Nuclear Bomb vs. Dirty Bomb: What's the Difference?

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The Quick Trick: If you're standing in an absolute wasteland amid thousands of corpses, it was a nuclear bomb. If you're standing in a normal city street amid a moderate amount of inconvenience, it was a dirty nuclear bomb.

The Explanation: Here is the primary difference: Nuclear bombs have, in the past 70 years, killed hundreds of thousands of people. Dirty nuclear bombs have, in all of human history, killed exactly no one—partly because they aren't terribly dangerous and partly because not one has ever been detonated.

Conventional nuclear weapons get their explosive power from either nuclear fission or fusion. The bombs dropped on Hiroshima and Nagasaki—the only nuclear weapons that have been used in warfare—were both fission bombs. Fusion bombs, sometimes called hydrogen bombs, are even more powerful—the U.S. once detonated a 15-megaton fusion bomb in a test. That's approximately 100 times more powerful than "Little Boy," the nuclear weapon dropped on Hiroshima that instantly killed 100,000 people. Most modern bombs combine fission and fusion: a small fission bomb is used to create heat adequate to fuel the
fusion.

Even with the physics know-how, the bombs require exceedingly rare isotopes of either plutonium or uranium. The process of getting the elements to the necessary isotope is known as enrichment, and enrichment is generally the stumbling block for nations looking to join the nuclear club. It was even a challenge for the U.S.: Almost 90 percent of the Manhattan Project's budget was spent enriching uranium.

In short, nuclear weapons are extremely difficult to make—and we hope they always will be. A dirty nuclear bomb, on the other hand, could be made by a reasonably smart 14-year-old with access to hospital equipment. Dirty bombs combine conventional explosives (say, dynamite) with radioactive materials (say, cesium, which is used in radiation treatment for cancer patients). Almost all scientists believe that even in the case of a well-designed dirty bomb, the explosive would cause much more damage than the radiation. The fact is there just aren't any acquirable materials radioactive enough to cause much fallout. And while it could be very expensive and inconvenient to clean up an urban area after a dirty bomb attack—that's about it. The difference between the two is that conventional nuclear weapons are infinitely more worrisome.

Dirty Secrets
The only recorded attempt to detonate a dirty bomb came in 1995, when Chechen rebels—who had been on the forefront of terrorism techniques since the Soviet Union's breakup—called reporters to say they'd planted a bomb in a Moscow park. Made of dynamite and cesium taken from a cancer treatment center, the dynamite might have killed people, but its cesium would have been just the equivalent of a few X-rays for those walking past the park. Regardless, the bomb was defused before it exploded.

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

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

This article has been updated for 2019.

Chimpanzees Bond by Watching Movies Together, Too

Windzepher/iStock via Getty Images
Windzepher/iStock via Getty Images

Scientists at the Wolfgang Kohler Primate Research Center in Germany recently discovered that, like humans, chimpanzees bond when they watch movies together, the BBC reports.

In the study, published in Proceedings of the Royal Society B, researchers stationed pairs of chimpanzees in front of screens that showed a video of a family of chimps playing with a young chimp. They found that afterward, the chimps would spend more time grooming and interacting with each other—or simply being in the same part of the room—than they would without having watched the video.

They gave the chimps fruit juice to keep them calm and occupied while they viewed the video, and they chose a subject that chimps have previously proven to be most interested in: other chimps. They also used eye trackers to ensure the chimps were actually watching the video. If you’ve ever watched a movie with friends, you might notice similarities between the chimps’ experience and your own. Drinks (and snacks) also keep us calm and occupied while we watch, and we like to watch movies about other humans. Since this study only showed that chimps bond over programs about their own species, we don’t know if it would work the same way if they watched something completely unrelated to them, like humans do—say, The Lion King.

Bonding through shared experiences was thought to be one of the traits that make us uniquely human, and some researchers have argued that other species don’t have the psychological mechanisms to realize that they’re even sharing an experience with another. This study suggests that social activities for apes don’t just serve utilitarian purposes like traveling together for safety, and that they’re capable of a more human-like social closeness.

The part that is uniquely human about this study is the fact that they were studying the effect of a screen, as opposed to something less man-made. The chimps in question have participated in other studies, so they may be more accustomed to that technology than wild apes. But the study demonstrates that we’re not the only species capable of social interaction for the sake of social interaction.

[h/t BBC]

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