Quintanilla, Mental Floss

You can measure the kinetic friction of materials with an instrument called an oscillograph. Unfortunately, I work for a media company. We don't have oscillographs.

However, I wish I had one for this part of the experiment. Because while the coefficient of friction for this skin-scraping snow was certainly low, I can't speak for my sled rub-a-dub-dubbed in canola oil. It should have had a low coefficient of friction, but the "No-stick" spray lived true to its name in all the wrong ways—by failing to stick to the bottom of my sled. It disappeared almost immediately, making my PAM time just as slow as my control run.

Hardwood Paste Wax

Paste wax is the lubricant of champions. Just ask Tom Cox, a former champion of the U.S. National Toboggan Championships, held annually in Camden, Maine. Cox is also its chief toboggan inspector, ensuring that the 400 wooden sleds that race every year meet the competition's guidelines.

He's seen all sorts of substances slathered onto the bottom of sleds, from cross country wax to lemon Pledge. "Everybody does it different, and I can't tell you what the secret is," Cox tells Mental Floss. "I won the whole thing in 2003, and we used a paste wax, a hardwood floor wax, but I don't know if that's the answer, because I haven't won since."

Cox may be stuck in a competitive rut, but he's a proven champion, and I trust his methods. That said, I quickly learned that paste wax is best smeared on wood, not plastic. Using my hands, I spread the soft wax; it was lumpy and uneven, like dried-out peanut butter. I attracted quizzical glances from passersby who perhaps thought I was gobbing sandwich spread onto my sled. Oh, and it left a chunky brown trail of goop down the hill.

But who cares? My sled nearly hit 20 miles per hour.

In conditions like these, flirting with snow's melting point, a softer wax like paste wax may be ideal. The coefficient for waxed wood on dry snow is remarkably low: 0.04. (The closer the number is to zero, the slippier it is. For comparison, the coefficient for ice-against-ice is around 0.03.) I can only imagine how low the number might be for a plastic kiddie sled.

Adobo All-Purpose Seasoning

Another special ingredient that has also appeared on the bottom of sleds at the National Toboggan Championships? Onion powder.

Some sledders think that applying a fine powder is like adding tiny ball bearings to the bottom of a sled. In truth, a mildly grainy bottom may help reduce capillary drag in warm conditions, stopping any clingy meltwater from hitching a ride. You can see this happen with superhydrophobic materials such as lotus leaves, which are composed of thousands of tiny microscopic pillars. Those raised bumps decrease the points of contact between the leaf and a water droplet, ensuring that water will simply roll off. In fact, dozens of ski wax manufacturers are attempting to create waxes that mimic the nanostructure of lotus leaves. It's this principle that I hoped I could achieve with onion powder.

But when I couldn't find onion powder in my kitchen, I turned to Adobo seasoning, which might as well be the WD-40 of seasoning. Chicken. Steak. Chicken-fried steak. You can sprinkle this pixie dust on anything and it just works. Adobo might not contain onion powder, but if it can trick unwitting people into believing that I'm a talented cook, perhaps it could work similar magic on my sledding abilities. I wetted the bottom of my sled with a spritz of water and generously seasoned my plastic chariot.

It flopped. Whatever the reason, after three futile attempts down the hill, all the Adobo did was leave behind a glowing trail of yellow snow.

Bacon Grease

bacon frying in a pan
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Before the 2018 Super Bowl, Philadelphia police prevented rabid Eagles fans from converting local streetlights into adult-sized monkey bars by scrubbing the city's utility poles with Bio-Bottle Jack Hydraulic Fluid, an environmentally friendly lubricant. I was hungry to apply this legendary goo to my sled, but when I called local suppliers and asked to purchase it, all of them told me delivery would take weeks. I suspected the city of Philadelphia had gobbled up the east coast's stockpile.

So I turned to the NFC Championship Game, when Philly's police slathered utility poles with Crisco. Thankfully, I had a better alternative in my fridge: bacon fat. Anybody who has tried to wash their hands of rendered pig blubber knows that it hates water. Indeed, the grease spread onto my sled like melted butter. It was soft and waxy, and its smell mingled with all of the other scents on my hands—vanilla, canola oil, aerosol propellant, potential cockroach pheromone, paste wax, chicken seasoning—to create a miasma that is beyond my abilities to describe. I may or may not have licked my fingers. I may or may not have regretted it.

Around this time, a mother and a small child began walking toward the hill. I waved to them. They stopped and gaped at me, this disheveled grown man sitting alone on a hill of brown and yellow snow, surrounded by discarded bottles of WD-40 and all-purpose seasoning, vigorously scrubbing a strange grease on the bottom of a fluorescent sled built for small children. The mother grabbed her child's hand and scurried in the opposite direction.

Anyway! Bacon grease clocked in at 17 miles per hour.

Perhaps I applied the grease too thickly. According to Lind and Sanders, an application of running wax should be between 0.005 and 0.02 millimeters thick: "If these final wax layers were any thicker, they would be more likely to pick up dirt from the surface of the snow, which, as we have seen, would increase friction."

In other words, there is such a thing as too much lube. When I buffed down the bacon grease with a cloth towel, I hit 19 miles per hour.

TIPS FOR YOUR RIDE

My sledding experiments weren't exactly scientifically rigorous. They weren't properly controlled. My sled never took the same route down the hill. The number of confounding variables that could have skewed each result is, well, confounding.

But the results do echo the advice of experts: If you can, sled in temperatures around 32°F, when the meltwater is an optimal thickness. Avoid the temptation of freshly fallen snow, and wait for those sharp snowflakes to be smoothed into a polished sledding path. If you have a wooden sled, sand it. (According to Cox, "The ones that go the fastest [at the National Toboggan Championships] are sanded before you put wax on it, sanded with a very, very fine paper, maybe 1500 grit.") If you can, choose an inner tube over a plastic sled. In a 2009 Journal of Trauma study titled "Sledding: How Fast Can They Go?" researchers found that inner tubes travel an average of 2 mph faster than plastic.

If you must use plastic, opt for polyethylene. It's hydrophobic and cheap. According to the glaciologist Samuel Colbeck, polyethylene is "hard, highly elastic, can be smoothed and imprinted with different patterns, can be made porous, can be easily coated with waxes, does not readily adhere to ice, and has a [coefficient of friction] that is not greatly affected by surface contamination" [PDF]. Lastly, coat your sled in a hydrophobic wax: A fluorocarbon ski wax is optimal, but do-it-yourselfers can always keep a candle in their pocket.

Also, bring Adobo. It won't make your sled faster, but it will leave a trail of bright yellow snow, guaranteeing you will have the hill all to yourself.

 

For more on the physics of snow sports, Mental Floss recommends David Lind and Scott P. Sanders's remarkable and authoritative book The Physics of Skiing.

12 Facts About the Sense of Taste

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iStock/m-imagephotography

A lot more than your tongue is involved in the process of tasting food. Taste is not only one of the most pleasurable of the five senses, but a surprisingly complex sense that science is beginning to understand—and manipulate. Here are 12 fascinating facts about your ability to taste.

1. Everyone has a different number of taste buds.

We all have several thousand taste buds in our mouths, but the number varies from person to person. The average range is between 2000 and 10,000. And taste buds are not limited to your tongue; They can be found in the roof and walls of your mouth, throat, and esophagus. As you age, your taste buds become less sensitive, which experts believe may be why foods that you don’t like as a child become palatable to you as an adult.

2. You taste with your brain.

The moment you bite into a slice of pie, your mouth seems full of flavor. But most of that taste sensation is happening in your brain. More accurately, cranial nerves and taste bud receptors in your mouth send molecules of your food to olfactory nerve endings in the roof of your nose. The molecules bind to these nerve endings, which then signal the olfactory bulb to send smell messages directly to two important cranial nerves, the facial nerve and the glossopharyngeal nerve, which communicate with a part of the brain known as the gustatory cortex.

As taste and nerve messages move further through the brain, they join up with smell messages to give the sensation of flavor, which feels as if it comes from the mouth.

3. You can’t taste well if you can’t smell.

When you smell something through your nostrils, the brain registers these sensations as coming from the nose, while smells perceived through the back of the throat activate parts of the brain associated with signals from the mouth. Since much of taste is odor traveling to olfactory receptors in your brain, it makes sense that you won’t taste much at all if you can’t smell. If you are unable to smell for reasons that include head colds, smoking cigarettes, side effects of medications, or a broken nose, olfactory receptors may either be too damaged, blocked, or inflamed to send their signals on up to your brain.

4. Eating sweet foods helps form a memory of a meal.

Eating sweet foods causes your brain to remember the meal, according to a 2015 study in the journal Hippocampus, and researchers believe it can actually help you control eating behavior. Neurons in the dorsal hippocampus, the part of the brain central to episodic memory, are activated when you eat sweets. Episodic memory is that kind that helps you recall what you experienced at a particular time and place. "We think that episodic memory can be used to control eating behavior," said study co-author Marise Parent, of the Neuroscience Institute at Georgia State. "We make decisions like 'I probably won't eat now. I had a big breakfast.' We make decisions based on our memory of what and when we ate."

5. Scientists can turn tastes on and off by manipulating brain cells.

Dedicated taste receptors in the brain have been found for each of the five basic tastes: sweet, sour, salty, bitter, and umami (savory). In 2015, scientists outlined in the journal Nature how they were able to turn specific tastes on or off in mice, without introducing food, by stimulating and silencing neurons in the brains. For instance, when they stimulated neurons associated with “bitter,” mice made puckering expressions, and could still taste sweet, and vice versa.

6. You can tweak your taste buds.

Most of us have had the experience of drinking perfectly good orange juice after brushing our teeth, only to have it taste more like unsweetened lemon juice. Taste buds, it turns out, are sensitive enough that certain compounds in foods and medicines can alter our ability to perceive one of the five common tastes. The foaming agent sodium lauryl/laureth sulfate in most toothpaste seems to temporarily suppress sweetness receptors. This isn't so unusual. A compound called cynarin in artichokes temporarily blocks your sweet receptors. Then, when you drink water, the cynarin is washed away, making your sweet receptors “wake up” so the water tastes sweet. A compound called miraculin, found in the herb Gymnema sylvestre, toys with your sweet receptors in a similar way.

7. The smell of ham can make your food “taste” saltier.

There’s an entire industry that concocts the tastes of the food you buy at the grocery store. Working with phenomena known as phantom aromas or aroma-taste interactions, scientists found that people associate “ham” with salt. So simply adding a subtle ham-like scent or flavor to a food can make your brain perceive it as saltier than it actually is. The same concept applies to the scent of vanilla, which people perceive as sweet.

8. Your taste buds prefer savory when you fly.

A study by Cornell University food scientists found that loud, noisy environments, such as when you’re traveling on an airplane, compromise your sense of taste. The study found that people traveling on airplanes had suppressed sweet receptors and enhanced umami receptors. The German airline Lufthansa confirmed that on flights, passengers ordered nearly as much tomato juice as beer. The study opens the door to new questions about how taste is influenced by more than our own internal circuitry, including our interactions with our environments.

9. Picky eaters may be “supertasters.”

If you’re a picky eater, you may have a new excuse for your extreme dislike of eggplant or sensitivity to the slightest hint of onion. You might be a supertaster—one of 25 percent of people who have extra papillae in your tongue. That means you have a greater number of taste buds, and thus more specific taste receptors.

10. Some of your taste preferences are genetic.

While genetics may not fully explain your love of the KFC Double Down or lobster ice cream, there may be code written into your DNA that accounts for your preference for sweet foods or your aversion to certain flavors. The first discovery of a genetic underpinning to taste came in 1931, when chemist Arthur Fox was working with powdered PTC (phenylthiocarbamide), and some of the compound blew into the air. One colleague found it to have a bitter taste, while Fox did not perceive that. They conducted an experiment among friends and family and found wide variation in how (and whether) people perceived the flavor of the PTC to be bitter or tasteless. Geneticists later discovered that the perception of PTC flavor (similar to naturally occurring compounds) is based in a single gene, TAS2R38, that codes for a taste receptor on the tongue. In a 2005 study, researchers at the Monell Chemical Senses Center found that the version of this gene also predicted a child's preference for sweet foods.

11. Your genes influence whether you think cilantro tastes like soap.

There may be no flavor more hotly debated or deeply loathed than the herb cilantro (also known as coriander). Entire websites, like IHateCilantro.com, complain about its “soapy” or “perfumy” flavor, while those who like it simply think it gives a nice kick to their salsa. Researchers at the consumer genetics company 23andMe identified two common genetic variants linked to people's “soap” perceptions. A follow-up study in a separate subset of customers confirmed the associations. The most compelling variant can be found within a cluster of olfactory receptor genes, which influence our sense of smell. One of those genes, OR6A2, encodes a receptor that is highly sensitive to aldehyde chemicals, which cilantro contains.

12. Sugar cravings have a biological basis.

Your urge for more hot fudge may have little to do with a lack of self-control. Scientists think that our yearning for sweets is a biological preference that may have been designed to ensure our survival. The liking for sweet tastes in our ancient evolution may have ensured the acceptance of sweet-tasting foods, such as breast milk and vitamin-rich fruits. Moreover, recent research suggests that we crave sweets for their pain-reducing properties.

Yes, You Have Too Many Tabs Open on Your Computer—and Your Brain is Probably to Blame

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iStock.com/baona

If you’re anything like me, you likely have dozens of tabs open at this very moment. Whether it’s news stories you mean to read later, podcast episodes you want to listen to when you have a chance, or just various email and social media accounts, your browser is probably cluttered with numerous, often unnecessary tabs—and your computer is working slower as a result. So, why do we leave so many tabs open? Metro recently provided some answers to this question, which we spotted via Travel + Leisure.

The key phrase to know, according to the Metro's Ellen Scott, is “task switching,” which is what our brains are really doing when we think we're multitasking. Research has found that humans can't really efficiently multitask at all—instead, our brains hop rapidly from one task to another, losing concentration every time we shift our attention. Opening a million tabs, it turns out, is often just a digital form of task switching.

It isn't just about feeling like we're getting things done. Keeping various tabs open also works as a protection against boredom, according to Metro. Having dozens of tabs open allows us to pretend we’re always doing something, or at least that we always have something available to do.

A screenshot of many tabs in a browser screen
This is too many tabs.
Screenshot, Shaunacy Ferro

It may also be driven by a fear of missing information—a kind of “Internet FOMO,” as Travel + Leisure explains it. We fear that we might miss an important update if we close out of our social media feed or email account or that news article, so we just never close anything.

But this can lead to information overload. Even when you think you're only focused on whatever you're doing in a single window, seeing all those open tabs in the corner of your eye takes up mental energy, distracting you from the task at hand. Based on studies of multitasking, this tendency to keep an overwhelming number of tabs open may actually be altering your brain. Some studies have found that "heavy media multitaskers"—like tab power users—may perform worse on various cognitive tests than people who don't try to consume media at such a frenzied pace.

More simply, it just might not be worth the bandwidth. Just like your brain, your browser and your computer can only handle so much information at a time. To optimize your browser's performance, Lifehacker suggests keeping only nine tabs open—at most—at one time. With nine or fewer tabs, you're able to see everything that's open at a glance, and you can use keyboard shortcuts to navigate between them. (On a Mac, you can press Command + No. 1 through No. 9 to switch between tabs; on a PC, it's Control + the number.)

Nine open tabs on a desktop browser
With nine or fewer tabs open, you can actually tell what each page is.
Screenshot, Shaunacy Ferro

That said, there are, obviously, situations in which one might need many tabs open at one time. Daria Kuss, a senior lecturer specializing in cyberpsychology at Nottingham Trent University, tells Metro that “there are two opposing reasons we keep loads of tabs open: to be efficient and ‘create a multi-source and multi-topic context for the task at hand.’” Right now, for example, I have six tabs open to refer to for the purposes of writing this story. Sometimes, there's just no avoiding tabs.

In the end, it's all about accepting our (and our computers') limitations. When in doubt, there’s no shame in shutting down those windows. If you really want to get back to them, they're all saved in your browser history. If you're a relentless tab-opener, there are also browser extensions like OneTab, which collapses all of your open tabs into a single window of links for you to return to later.

[h/t Travel + Leisure]

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