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Lycra, the Fabric of Spacetime

YouTube / apbiolghs
YouTube / apbiolghs

In this video, physics teacher Dan Burns explains gravity using a sheet of lycra as the "fabric of spacetime." It's a classic demo, and you can even build your own circular universe on the cheap! (Apparently spandex works well too.)

There's a brief joke in the video referring to the Coriolis Effect. For more on that, see Australian Toilets Don't Flush Backwards Because of the Coriolis Effect.

(Via Kottke.)

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Impossible Figure Skating Moves from the Movies
Paramount Home Video
Paramount Home Video

Figure skating is always one of the most anticipated events during the Winter Olympics. But in Hollywood, filmmakers have taken a few liberties on the ice, namely when it comes to some of the technical elements. And the judges are not impressed. Here are a couple of skating moves that could never have been completed without a bit of movie magic.

THE CUTTING EDGE

It's a climactic moment near the end of the 1992 movie, The Cutting Edge, when figure skater Kate Moseley (played by actress Moira Kelly) turns to her pairs partner Doug Dorsey (D.B. Sweeney) just before they are to take the ice at the Olympics and excitedly declares, “We're doing the Pamchenko!”

Frantic, Doug tries to talk her out of it. “Forget it. It's too dangerous,” he yells over the sound of the cheering crowd at the skating arena.

They argue right up to the very moment their music starts on the ice about whether to attempt the controversial “Pamchenko twist,” a highly difficult and dangerous maneuver their coach invented that, if completed during their skate, would mean an instant gold medal. Long story short (spoiler), they execute the move flawlessly and the movie ends with no doubt that they've won Olympic gold.

It's a triumphant ending. But let's just say there's a very good reason the filmmakers used a series of cuts to create the illusion that they actually did the move. The truth is, the Pamchenko twist is impossible.

Earlier in the film, coach Anton Pamchenko (Roy Dotrice) tosses a bunch of weathered looking diagrams onto the ice during a practice that detail a highly dangerous pairs move he has been inventing for the last 20 years.

Intrigued, Doug takes a look. “A bounce spin into a throw twist ... and I catch her?”

The Pamchenko twist does have a basis in reality. It is composed of two parts, as Doug deftly put it. The first part is a “bounce spin,” which is a real move that is actually illegal in competition, per International Skating Union rules. It's often performed in exhibitions and shows because it is quite a death-defying crowd-pleaser—the man grabs the woman by her feet and swings her up and down as he rotates. The woman's head typically comes mere inches from smashing on the ice if it is done correctly. If done incorrectly ... well, just try not to think about that.

The second part is a “throw twist,” more commonly known as a “split twist.” This is a required technical element in high-level pairs competition. To get full credit, a man and woman must start skating backward together. The male partner typically launches the female above his head, where she splits her legs and twists in midair as she pulls them back together. The man catches her as she comes down. Elite-level pairs teams regularly complete triple-twists (the woman does three rotations in the air). Two-time Olympic champions Ekaterina Gordeeva and Sergei Grinkov completed a textbook split triple-twist in their long program in the 1988 Olympics—the first technical element in this video.

Now, put the bounce spin together with the throw twist. The physics just don't compute. The centrifugal force built up during the bounce spin would launch the woman—assuming she is released at the highest point of the bounce spin—on a parabolic trajectory. In theory, she could use the momentum to twist in the air, but it's highly unlikely that she would be thrown high enough to pull it off without getting her head smashed onto the ice during the bounce spin. And even if she did, the horizontal trajectory would launch her so far away from her partner that there's no realistic way he could have enough time to stop his own momentum from the spinning and traverse the distance to catch her.

Pamchenko says in the film that it's all about the timing. But frankly, it's not worth risking the horrifying injuries that would inevitably result to test his theory. There are plenty of other legal and physically possible moves pairs skaters can spend their time and energy perfecting.

BLADES OF GLORY

In Blades of Glory, Will Ferrell and Jon Heder play two champion singles skaters who are banned from men's competition for life after an unseemly incident at a competition. Desperate to get back on the ice, they team up as a pair. In order to stand a chance of beating reigning pairs champions Stronz and Fairchild (Amy Poehler and Will Arnett), they attempt a highly dangerous and difficult maneuver called the Iron Lotus—which has only ever been attempted in North Korea with comically disastrous results.

If the Pamchenko twist is impossible, the Iron Lotus is downright laughable—which is the point, of course. It starts out the same way, with a bounce spin. However, at the height of the bounce, the male skater launches the female into a back flip instead of a twist. While she's flipping, he does an Arabian cartwheel underneath her. Once completed, he catches her by the arm and leg, and the pair gracefully rotate out of it together.

“I swear to God, if you cut my head off,” Chazz Michael Michaels (Ferrell) warns his partner, Jimmy MacElroy (Heder), before they attempt it in the final performance of the film. As they launch into it, their coach (Craig T. Nelson) screams, “No! Don't do it! I was wrong, it's suicide!”

But wordlessly, magically, they nail it. Or rather, computer-animated stunt doubles nail it, because it's physically impossible. It would require the “female” skater to reverse her momentum in mid-air to transition from the bounce spin into the back flip. Maybe it's possible on the moon, where gravity isn't so much of a factor.

So what have we learned from this little figure skating physics lesson? You won't be seeing any Pamchenko twists or Iron Lotuses in Pyeongchang. And don't try any of this at home.

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7 Science-Approved Tips for Walking Across Ice
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iStock

Unless you live in a warm climate year-round where the only ice you experience involves cubes that tumble from your refrigerator door, the issue of slipping on the slick surface presents a serious concern. After all, news segments talk of treacherous conditions where people unable to gain traction slide themselves into oblivion just crossing the street. On the work front, the Bureau of Labor Statistics reports that in 2014, ice, snow, or sleet caused more than 42,000 injuries and illnesses.

And of course, there will always be viral ice-slipping videos floating around, like the one of the man who slid along the entire length of his driveway.

The very act of walking is a balancing act we take for granted. "Walking is like falling and catching yourself over and over," says Kayla Lewis, Ph.D., an assistant professor of physics at New Jersey's Monmouth University. "You lean forward and fall forward, catching yourself with your leading leg to prepare for the next step. But it's the friction between the ground and your shoes that enables you to save yourself this way; it prevents your front shoe from sliding forward and your back shoe from sliding backward."

All of this begs the question: What's the best way to walk on ice to minimize the risk of falling? To safely sashay over ice, follow the experts' advice below. Don't let their words of wisdom, you know, slip away from you.

1. MOVE SLOWLY AND STEADILY.

Clearly, instinct and common sense kicks in the moment you approach the slick surface, telling us it's virtually impossible (and not really wise) to sprint across an ice-covered driveway. Slow and easy wins the proverbial race, right?

Yes. According to Philip E. Martin, Ph.D., professor and chair of the Department of Kinesiology at Iowa State University, minimizing forward and backward force is indeed essential when walking on ice. "What's key is trying to keep force applied to the ground more vertically so there's less force forward and backward—because that's the part that requires friction," he tells Mental Floss.

2. TAKE SHORTER STEPS.

What does reducing forward-and-backward force mean practically? Taking shorter steps. When we do so, the forces applied against the ground in forward and backwards directions are reduced. Therefore, Martin says, we're not pushing as hard and are "adapting our gait to work with the reduced friction that's available to us."

3. AVOID MELTING ICE.

Mark Fahnestock, a glaciologist and research professor at the University of Alaska Fairbanks, has been studying glaciers and ice sheets for the last couple of decades, and during that time has experienced conditions at -40°F in Alaska. He says that how slippery ice becomes can vary by temperatureso being aware of temperatures can help you figure out how easy or challenging it may be to cross ice. "It's easier to walk on ice at 0°F or -20°F," he tells Mental Floss. "Ice is much slipperier when it's really melting."

Chalk that up to a film of molecules on the surface that behaves like water, he says, which "becomes more pronounced" in warmer temperatures. However, this isn't to say you won't ever slip on ice the colder the temperature gets; he emphasizes, "It's not that it's not slippery, it's just that it's not as slippery as when it's warmer."

4. GO AROUND SLOPES AND STAIRS WHEN YOU CAN.

You should also be mindful of the surface you're about to set foot on. A flat surface is one thing, but Fahnestock says that "if it's slanted where your foot meets a driveway, for example, it's not holding your weight—rather, it's your weight that's causing your foot to move."

"Gravity is going to do its thing whether you like it or not," Martin says, especially if there's an icy slope that's in a significantly downhill direction. Unfortunately, in this circumstance, you probably won't be able to adapt your gait to prevent slipping, so it's likely it'll be a score of Ice 1, Human 0.

ice caution sign next to person who slipped on ice
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Stairs can make navigating ice even more treacherous, but we know it's not always possible to avoid them. According to helpful hints for walking on ice from Iowa State University, when dealing with icy steps, be sure to use handrails, keeping your hands out of your pockets, and continue to move slowly.

5. KEEP AN EYE OUT FOR CHANGING SURFACES.

Then there are circumstances where the surface characteristics can change without us realizing it. But Martin says not to fret if you're walking on a straight, dry surface and suddenly encounter an icy patch you weren't expecting. Maximum friction force is reduced when you encounter this abrupt change, causing you to quickly alter your gait. Sure, you may slip a little since it initially throws you off guard, but "humans are pretty adaptable and recognize challenges quickly," Martin says. We pay closer attention to surface characteristics than we may consciously realize, and we adjust our stride patterns automatically.

6. WEAR THE RIGHT SHOES.

And don't forget the benefits of appropriate footwear. Martin encourages people to consider a shoe's material properties, noting that a rigid leather sole is far from ideal as it offers a significantly weaker grip compared to a rubber sole. Of course, traction-improving treads, cleats, or spikes can help too.

Scientists are studying how traction varies among consumer boots. A team of researchers at iDAPT, the research arm of the Toronto Rehabilitation Institute—University Health Network, has tested and rated the slip resistance of nearly 100 boots and spikes in their WinterLab, where they study slips and falls on a floor composed entirely of ice. Testers secured into safety harnesses walk back and forth across the ice as the researchers slowly increase the angle of the floor until the tester slips. The angle at which they slip is called the "maximum achievable angle": The higher the angle, the better the slip resistance.

More than 80 percent of the boots they've tested failed to score high enough on the MAA to earn a single "snowflake" on iDAPT's three-snowflake scale, including those from popular brands like Timberland, Sorel, and Terra. The top ranked, with three snowflakes, are all Stabil spikes, which attach to your regular shoes or boot.

7. WHEN ALL ELSE FAILS, WADDLE.

Consider taking an ice-walking cue from those waddling tuxedoed ice pros: Walk like a penguin. Fahnestock says shuffling helps keep your weight in a straight-down stance, allowing your feet to carry your weight carefully and minimize slipping.

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