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  • - Hey, it's me Destin.

  • Welcome back to "Smarter Every Day."

  • As long as I've understood the physics,

  • I've wanted to visualize the Shock Wave

  • on the front of a super sonic bullet.

  • But the problem with doing this,

  • is you have to have access

  • to some pretty expensive optical hardware.

  • Which is why I'm pretty excited

  • about this giant 16" parabolic mirror.

  • Which is going to let us play around

  • with the speed of sound.

  • Let's go get "Smarter Every Day".

  • Okay, We're going to use a Schlieren Setup

  • to get these bullet images.

  • Here's how it works.

  • So we have the camera right here, right.

  • So this is a Phantom v2511.

  • We have a mirror way over there and the way we're doing that

  • is that we have a point source here.

  • So we're shining that light and it's spreading out;

  • and as it spreads out it hits this mirror,

  • and it bounces back and as it bounces back,

  • it comes down to a point.

  • One point right there

  • and we're cutting off half of that light.

  • Long story short it comes right here

  • flips back over goes into the lens.

  • If the air is less dense then light travels

  • through it faster.

  • If air is more dense light travels through it slower,

  • that causes the light to move or bend,

  • as it goes through different types of air;

  • and then we can detect those shadows

  • using this Schlieren Setup.

  • This is my buddy Coop.

  • He's gonna shoot through his own shop.

  • We're not gonna do this, you know

  • (cow mooing)

  • - I'm not shooting at his shop.

  • I think we're ready.

  • - On target.

  • - Three, Two, One.

  • Fire. (gunshot)

  • Whoo huhu

  • (gun clicks) - Weapon Clear.

  • - That's a big boom.

  • So let's see if we got it.

  • (laughing)

  • - [Male] Come here Coop

  • - [Destin] Oh Coop, come look at this.

  • (sound wave)

  • - [Male] Oh Cool

  • - [Destin] That's unbelievable.

  • Okay, so I'm gonna save that.

  • I like to guess where the shock waves come from.

  • The initial one looks like its coming off the bullet itself.

  • But then later there seems to be this weak one

  • that I'm guessing that reflected from the plywood table

  • that the mirror is sitting on.

  • Not really sure about that.

  • But then there's this stronger one that comes after that

  • and my guess for that one

  • is that it's coming off the concrete floor,

  • because it's more of a pure reflection.

  • Then later if you fast forward the video

  • you can see there's a very week shock wave coming across,

  • and my guess is that's coming from the muzzle itself.

  • I'm not sure on all these.

  • I canna have to extrapolate,

  • but that's kinda part of the fun.

  • Three, Two, One.

  • Fire. (gunshot)

  • (laughing)

  • (sound waves)

  • That's legit man.

  • Okay so we've dropped it to 28 thousand frames per second.

  • We're trying to get a really good single image.

  • Fire. (gunshot)

  • (coughing)

  • I actually put air in my lungs.

  • (sound waves)

  • This footage looks amazing.

  • But to understand exactly what we're looking at

  • why don't we build a little bitty model

  • with a bullet and a stick and talk about it here.

  • So lets imagine that we've got this bullet sitting here

  • and we've got circles emitting from the front.

  • As we move this thing watch what happens.

  • Those circles will stack up in the front

  • and they kind of relax in the back and they expand, right.

  • So that's a normal flight.

  • What happens if the velocity at which we move thing,

  • out runs those circles moving away?

  • Check this out.

  • As we start to out run it,

  • you'll notice that we this expansion in the back here

  • and it tapers down and we get this angle.

  • We get this, I don't know what you'd want to call it, right.

  • We've got a cone here.

  • What happens if we move forward even faster?

  • (whooshu)

  • That angle that we made there is even shallower or pointier.

  • That's called the Mach Angle

  • and people use that to measure the exact velocity

  • of a bullet traveling through air.

  • There's a simple equation.

  • The Mach number is equal to one over sine of that angle

  • and you can figure out how fast it's moving.

  • I use the circle illustration

  • because that's the way I was taught in my Aerodynamic book.

  • But if you look at the high speed imagery,

  • you can actually see circles

  • being formed at regular intervals.

  • I don't understand what they are, but they clearly there.

  • What we're about to do is what I've wanted to do

  • from the day I understood what Schlieren Imagery was.

  • We're going to shoot a Subsonic and a Supersonic round,

  • and we're going to compare the difference in the shock wave.

  • Coop, whatta we have?

  • - [Coop] So this is a 300 blackout.

  • - [Destin] If I understand correctly.

  • The whole point of this particular round

  • is to keep it Subsonic.

  • - Correct.

  • [Destin] This is a heavier bullet.

  • - This is a by 100 grains.

  • Almost twice the weight of this bullet here,

  • and so this bullet right here

  • you'll get somewhere around 1080 feet per second

  • at the muzzle.

  • Whereas this bullet right here

  • will give you somewhere in the neighborhood of 1500.

  • [Destin] Do you know what the sound of speed is?

  • - Yeah, it's like 12 something.

  • [Destin] I don't know.

  • We'll put it on the screen, right here.

  • That's the speed of sound.

  • So this one above the sound, that one's below.

  • All this is on purpose because that weapon

  • and that cartridge design was made specifically

  • because of these physics.

  • - So lets do Supersonic first.

  • - [Coop] Sure.

  • - Okay.

  • Three, Two, One.

  • Fire. (gunshot)

  • (sound waves)

  • This shock wave looks very similar to the 50 cal

  • with one major difference.

  • The angle is more Obtuse which indicates that the bullet

  • is traveling much slower.

  • So he's chambering a Subsonic round now

  • and so on the Schlieren we should see

  • a drastically different image.

  • Two, One.

  • (gunshot)

  • (sound waves)

  • It looks like, it looks like(laughing)

  • - [Coop] (laughing) I can make it, I can make it.

  • (sound waves)

  • - [Destin] Alright, so this is a Subsonic bullet.

  • So why I we seeing these little flickery things

  • on the side of the bullet?

  • That doesn't make a lot of sense to me.

  • So this what I always do in a situation like this.

  • I went looking for expert, which lead me to Dr. Kanistras.

  • A well respected aerodynamics professor

  • at University of Alabama in Huntsville.

  • One thing we saw on the Subsonic bullet

  • is we see, we didn't see that shock wave

  • but we saw these weird lines

  • out to the side of the bullet, you know.

  • - [Dr. Kanistras] What is the speed, when you say Subsonic?

  • - [Destin] It's about 10 percent less

  • than the speed of sound.

  • - You have Supersonic flow there.

  • It's a Normal Shock.

  • What you see there.

  • - [Destin] On a Subsonic bullet?

  • - Uh-huh, what is happening on a commercial aircraft?

  • It goes between point eight to one point two.

  • Even if you're flying Subsonic,

  • you have acceleration of the flow.

  • So you're reaching one point two.

  • - [Destin] What?

  • - Then you going back Subsonic.

  • - [Destin] So what you're saying is even though I have,

  • - [Dr. Kanistras] It's a Normal Shock.

  • - [Destin] I have a Subsonic bullet

  • but the speed of the air is Supersonic right there,

  • half way up the bullet.

  • So on this Subsonic bullet, those things I'm seeing,

  • you're saying that's Supersonic flow.

  • - That's right.

  • - [Destin] And it's because the air

  • has to move out of the way around the bullet.

  • So it has to accelerate.

  • - That's right, yeah

  • - [Destin] Really.

  • - So the flow accelerates, and creates a Normal Shock there.

  • - [Destin] It's because this particular bullet

  • is so close to the speed of sound.

  • - It reaches a transsonic speed,

  • which is point eight to one point two.

  • So even if it's not supersonic at this point,

  • at some point on the surface it will become Supersonic.

  • - [Destin] That's cool.

  • Thank you.

  • (laughs)

  • That's really cool.

  • Thank you for explaining that.

  • After this we decided to move closer to the mirror,

  • so we could see what the muzzle blast

  • (gunshot)

  • from the weapon itself look like.

  • (sound waves)

  • After that we moved the muzzle back about a foot

  • so we could see that transition period

  • (gunshot)

  • where that bullet pierces through the blast itself.

  • What's even more impressive

  • is each one of those tiny grains of propellant

  • had that visible shock wave

  • you could see associated with it.

  • (sound waves)

  • One more thing real quick, we took video of revolver.

  • It literally leaks shock waves out of the side.

  • But before I show you that

  • I want to say thank to the sponsor which is Audible.

  • Audible has been a partner for "Smarter Every Day" forever,

  • and I'm very grateful because I enjoy getting smarter

  • by listening to books as I drive.

  • This is like the perfect Brand match for me.

  • It helps me get smarter everyday.

  • You can get free book by going to audible.com/smarter

  • or text in the word "smarter" to 500 500.

  • I've a special book to recommend today.

  • It's called "THEM, Why we hate each other and how to heal,"

  • and it's by Senator Ben Sasse.

  • I steer really far away from politics at all times,

  • but this is not a political book.

  • It's about the things that are eroding away at our culture.

  • Things like loneliness

  • and the importance of your family support structure,

  • and how we need a scape goat;

  • and sometimes we get angry at other people.

  • when the problem is things that we are doing in own life.

  • It's a really good book.

  • So I highly recommend it.

  • I'm not quite done with it, but up to this point

  • it seems to be apolitical.

  • So check that out.

  • "THEM, why we hate each other and how to heal."

  • You ca get that by going to audible.com/smarter

  • or texting the word "smarter" to 500 500.

  • It's about how we can improve ourselves

  • by working on our communities around us.

  • I really like it,

  • and now definitive scientific proof

  • of why your hands should never leave the grip of a revolver.

  • One. (gunshot)

  • (sound waves)

  • One. (gunshot)

  • - Weapons clear.

  • - [Destin] That is the best video

  • I've probably ever participated in.

  • (sound waves)

  • Look at that, oh my goodness.

  • Okay, well I've a feeling we're going

  • to be doing something like this again.

  • Can you see us stopping at this?

  • - No.

  • - Okay.

  • - No way.

  • - Yeah , so there you go.

  • Feel free to subscribe to "Smarter Every Day"

  • if you're into this kind of thing.

  • If you're not, I don't know what's wrong with you (laughs).

  • That's amazing.

  • Alright, cool, thanks.

- Hey, it's me Destin.

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超スローモーションの衝撃波シャドウ(弾丸シュリーレン) - Smarter Every Day 203 (Shockwave Shadows in Ultra Slow Motion (Bullet Schlieren) - Smarter Every Day 203)

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    林宜悉 に公開 2021 年 01 月 14 日
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