Salt Won't Help Your Water Boil Faster
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As they say, "a watched pot never boils" (actually, that was Benjamin Franklin). If you want your water to boil faster, just add some salt. Right? Nice try, but no: the notion that salt boils your water faster is an old wives' tale. Not only does it not help, it hurts, since salt actually has the opposite effect on boiling water.
Hot Water Can Freeze Faster Than Cold Water, And We Don't Know Why
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Sometimes, hot water freezes faster than cold water. It goes against everything you might assume, but it's true—minds as great as Aristotle, Descartes, and Francis Bacon have described it happening. The counterintuitive phenomenon didn't come to the attention of modern science, however, until a 13-year-old Tanzanian student named Erasto B. Mpemba noticed it himself while making ice cream. Because he was in a rush to get his ice cream in the freezer before other students had taken up all the space, Mpemba decided to put his boiling milk in without letting it cool first. Surprisingly, he found that his milk froze long before anyone else's. Mpemba asked his teachers why this might be, and most told him he must be mistaken. But a visiting physics professor named Dr. Denis Osborne thought about his question and asked a lab technician to test Mpemba's claim. Sure enough, hot water froze faster than cold in experiment after experiment, and in 1969, Osborne and Mpemba published a paper about the phenomenon. Even several decades later, scientists still struggle to explain the mechanism behind the Mpemba effect. The effect doesn't happen every time, making it difficult to study. The most popular hypothesis is that hot water evaporates more quickly, so it loses more mass and needs to lose less heat to freeze. But scientists have observed the Mpemba effect in closed containers with no evaporation. Supercooling, the idea that dissolved gases in the water might speed the freezing process, is also a possibility. In 2013, the media claimed that a team of researchers from Singapore had found the answer: the bonds between molecules in boiling water are more flexible and ready to give up energy (in the form of heat) than those in cool water. Unfortunately, scientists don't find their explanation as airtight as the public does. Learn more about the states of water with the videos below.
You Can Tell Whether Poured Water Is Hot Or Cold
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In 2014, NPR posed a challenge to its audience: if they listened to clips of hot and cold water being poured into glasses, could they tell which was which? The test was inspired by a similar one performed by British sensory-branding company Condiment Junkie, and the results were the same in both cases: overwhelmingly, people could tell which was which. In the NPR test, 80% of people correctly guessed the cold clip and 90% correctly guessed the hot clip. (Try the test yourself by watching the first video below). It all comes down to water's viscosity. Cold water is more viscous than hot water, which means that its molecules more readily cling to one another. This makes it relatively sticky, enabling it to bead on a windshield or stick in the bottom of a straw. When water is heated, the water molecules begin to move around much more rapidly, keeping them from clinging together and making the water runnier—that is, less viscous. Water with less viscosity will splash in smaller particles, and smaller particles create a higher pitch when they hit the glass. Explore the science of water temperature with the videos below.
Thermostat Temperatures Were Designed For Men
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In many homes and offices, men and women are in a constant battle over the thermostat. A 2015 paper published in the journal Nature Climate Change pointed out the reason why: the model that defined the standard thermostat temperature of 71º F (22º C) was designed in the 1960s and based on the metabolic rate of a 154 lb (70 kg), 40-year-old man. This underestimates women's metabolic rate by up to 35%, which could explain why women prefer a temperature quite a bit higher: 77º F (25º C), according to one study. The authors of the Nature paper point out that if standards were to take more genders, ages, and body types into account, the benefits would go far beyond making people comfortable. We could save energy and reduce carbon emissions, too. Explore thermostat science with the videos below.
You Don't Lose The Most Heat Through Your Head
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Here's a seasonal myth that belongs with "cold weather gives you colds" (it doesn't) and "you can't sunburn on a cloudy day" (you certainly can): You don't lose most of your body heat through your head. This myth is thought to have stemmed from a test the U.S. military performed in which subjects wore Arctic survival suits in winter weather. Because their heads were the only parts of their bodies left uncovered, that's where they lost most of their heat. Sounds like a good way to conclude that you lose most of your heat through your head, but not so fast: if the subjects had worn hats and left an equivalent area of their arms or legs uncovered, the same amount of heat would have escaped through those areas. The reason it feels like more heat escapes through some places than others is that your head, face, neck, and chest are up to five times more sensitive to temperature changes than the rest of your body. By bundling up with a hat and scarf in winter or taking off a ball cap in summer, you feel like you're doing more to change your body temperature than if you were to change other clothing. In reality, roughly 10% of your body heat escapes through your head, which just so happens to be the percentage of your body's surface area that your head makes up. Whether you wear a hat or not, the other clothes you wear have just as much of a role in how hot or cold you feel.