Turbulence: one of the great unsolved mysteries of physics - Tomás Chor
-
0:07 - 0:11You’re on an airplane
when you feel a sudden jolt. -
0:11 - 0:13Outside your window nothing
seems to be happening, -
0:13 - 0:17yet the plane continues to rattle
you and your fellow passengers -
0:17 - 0:21as it passes through turbulent air
in the atmosphere. -
0:21 - 0:24Although it may not comfort
you to hear it, -
0:24 - 0:28this phenomenon is one of the
prevailing mysteries of physics. -
0:28 - 0:31After more than a century
of studying turbulence, -
0:31 - 0:34we’ve only come up with a few
answers for how it works -
0:34 - 0:37and affects the world around us.
-
0:37 - 0:39And yet, turbulence is ubiquitous,
-
0:39 - 0:44springing up in virtually any system
that has moving fluids. -
0:44 - 0:47That includes the airflow
in your respiratory tract. -
0:47 - 0:50The blood moving through your arteries.
-
0:50 - 0:53And the coffee in your cup,
as you stir it. -
0:53 - 0:55Clouds are governed by turbulence,
-
0:55 - 1:01as are waves crashing along the shore
and the gusts of plasma in our sun. -
1:01 - 1:04Understanding precisely how this
phenomenon works -
1:04 - 1:08would have a bearing on so many
aspects of our lives. -
1:08 - 1:09Here’s what we do know.
-
1:09 - 1:13Liquids and gases usually have
two types of motion: -
1:13 - 1:16a laminar flow, which is stable
and smooth; -
1:16 - 1:21and a turbulent flow, which is composed
of seemingly unorganized swirls. -
1:21 - 1:24Imagine an incense stick.
-
1:24 - 1:30The laminar flow of unruffled smoke
at the base is steady and easy to predict. -
1:30 - 1:31Closer to the top, however,
-
1:31 - 1:34the smoke accelerates, becomes unstable,
-
1:34 - 1:38and the pattern of movement changes
to something chaotic. -
1:38 - 1:40That’s turbulence in action,
-
1:40 - 1:45and turbulent flows have certain
characteristics in common. -
1:45 - 1:49Firstly, turbulence is always chaotic.
-
1:49 - 1:51That’s different from being random.
-
1:51 - 1:55Rather, this means that turbulence
is very sensitive to disruptions. -
1:55 - 1:58A little nudge one way or the other
-
1:58 - 2:02will eventually turn into
completely different results. -
2:02 - 2:05That makes it nearly impossible
to predict what will happen, -
2:05 - 2:10even with a lot of information
about the current state of a system. -
2:10 - 2:12Another important characteristic of
turbulence -
2:12 - 2:17is the different scales of motion
that these flows display. -
2:17 - 2:21Turbulent flows have many
differently-sized whirls called eddies, -
2:21 - 2:26which are like vortices of
different sizes and shapes. -
2:26 - 2:29All those differently-sized eddies
interact with each other, -
2:29 - 2:31breaking up to become smaller and smaller
-
2:31 - 2:35until all that movement is
transformed into heat, -
2:35 - 2:38in a process called the “energy cascade."
-
2:38 - 2:41So that’s how we recognize turbulence–
-
2:41 - 2:43but why does it happen?
-
2:43 - 2:47In every flowing liquid or gas there
are two opposing forces: -
2:47 - 2:49inertia and viscosity.
-
2:49 - 2:52Inertia is the tendency of fluids
to keep moving, -
2:52 - 2:54which causes instability.
-
2:54 - 2:57Viscosity works against disruption,
-
2:57 - 3:00making the flow laminar instead.
-
3:00 - 3:02In thick fluids such as honey,
-
3:02 - 3:05viscosity almost always wins.
-
3:05 - 3:10Less viscous substances like water or air
are more prone to inertia, -
3:10 - 3:14which creates instabilities that
develop into turbulence. -
3:14 - 3:17We measure where a flow falls
on that spectrum -
3:17 - 3:20with something called the Reynolds number,
-
3:20 - 3:24which is the ratio between a flow’s
inertia and its viscosity. -
3:24 - 3:26The higher the Reynolds number,
-
3:26 - 3:29the more likely it is that
turbulence will occur. -
3:29 - 3:32Honey being poured into a cup,
for example, -
3:32 - 3:35has a Reynolds number of about 1.
-
3:35 - 3:40The same set up with water has a Reynolds
number that’s closer to 10,000. -
3:40 - 3:43The Reynolds number is useful for
understanding simple scenarios, -
3:43 - 3:47but it’s ineffective in many situations.
-
3:47 - 3:51For example, the motion of the atmosphere
is significantly influenced -
3:51 - 3:55by factors including gravity and the
earth’s rotation. -
3:55 - 4:00Or take relatively simple things
like the drag on buildings and cars. -
4:00 - 4:04We can model those thanks to many
experiments and empirical evidence. -
4:04 - 4:09But physicists want to be able to predict
them through physical laws and equations -
4:09 - 4:14as well as we can model the orbits
of planets or electromagnetic fields. -
4:14 - 4:18Most scientists think that getting there
will rely on statistics -
4:18 - 4:20and increased computing power.
-
4:20 - 4:24Extremely high-speed computer simulations
of turbulent flows -
4:24 - 4:28could help us identify patterns that could
lead to a theory -
4:28 - 4:33that organizes and unifies predictions
across different situations. -
4:33 - 4:37Other scientists think that the phenomenon
is so complex -
4:37 - 4:42that such a full-fledged theory
isn’t ever going to be possible. -
4:42 - 4:44Hopefully we’ll reach a breakthrough,
-
4:44 - 4:48because a true understanding of turbulence
could have huge positive impacts. -
4:48 - 4:51That would include more
efficient wind farms; -
4:51 - 4:54the ability to better prepare for
catastrophic weather events; -
4:54 - 4:58or even the power to manipulate
hurricanes away. -
4:58 - 5:03And, of course, smoother rides
for millions of airline passengers.
- Title:
- Turbulence: one of the great unsolved mysteries of physics - Tomás Chor
- Speaker:
- Tomás Chor
- Description:
-
View full lesson: https://ed.ted.com/lessons/turbulence-one-of-the-great-unsolved-mysteries-of-physics-tomas-chor
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. What exactly is turbulence, and why does it happen? Tomás Chor dives into one of the prevailing mysteries of physics: the complex phenomenon of turbulence.
Lesson by Tomás Chor, directed by Biljana Labovic.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:05
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