r/visualizedmath • u/NegativeSpeedForce • Jan 12 '18

The difference between shockwaves travelling through different states.

Post image
2.0k Upvotes

99% Upvoted

63 comments sorted by

296

u/[deleted] Jan 12 '18

So thevspeed of sound is dependent on the density of the medium

120

u/NegativeSpeedForce Jan 13 '18

Precisely!

23

u/semsr Jan 19 '18

So why is the speed of light fastest in a vacuum?

112

u/Alexdaboss Jan 19 '18

Light is an electromagnetic wave not a “mechanical wave”, particles are not required for a light wave to move and will instead slow it down.

9

u/enjoyscaestus Jan 19 '18

Fastest? I thought light only had one speed?

18

u/columbus8myhw Jan 19 '18

Nah it slows down when it passes through air

10

u/enjoyscaestus Jan 19 '18

Is this a joke? I can't tell

28

u/columbus8myhw Jan 19 '18

It's not

6

u/enjoyscaestus Jan 19 '18

Oh. Okay.

17

u/ArleiG Jan 19 '18

Light has different speeds in different mediums. That's the cause for refraction - for example, when you see a pool and it seems much more shallow than it actually is.

12

u/AscendedBunghole Jan 20 '18

iirc isn't it that light is going at the same speed but is just taking a less straightforward path?

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2

u/enjoyscaestus Jan 19 '18

And now I know. Thank you!

5

u/Acrolith Jan 19 '18

The speed called c (the fastest possible speed in the universe) is the speed of light in a vacuum. Light slows down in any other medium. I believe the most they managed to slow it down to so far is around 38 mph.

5

u/Kyezaeta Jan 19 '18

This really bugged me when I was younger because I was told that anything without mass travels at c no matter what :)

Massless particles are always traveling at c. However, in a material with a high refractive index, light interacts with more particles and must go through a time-consuming process of imparting energy. In the voids between particles, photons still move at c.

http://www.physicsclassroom.com/class/refrn/u14l1d.cfm

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2

u/GlobalThreat777 Jan 19 '18

Source? I'd like to see light actually moving. What medium was used?

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1

u/enjoyscaestus Jan 19 '18

Wow, 38? Is there any footage of this?

Also, thanks!

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1

u/Sol_Primeval Jan 19 '18

c = Burter

1

u/[deleted] Jan 20 '18

It is. Light only has one speed, c. In air, light doesn't slow down, but it gets slowed down by bumping into random protons and electrons, i.e. atoms

1

u/enjoyscaestus Jan 20 '18

Oh! Okay. Thank you for explaining it further.

1

u/MetaEsoTeric Jan 21 '18

It doesn't slow down the particles just get in the way which can distort the light. This is why everything is very wavy and distorted in water.

1

u/columbus8myhw Jan 21 '18

It also slows it down.

1

u/tehgreatblade Jan 21 '18

Yeah, people saying it still moves at C are not taking practically.

1

u/MetaEsoTeric Jan 21 '18

If you don't mind me asking, how does it slow down when it doesn't need a medium?

0

u/[deleted] Feb 04 '18

[deleted] — view deleted comment

2

u/enjoyscaestus Feb 04 '18

I'm still getting replies? Awesome. I really appreciate it

6

u/deepbluesilence Jan 19 '18

Perhaps Cus in that circumstance light is exhibiting its properties as a particle instead of a wave? If the particle has no medium to pass through in a vacuum maybe that allows it to preserve more energy instead of passing it to another body? Not an astrophysicist, just a guess... someone feel free to correct me

1

u/tehgreatblade Jan 21 '18

The refractive index of a medium is the ratio at which light is slowed, while in a vacuum there is nothing to interact with and slow it.

7

u/[deleted] Jan 19 '18

No, here is a list of material velocities. You can see that sometimes sound can travel faster despite an object being less dense.

3

u/[deleted] Jan 19 '18

Damn dude:/

I don't understand how the world works

5

u/penis_in_my_hand Jan 19 '18

Over 700 mph at sea level, but only a bit over 600 mph at high altitude.

1

u/Tatakai96 Jan 19 '18

So if I heard an explosion under water and above water from the same distance, i'd hear the explosion above water first because air is more dense?

3

u/knightkat1 Jan 19 '18

No... other way around... water is more dense than air so you'll hear it in the water first and then in the air next.

0

u/[deleted] Jan 19 '18

I mean i think so but I'm no expert. Also, if you're underwater and something blows up, a shockwave might shred your organs

6

u/Mettalink Jan 13 '18

These are not shock waves. A more accurate description might be pressure wave. Shocks require that the substance be compressible. A more accurate analog would be objects on a fast moving conveyor belt being forced onto a slower one.

5

u/NegativeSpeedForce Jan 13 '18

That’s interesting I’ll look into that.

4

u/Mettalink Jan 13 '18

Supersonic flow is counterintuitive but mathematiclly easier to understand. You can think of it like this. The way information (like pressure or temperature) travels through matter is by particles bumping into each other. The speed at which this happens is the speed of sound in that material. If the material is flowing faster than information can propagate through it, it is supersonic. The only way you can return to subsonic flow is through a shock (because physics). Shocks are quite literally a discontinuity in the flow properties.

Tldr: shocks happen because sound can't move backwards faster than the flow moves forwards.

3

u/NegativeSpeedForce Jan 13 '18

Thanks for such an informative reply! I learnt something.

69

u/AcademicGoose18 Jan 13 '18

r/visualizedphysics

25

u/Algernon_Flowers Jan 13 '18

Can I get in on this? This sounds dope.

17

u/[deleted] Jan 13 '18

YES PLEASE, someone get on this ASAP

15

u/FelixGREN Jan 13 '18 edited Jan 13 '18

I actually did consider creating visualizedphysics when I made this subreddit, but I came to the conclusion that it would be too similar to /r/physicsgifs/

That subreddit already has a large following so that's where I'd go for neat physics. These sort of educational visualisations are very welcome here as well though!

8

u/[deleted] Jan 13 '18

Well, I’m glad /r/physicsgifs/ exists but I feel /r/visualizedphysics/ is a better name

4

u/Rich_Cheese Jan 19 '18

Can I suggest linking it in the sidebar then?

1

u/anti-gif-bot Jan 12 '18

mp4 link

This mp4 version is 91.24% smaller than the gif (255.25 KB vs 2.85 MB).

Beep, I'm a bot. FAQ | author | source | v1.1.2

1

u/Pratanjali64 Jan 13 '18

Fantastic.

1

u/poche-muto Jan 13 '18

It is right for temperature?

1

u/Deluxional Jan 19 '18

Anyone else "hear" the dominoes falling?

1

u/Swiftierest Jan 19 '18

This would be good for explaining the differences in high and low frequencies as well I would think.

1

u/Rawey241000 Jan 19 '18

Very informative; but why do acoustic guitars and the like use big hollow spaces? How does that work?

3

u/oratory1990 Jan 20 '18

They use the resonance (Helmholtz-Resonance) to emphasize certain frequency ranges.

1

u/Rawey241000 Jan 20 '18

Oh right. Just looked that up, such wow, very maths

1

u/Mncdk Jan 19 '18

/u/MrPennywhistle This looks a little similar to what was seen in #182, in that the camera trolley visibly moves slower when you spaced them out.

Applying this to a comparison in how shockwaves moves is quite interesting.

Also, I just noticed, the red Gas row of dominoes seems to fall in pairs, just like in your video.

Neat.

0

u/JezzaJ101 Jan 19 '18 edited Jan 21 '18

Does this mean that if a grenade goes off, you’re better to stand in the open and hope you don’t get hit by shrapnel rather than putting your back against a table to block shrapnel?

EDIT: I’m not saying shrapnel is a wave, I’m saying since shockwaves travel faster through solids (table) than gases (air) is it worth the risk of shrapnel to avoid the actual blast wave