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Will My Phone's Battery Go On the Fritz in the Freezing Cold?

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This Big Question comes from a coworker who went jogging yesterday in freezing temperatures; his admirable act of temporary insanity left him with a dead phone for 10 minutes. Once he thawed out, he wanted to know whether or not it was normal for his smartphone to catch a cold.

On its website, Apple recommends you use its devices “where the ambient temperature is between 32° to 95°F.” (Sorry Minnesota, that important phone call will have to wait until April.) In covering their legal bases, Apple is likely being overcautious. While extreme cold—much colder than 32 degrees Fahrenheit—can cause your phone to go on the fritz, this problem has almost always proven to be a temporary one.

And what causes the brief blackout? According to David Linden and Thomas B. Reddy’s Handbook of Batteries, very cold temperatures will lower the “discharge capacity” of a lithium-ion battery (the kind of battery commonly used in smartphones). In other words, the battery struggles to perform efficiently in the cold and will drain faster. Still, this is only while in use, and the long-term effects aren’t too scary.

Seth Porges of Popular Mechanics took six types of smartphones to an environmental testing facility to gauge their performance in the extreme cold. They started with a slightly brisk environment (40°F) and then incrementally lowered the temperatures to points far below zero.

All the phones survived down to -10°F. Once the mercury hit -30, however, “five of the six phones experienc[ed] serious battery or LCD problems.” Reassuringly, none of the damage suffered during these tests proved to be permanent. Once the phones returned to normal temperatures, so did their functionality.

The only phone to survive a plunge to -40°F was an outdated Motorola flip phone, one whose high-tech features include texting and not much more. In fact, that same flip phone survived conditions that are positively Plutonian (-314.7°F). After repeatedly being dipped in liquid nitrogen, the phone would still perform fine after warming back up to a normal temperature.

Score one for the “they don’t make ‘em like they used to” crowd. Clip those flip phones to your belts with pride, friends, you earned it.

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Big Questions
What Causes Sinkholes?
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Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

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Big Questions
How Are Speed Limits Set?
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When driving down a road where speed limits are oppressively low, or high enough to let drivers get away with reckless behavior, it's easy to blame the government for getting it wrong. But you and your fellow drivers play a bigger a role in determining speed limits than you might think.

Before cities can come up with speed limit figures, they first need to look at how fast motorists drive down certain roads when there are no limitations. According to The Sacramento Bee, officials conduct speed surveys on two types of roads: arterial roads (typically four-lane highways) and collector streets (two-lane roads connecting residential areas to arterials). Once the data has been collected, they toss out the fastest 15 percent of drivers. The thinking is that this group is probably going faster than what's safe and isn't representative of the average driver. The sweet spot, according to the state, is the 85th percentile: Drivers in this group are thought to occupy the Goldilocks zone of safety and efficiency.

Officials use whatever speed falls in the 85th percentile to set limits for that street, but they do have some wiggle room. If the average speed is 33 mph, for example, they’d normally round up to 35 or down to 30 to reach the nearest 5-mph increment. Whether they decide to make the number higher or lower depends on other information they know about that area. If there’s a risky turn, they might decide to round down and keep drivers on the slow side.

A road’s crash rate also comes into play: If the number of collisions per million miles traveled for that stretch of road is higher than average, officials might lower the speed limit regardless of the 85th percentile rule. Roads that have a history of accidents might also warrant a special signal or sign to reinforce the new speed limit.

For other types of roads, setting speed limits is more of a cut-and-dry process. Streets that run through school zones, business districts, and residential areas are all assigned standard speed limits that are much lower than what drivers might hit if given free rein.

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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