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Language: en

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I am taking this month off, and while I'm gone,

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five other YouTube creators have lined up
some brilliant guest videos for you.

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We start with science presenter, Steve Mould.

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And when he told me the title of this video
I thought,

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“No, I can't.”

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And then I was wrong.

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So: be nice, be kind; Steve, take it away!

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You have a super power that you’re probably
not aware of,

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the ability to hear temperature, or at least,

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the ability to discern between hot and cold
water just using your sense of hearing

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and this is something we can test.

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So, I’m going to pour hot and cold water
from these identical jugs

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into these identical mugs

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and it’s your job to figure out which is
which.

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And I’m going to blur the screen as well

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because there may be some visual cues that
would tip you off,

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one way or the other.

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Okay, here we go.

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It should have been quite easy to tell which
was which.

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Feel free to pause the video and leave a comment
with your guess, if you like,

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but here’s the answer: the first pour was
cold and the second pour was hot.

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And the reason they sound different is because
of the fact

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that the water is viscous -- or thick, if
you like,

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and the viscosity of water goes down when
you heat it.

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This is something that’s easier to see with
a liquid like honey.

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So, warm honey is more runny than cold honey,

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whereas, with water, it’s less visually
apparent.

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But when you pour water,

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the way it splashes into a cup is affected
by the viscosity.

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And this change in the splashing of the water
changes the sound that it makes

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because of various complex fluid dynamic reasons.

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What’s really interesting is this is knowledge
you already had

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due to a lifetime of hearing cold drinks and
hot drinks being made.

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And like many things, this is something that
you knew intuitively,

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even though it wasn’t something you were
aware of consciously.

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Go subscribe to Steve Mould’s channel!

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I would recommend his video on a self-pouring
liquid as being a good place to start.

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Next time, the tale of an engineering disaster.