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Noshin R, Flickr // CC BY 2.0
Noshin R, Flickr // CC BY 2.0

What Makes Pop Rocks Pop?

Noshin R, Flickr // CC BY 2.0
Noshin R, Flickr // CC BY 2.0

Eating most candy isn’t complicated: You take a bite, enjoy a sugar-fueled dopamine rush, and repeat until you have a stomach ache. Chemist William A. Mitchell added another step to the process when he developed Pop Rocks. When the sweet, hard candy bits hit your mouth, they act up before breaking down, creating a crackling, hissing noise that would be alarming coming from any other food product. But when it happens to Pop Rocks, you know you’re getting what you paid for. So what exactly is it about the candy that makes it just as much of a science experiment as a sweet snack?

The answer lies in carbon dioxide. It’s the same gas that gives cola, beer, and champagne their effervescence, but it’s not a common ingredient in solid foods. In the late 1950s, Mitchell wondered if it was possible to create an instant soda tablet by baking CO2 into candy. Even though his idea didn’t take off, the experiments laid the basis for Pop Rocks.

Like other hard candies, Pop Rocks are made by mixing sugar, lactose, corn syrup, and flavorings. Once those ingredients are melted together and boiled, highly-pressurized CO2 is added. When the candy mixture hardens, it traps bubbles of gas exerting pressure at 600 pounds per square inch (psi). For reference, the pressure inside a champagne bottle measures in at 90 psi.

It’s impossible to detect the special component in Pop Rocks unless you taste them. Magical things happen when the candy meets up with your mouth: As your saliva dissolves the sugar, those powerful air pockets begin to burst like miniature firecrackers on your tongue. The 600 psi carbon dioxide collides with the 15 psi pressure of the atmosphere, resulting in a crack you can feel and hear. That’s why Pop Rocks are so noisy, whether you’re eating them or standing next to someone who is.

And if you’re worried that all that pressure will do some serious damage to your body, you can rest easy. Contrary to the hysteria from kids and parents, there’s never been a known case of death by Pop Rocks. That includes when it's mixed with Coke (sorry Mikey truthers).

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Big Questions
Are There Number 1 Pencils?
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Almost every syllabus, teacher, and standardized test points to the ubiquitous No. 2 pencil, but are there other choices out there?

Of course! Pencil makers manufacture No. 1, 2, 2.5, 3, and 4 pencils—and sometimes other intermediate numbers. The higher the number, the harder the core and lighter the markings. (No. 1 pencils produce darker markings, which are sometimes preferred by people working in publishing.)

The current style of production is profiled after pencils developed in 1794 by Nicolas-Jacques Conté. Before Conté, pencil hardness varied from location to location and maker to maker. The earliest pencils were made by filling a wood shaft with raw graphite, leading to the need for a trade-wide recognized method of production.

Conté’s method involved mixing powdered graphite with finely ground clay; that mixture was shaped into a long cylinder and then baked in an oven. The proportion of clay versus graphite added to a mixture determines the hardness of the lead. Although the method may be agreed upon, the way various companies categorize and label pencils isn't.

Today, many U.S.  companies use a numbering system for general-purpose, writing pencils that specifies how hard the lead is. For graphic and artist pencils and for companies outside the U.S., systems get a little complicated, using a combination of numbers and letters known as the HB Graphite Scale.

"H" indicates hardness and "B" indicates blackness. Lowest on the scale is 9H, indicating a pencil with extremely hard lead that produces a light mark. On the opposite end of the scale, 9B represents a pencil with extremely soft lead that produces a dark mark. ("F" also indicates a pencil that sharpens to a fine point.) The middle of the scale shows the letters and numbers that correspond to everyday writing utensils: B = No. 1 pencils, HB = No. 2, F = No. 2½, H = No. 3, and 2H = No. 4 (although exact conversions depend on the brand).

So why are testing centers such sticklers about using only No. 2 pencils? They cooperate better with technology because early machines used the electrical conductivity of the lead to read the pencil marks. Early scanning-and-scoring machines couldn't detect marks made by harder pencils, so No. 3 and No. 4 pencils usually resulted in erroneous results. Softer pencils like No. 1s smudge, so they're just impractical to use. So No. 2 pencils became the industry standard.

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Big Questions
What Are Curlers Yelling About?
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WANG ZHAO/AFP/Getty Images

Curling is a sport that prides itself on civility—in fact, one of its key tenets is known as the “Spirit of Curling,” a term that illustrates the respect that the athletes have for both their own teammates and their opponents. But if you’re one of the millions of people who get absorbed by the sport once every four years, you probably noticed one quirk that is decidedly uncivilized: the yelling.

Watch any curling match and you’ll hear skips—or captains—on both sides barking and shouting as the 42-pound stone rumbles down the ice. This isn’t trash talk; it’s strategy. And, of course, curlers have their own jargon, so while their screams won’t make a whole lot of sense to the uninitiated, they could decide whether or not a team will have a spot on the podium once these Olympics are over.

For instance, when you hear a skip shouting “Whoa!” it means he or she needs their teammates to stop sweeping. Shouting “Hard!” means the others need to start sweeping faster. If that’s still not getting the job done, yelling “Hurry hard!” will likely drive the point home: pick up the intensity and sweep with downward pressure. A "Clean!" yell means put a brush on the ice but apply no pressure. This will clear the ice so the stone can glide more easily.

There's no regulation for the shouts, though—curler Erika Brown says she shouts “Right off!” and “Whoa!” to get her teammates to stop sweeping. And when it's time for the team to start sweeping, you might hear "Yes!" or "Sweep!" or "Get on it!" The actual terminology isn't as important as how the phrase is shouted. Curling is a sport predicated on feel, and it’s often the volume and urgency in the skip’s voice (and what shade of red they’re turning) that’s the most important aspect of the shouting.

If you need any more reason to make curling your favorite winter sport, once all that yelling is over and a winner is declared, it's not uncommon for both teams to go out for a round of drinks afterwards (with the winners picking up the tab, obviously). Find out how you can pick up a brush and learn the ins and outs of curling with our beginner's guide.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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