This Is Not a Shockwave

Summary

The video explains the difference between a sonic boom and the vapor cones seen around supersonic aircraft. It describes how shock waves occur when an object travels faster than the speed of sound. In contrast, vapor cones are caused by rapid cooling and condensation of moisture when air expands over the convex surfaces of supersonic aircraft, not by shock waves or pressure spikes.

Takeaways

• 🔊 音爆不是通过视觉观察到的现象，而是由声波堆叠形成的压力波引起的。
• 📏 声速在空气中大约是每秒340米，但这会随着大气条件，主要是温度而变化。
• 🚀 当物体加速并最终赶上并叠加声波时，会形成一个薄而强烈的压力波。
• 🔬 施列林成像和阴影图可以通过光的折射来可视化冲击波。
• 💧 见到的水蒸气凝结现象是由于气温下降导致空气中的水蒸气凝结，而非冲击波。
• 🌡️ 气温的降低导致空气中的水蒸气饱和度增加，进而形成可见的水蒸气。
• ✈️ 所观察到的蒸汽锥是扩张扇的结果，这发生在超音速流经过物体（如飞机机翼）的凸角时。
• 🌪️ 扩张扇是当超音速流经过可以扩张的区域时发生的现象，与冲击波形成的压力增加和温度升高相反。
• 🛰️ 发现号航天飞机的发射视频展示了通过固体火箭助推器和航天飞机飞行甲板的凸角形成的蒸汽锥。
• 🌈 超过光速的冲击波（例如水中的电子移动速度超过光在水中的速度）可以通过光的畸变直接观察到。

Q & A

什么是音爆？

音爆是由于物体以超过声速移动时产生的冲击波。当物体的速度达到或超过声速（大约340米/秒），它会追上并压缩前方的声波，形成一个强烈的压力波，这就是音爆。

音速在不同条件下是否会改变？

是的，音速会随着大气条件的变化而变化，主要受温度的影响。在空气中，音速通常是约340米/秒，但这个速度会随着温度的不同而有所改变。

如何用斯勒林成像和阴影图来可视化冲击波？

斯勒林成像和阴影图是通过捕捉光线在高压空气中的折射来可视化冲击波的方法。例如，从枪中射出的子弹会形成自己的锥形冲击波，通过这些技术，我们可以看到冲击波通过光线的畸变直接显示出来。

视频中所说的“不是音爆的现象”是什么？

视频中提到的现象是由于空气中的水汽凝结成可见的水蒸气造成的，这通常是由于温度的急剧下降导致的。这种现象称为膨胀风扇（expansion fan），它在超音速流过凸起表面（如飞机机翼或舱盖）时发生。

为什么我们在正常情况下看不到冲击波？

冲击波本身是由空气分子碰撞形成的非常薄的压力波，宽度只有100到200纳米。由于这个宽度太小，肉眼在正常情况下无法直接看到冲击波。

在什么条件下我们可以看到膨胀风扇导致的水汽凝结？

当空气中的水汽因为空气温度急剧下降而达到饱和状态时，就会出现水汽凝结现象。这通常在飞机进行高攻角机动或超音速飞行时发生，空气在飞机翼后迅速扩张，导致温度下降和水汽凝结。

为什么冲击波会导致温度升高而不是降低？

冲击波是由于空气分子密集碰撞造成的压力波，这种碰撞导致能量转化为热量，从而使气温升高。因此，冲击波通常伴随着温度的上升，而不是下降。

航天飞机发射时为什么会看到水汽凝结？

在航天飞机发射时，视频中提到的1995年7月13日发射的发现号航天飞机就是一个例子。当空气流经其固体火箭助推器和飞行甲板的凸面时，会形成膨胀风扇，导致空气迅速扩张和冷却，从而使水汽凝结成可见的蒸汽锥。

飞机在低于超音速时为什么也会出现凝结现象？

即使在低于超音速的速度下，飞机在进行高攻角机动时也会导致空气迅速扩张，这种扩张会导致空气温度下降，进而导致水汽凝结。这种现象可以在飞机翼后或其他空气快速扩张的区域观察到。

视频中提到的光速冲击波是什么？

光速冲击波是由电子在水中以超过光在水中的速度运动时产生的。这种现象会产生类似于音爆的冲击波，但是是以光的形式。这种现象在某些高能物理实验中可以观察到。

Outlines

00:00

🔊声波与音爆的科学探索

本段落解释了音爆现象，指出人们常见的对于音爆的误解，并详细解释了声波的传播、音速的定义及其与大气条件的关系。通过对静止物体发出声波的分析，解释了物体加速时声波如何堆积，形成压力波和震波。此外，本段还介绍了利用斯克莱林成像和阴影图法直观观察震波的方法，以及通过温度降低导致的水蒸气凝结形成可见的水汽锥，而非震波。最后，解释了扩张波的概念，它是在超音速流动中，流体在凸角扩展区域内扩张时形成的，与震波相反的现象。

05:02

📺独家内容与支持渠道介绍

本段落介绍了作者在Nebula平台上提供的独家视频内容，包括对光的震波现象的解释和工程应用。强调了Nebula平台为频道提供的支持，如无广告观看、提前发布视频等优势，并特别提到了《787的疯狂工程》视频将作为一个近一小时的导演剪辑版在Nebula上发布。此外，还提到了通过订阅CuriosityStream来支持频道的同时，能以优惠价格获取Nebula和CuriosityStream的双重订阅服务，以及推荐了其他值得观看的视频内容。

Keywords

💡音爆

音爆是当一个物体以超过声音速度移动时产生的一种现象，这会导致声波累积形成压力波，进而产生一种强烈的声音。在视频中，作者首先澄清了观众可能对于音爆的误解，并解释了音爆的真正含义。通过比较音爆和视频中讨论的其他现象，帮助观众理解音爆的特点和成因。

💡声速

声速是声波在介质中传播的速度，通常在空气中大约是340米每秒，但这个速度会随着大气条件的变化而变化。视频中通过解释声速和物体移动速度的关系，来阐述声波如何随物体加速而累积形成音爆。

💡施列林成像

施列林成像是一种可视化震波和流体流动的技术，通过光的折射来显示空气中的压力变化。在视频中，此技术用于直观展示子弹超过声速时形成的锥形震波，帮助观众理解声波在超过声速物体周围如何累积。

💡水蒸气凝结

水蒸气凝结是当空气中的水蒸气因温度降低而转变为可见的水滴或冰晶的过程。视频中讨论了这一现象如何与展示的非音爆现象相关，即通过温度降低导致的水蒸气凝结，形成了可见的水蒸气锥，而不是由于音爆引起的。

💡扩张波

扩张波是指当超音速流动经过一个给予流体扩张空间的区域时产生的现象，特别是在凸角过渡区域。视频中解释了扩张波是如何在飞行器的凸面部位形成水蒸气锥的，这与音爆形成的机理完全不同，而是空气快速扩张和冷却的结果。

💡蒸汽锥

蒸汽锥是由于飞行器高速飞行时周围空气的快速扩张和冷却引起的，导致水蒸气凝结形成可见的锥状云。视频中通过多个例子展示了蒸汽锥的形成，特别是在讨论展开扇和蒸汽锥的区别时，强调了观察到的现象是由空气扩张而不是音爆引起的。

💡绝对湿度

绝对湿度是单位体积空气中所含水蒸气的质量。视频中讨论了绝对湿度与温度变化的关系，解释了为什么温度的降低会导致空气中的水蒸气凝结成可见的水滴或冰晶，形成蒸汽锥或云。

💡湿度

湿度是表示空气中水蒸气含量的量度，直接影响水蒸气凝结和蒸汽锥的形成。视频中提到，在不同湿度条件下，蒸汽锥的强度会有所不同，因为空气中水蒸气的含量决定了凝结成可见水蒸气的潜力。

💡光的折射

光的折射是指光线在通过不同密度介质的界面时速度发生变化，导致其传播方向发生改变的现象。视频中利用光的折射原理来解释如何通过施列林成像技术可视化震波，因为高压空气会导致光线折射，从而使震波变得可见。

💡超声速流动

超声速流动是指物体或流体以超过周围介质中声速的速度移动的情况。视频中探讨了超声速流动如何在飞行器的凸面部分产生扩张波和蒸汽锥，而这种现象与音爆不同，是由于空气的快速扩张和冷却导致的。

Highlights

Shock waves occur when an object travels faster than the speed of sound

When a moving object catches up to the sound waves it emits, the waves stack up and create a spike in pressure known as a sonic boom

Sonic booms create a thin, high-pressure band of air molecules colliding that human eyes normally can't see

High-speed cameras can capture shock waves through light distortion and refraction effects

What we see in the video is actually water vapor condensing due to a temperature drop, not a shock wave

Warm air holds more moisture than cool air - when temperature drops, water is forced out of the air

The vapor cones show rapid air expansion in convex areas, causing cooling and condensation

Expansion fans are the opposite of shock waves, causing cooling instead of heating

We can see shock waves from particles moving faster than light speed in water

Get full explanations & uses of these light shock waves in engineering on Nebula

Nebula has director's cuts of videos too long for YouTube, early uploads, and exclusive content

Sign up via CuriosityStream's discounted yearly plan to access Nebula and documentaries

See the full story of how the host quit his engineering job before even starting his YouTube channel

Learn about the origins and early days of the YouTube channel on the Genesis podcast

Check out other great video recommendations on the channel to continue exploring

Transcripts

this is not a sonic boom but a quick

search of google images will tell you

otherwise

image after image after image all

showing something that is not a sonic

boom

so if this is not a sonic boom what is

it

to answer that question we first need to

address what a sonic boom is shock waves

occur as a result of the maximum speed

of sound which is the speed pressure

waves can travel which we perceive as

sound

the speed of sound in air is around 340

meters per second but that does change

with atmospheric conditions primarily

temperature

so let's imagine a stationary object it

releases a sound wave periodically which

propagates out at 340 meters per second

these sound waves are just areas of high

pressure air traveling outwards

now when the object starts to accelerate

we can see that the distance between the

sound waves behind the object increases

and the distance between the sound waves

in front of the object decreases

the pressure waves can't travel any

faster than 340 meters per second and

the object is catching up with them and

when it does catch up with them

something weird happens the sound waves

begin to stack up on each other causing

a sudden spike in pressure this pressure

wave is incredibly thin it's just a thin

band of molecules colliding because they

can't get out of each other's way fast

enough

only 100 to 200 nanometers wide the

human eye can't see this under normal

conditions but that high pressure air

does distort light through refraction

and with the right tools we can use that

to visualize shock waves using schlarin

imaging and shadow graphs here you can

see the sound wave propagating out of

the gun when it's fired then the bullet

traveling faster than the speed of sound

bursts from the gun and catches up with

the sound wave while forming its own

conical shock wave

this is the only way we can see a shock

wave directly through light distortion

so if this is not a shock wave what is

it

what we are seeing here is water

condensing in the air because of a

temperature drop

water vapor in the air is typically

invisible we can only see water vapor

when the air is too saturated with water

to absorb any more we can achieve this

by increasing the water content in the

air like when we boil water and we can

see the water vapor rising from it or by

decreasing the temperature of the air

warmer air is capable of holding more

moisture so if we were at 100

absolute humidity the maximum amount of

water the air can hold at 30 degrees

there would be about 30 grams of water

vapor per meter cubed of air but if we

drop the air temperature to zero degrees

celsius the maximum amount of water

vapor that air could hold would be only

5 grams per meter cubed

when the air temperature drops like this

water is forced to come out of the air

and form visible water vapor like clouds

or these vapor cones

that's what we're seeing here a sudden

drop in temperature that forces water

out of the air but shock waves cause a

spike in pressure increases in pressure

cause an increase in temperature not a

decrease

and that's really why we aren't seeing a

shockwave we are seeing the exact

opposite of a shockwave we are seeing an

expansion fan

expansion fans occur when supersonic

flow travels over an area where the flow

is given space to expand in particular

convex corners like over the convex

curve of the canopy or after the

thickest part of the wing and that's

exactly where we see vapor cones form on

all of these videos my favorite example

of this is this video of the discovery

space shuttle launching on july 13 1995

carrying a communication satellite to

orbit we can see vapor cones as the air

travels over the convex corners of the

solid rocket booster and the shuttle's

flight deck in videos like this one of

the fa18 the vapor cone flickers in and

out of intensity as it travels through

areas of higher and lower humidity

that's why we don't always see a vapor

cone we can only see it in the right

conditions where that expansion of air

causes a high enough decrease in

temperature to force water out of

solution

so we aren't seeing a shock wave here we

are seeing the exact opposite an

expansion fan of course we can see

condensation like this occur well below

supersonic speeds like when high angle

of attack maneuvers cause rapid

expansions of air behind the wing but

there is a kind of shock wave we can see

a shock wave that occurs when something

travels faster than the speed of light

many of you will be looking at the

screen with a raised eyebrow right now

but what you are looking at right now

are shock waves of light caused by

electrons traveling faster than light in

water in the extended cut of this video

available exclusively on nebula i have

included an explanation of how exactly

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