Name: 乱流：物理学の偉大な未解決の謎の一つ - トマス・チョール (Turbulence: one of the great unsolved mysteries of physics - Tomas Chor)
Uploaded: 2021-01-14T08:10:50.000Z
Duration: 5 min 28 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

You're on an airplane when you feel a sudden jolt.

Outside your window nothing  seems to be happening,

yet the plane continues to rattle you and your fellow passengers as it passes through turbulent air in the atmosphere.

Although it may not comfort you to hear it,

this phenomenon is one of the prevailing mysteries of physics.

After more than a century  of studying turbulence,

we've only come up with a few answers for how it works and affects the world around us.

And yet, turbulence is ubiquitous, springing up in virtually any system that has moving fluids.

That includes the airflow in your respiratory tract.

And the coffee in your cup, as you stir it.

as are waves crashing along the shore and the gusts of plasma in our sun.

Understanding precisely how this  phenomenon works would have a bearing on so many  aspects of our lives.

Liquids and gases usually have  two types of motion:

a laminar flow, which is stable  and smooth;

and a turbulent flow, which is composed  of seemingly unorganized swirls.

The laminar flow of unruffled smoke  at the base is steady and easy to predict.

and the pattern of movement changes to something chaotic.

and turbulent flows have certain characteristics in common.

Rather, this means that turbulence  is very sensitive to disruptions.

A little nudge one way or the other will eventually turn into  completely different results.

That makes it nearly impossible  to predict what will happen,

even with a lot of information  about the current state of a system.

Another important characteristic of  turbulence is the different scales of motion  that these flows display.

Turbulent flows have many  differently-sized whirls called eddies, which are like vortices of  different sizes and shapes.

All those differently-sized eddies  interact with each other,

breaking up to become smaller and smaller

until all that movement is  transformed into heat,

in a process called the “energy cascade."

In every flowing liquid or gas there  are two opposing forces:

Inertia is the tendency of fluids  to keep moving,

Less viscous substances like water or air  are more prone to inertia,

which creates instabilities that  develop into turbulence.

We measure where a flow falls  on that spectrum

with something called the Reynolds number,

which is the ratio between a flow's  inertia and its viscosity.

the more likely it is that  turbulence will occur.

Honey being poured into a cup,  for example,

The same set up with water has a Reynolds  number that's closer to 10,000.

The Reynolds number is useful for  understanding simple scenarios,

For example, the motion of the atmosphere is significantly influenced

by factors including gravity and the  earth's rotation.

Or take relatively simple things  like the drag on buildings and cars.

We can model those thanks to many  experiments and empirical evidence.

But physicists want to be able to predict  them through physical laws and equations

as well as we can model the orbits  of planets or electromagnetic fields.

Most scientists think that getting there  will rely on statistics and increased computing power.

Extremely high-speed computer simulations  of turbulent flows

could help us identify patterns that could lead to a theory

that organizes and unifies predictions across different situations.

Other scientists think that the phenomenon is so complex

that such a full-fledged theory  isn't ever going to be possible.

because a true understanding of turbulence could have huge positive impacts.

That would include more  efficient wind farms;

the ability to better prepare for  catastrophic weather events;

or even the power to manipulate  hurricanes away.

And, of course, smoother rides  for millions of airline passengers.

Despite how difficult it is to explain turbulence mathematically,

Vincent Van Gogh was able to capture it with a sounding accuracy

in his iconic painting "The Starry Night".

Watch this video to learn more about the surprising man behind his masterpiece.