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  • Hey, Vsauce. Michael here. And today, we're going to talk about water.

  • Because today is World Water Day. A day about raising awareness of the fact

  • that, even though, here on Earth, there is enough clean, safe, drinking water for everybody

  • to have enough, they don't. In fact, a billion of them don't.

  • But it doesn't have to be that way. Now first, I wanna cover how water is not

  • just vital and amazing, but to this day, continues to surprise us.

  • For instance, the Mpemba effect. The effect has been observed many many many

  • times, but has never been explained. In fact, it is so famously anti-common sense,

  • whenever people throughout history have observed it, they've tended to think that they just

  • did something wrong. Which is why even though Aristotle himself

  • wrote about it, it wasn't until the 20th century that it got its name.

  • Simply put, the Mpemba effect is the observation that under the right circumstances a glass

  • of boiling hot water inside a freezer can turn to ice more quickly than a glass of cold

  • water. It doesn't make a lot of sense, but it can

  • happen. A few possible causes have been thrown out.

  • For instance, if you heat up or boil water, you remove some of the dissolved gas.

  • And having less stuff dissolved in it may be what makes hot water easier to freeze.

  • It's the opposite of why we throw down salt during wintery weather.

  • The salt dissolves into the water, putting more stuff in it, making it more difficult

  • to freeze. But does that account for the entire effect?

  • Well, some other possible explanations involve convection currents.

  • A glass of warm water will contain more cycling convection currents, meaning that the top

  • of that glass of water is warmer. And a glass of warm water will tend to freeze

  • from the sides in, whereas the glass of cold water will tend to freeze all across the top

  • down. But once that top layer is frozen, it acts

  • as an insulator, so all the water below it freezes more slowly.

  • The point is that we still do not have a complete explanation of the effect.

  • Part of the problem is how difficult it is to control every single variable.

  • Should we be using equal masses of water or equal volumes?

  • Should they be in the same freezer or in separate freezers?

  • And what about evaporation? The warm water will be evaporating faster

  • and evaporations into thermosis, it's losing heat more quickly than the cold water.

  • It's tough. But here's what we do know.

  • Earth has a lot of water. 70% of Earth's surface is covered in it.

  • And, interestingly enough, excluding fat, the human body is about 70% water.

  • But when you were born you were a big old sack of water.

  • That's right. A new baby is 78% water.

  • Now, that number drops to 65% by the time that baby is 1 year old.

  • And it'll drop even further to about 60% when you're an adult... man.

  • Adult women are only about 55% water. This is because women's physiology on average

  • contains more fat, which doesn't hold as much water as lean tissue.

  • In fact, fat people, regardless of gender, contain less water than thin people.

  • Earth has a lot of water, but it's almost all salty.

  • 96.5% of the water on Earth is in the oceans. Another 3.4% of Earth's water can be found

  • in other large bodies of water or frozen inside glaciers or ice caps.

  • But you, me, all the other animals we see, other manufactured products?

  • They all contain water. About 0.0003% of Earth's total water.

  • And all of the storms and clouds and rain and thunderstorms happening contain only about

  • 0.0001% of all the water Earth has. That's a lot of water, but despite that fact,

  • almost a billion people on Earth don't have access to potable water.

  • Potable comes from the Latin for "to drink," which means clean, safe water free from disease

  • and contamination. The number of people on Earth who do not have

  • sustainable access to potable water is equivalent to the number of people living inside the

  • United States. Except multiplied by three.

  • And every year 3.5 million people die because of non-potable water-related diseases.

  • That's equivalent to the entire population of Los Angeles.

  • So every year, Earth, our planet, looses an entire city of Los Angeles because people

  • don't have access to clean water. So today, on World Water Day, it's worth talking

  • about organisations that are making a difference, because things don't have to be the way that

  • they are. Organisations like help local communities

  • build sustainable clean water solutions that the community itself will own.

  • Now, they gave me a chance to go out to India to see this in action, along with WheezyWaiter and Strawburry17.

  • Unfortunately, I wasn't able to go, but those

  • other two people were and they've got videos over on their channels about their experiences.

  • So go check those out and if you wanna learn more, got to see how you

  • can help.

  • And as always,

  • thanks for watching.

Hey, Vsauce. Michael here. And today, we're going to talk about water.


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水是驚人的 -- 世界水日 (Water Is Amazing -- World Water Day!)

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    林宜悉 發佈於 2021 年 01 月 14 日