@[100000925517665:2048:Kathryn Myronuk] writes:
"Shock waves sending shock waves around the world. Here's a useful article that covers shock waves through the history of how we see and study shock waves (what was it that Mach did, what can we do today)
My dad was a forensics engineer who studied fires and explosions. Along with interesting show & tell films for school, and 'interesting' dinner discussions (1), I picked up a few lessons as a layperson on detonations and shock waves.
A. You don't have a good intuition for these. The speed, size and energy involved aren't just more than usual, they're different. A sonic boom isn't just a loud noise, a detonation isn't just a fast fire or a flash fire. (It's a bit like how a tsunami isn't just a larger wave, or an avalanche isn't like a large snowball. These analogies aren't enough to show the difference.) An earthquake isn't just like a train rumbling by, or a car crashing into a wall.
B. They happen fast-- 6700+mph [3000+m/s]. This is in the hypervelocity realm, much faster than bullets (which themselves cause shock waves) or military projectiles. These are faster than sunset, or an eclipse moving by. This is the speed of an ordinary earthquake rupture along a fault, but slower than lightning, or meteors. Again, generally outside of experience or Spidey-sense.
C. When they hit, they hit hard, and we forget how much energy is involved (2). When shock wave hits it is like a ripple, but again not like your intuition. It is a ripple, but...
C1. A ripple hitting in 3D. It is a surface coming at you. (Like a gust of wind hitting the side of a truck all at once, or like being hit by 50 boxers simultaneously.)
C2. A ripple that's effectively instantaneous, passing through the body in less than a millisecond. The effect is concentrated, like the difference between being hit with the flat side vs the sharp side of a knife. Except it isn't like a knife in that a knife is a line of damage, a blast wave is a surface of damage that goes through you (imagine a badly designed portal or alien scanner sweeping across you).
C3. A ripple that's highly energetic, a sudden shock of overpressure and underpressure. Which means you're seeing ripples in materials that normally do not behave like liquids (concrete, structures, bone, bodies)
C4. Ripples that reflect (bounce) differently depending on what they hit. If you're between a wall and an explosion, the wall might fall away from you, but the pressure wave(s) that bounced back at you could do intense damage — much more than the initial wave passing through you. This can happen inside the body.
C5. Ripples that have different speeds depending on what they are passing through. It isn't just like a car accident where all of you moves at once, which is bad enough. With a shock wave, different tissues will move at different speeds and shear away from each other- think white matter and grey matter in the brain. The overpressure and underpressure will affect you at the boundaries of solids and liquids and gases, leaving compression, stretching, ripping, cavitation (bubbles) and more.
C6. Ripples that are dangerous in themselves, but also cause and carry hypersonic fragments and shards. (It's like how a tsunami is dangerous, but then if the tsunami carries debris it gets worse.) But even without fragments (and then the winds that knock you over, or fire, or falling objects) the blast wave by itself is dangerous.
D. Hollywood gives you the wrong idea because they always show explosions in slow motion (or they show a flash fire). They rarely want to get these right, because done realistically you can't see any of the special effects. We think an instantaneous change is unrealistic because we're not used to them.
E. In air they come straight at you: if there's glass between you and it, you want to be around a corner or two for protection *before* the explosion.
If you're less than a third of a mile (half a km) from the source, it's happening faster than you can start to react. An Olympic sprinter might take a first step or two at best.
F. Always bring in expert investigators to check on what happened. Take the airplane explosion in the article. It looked like there were multiple explosions. There was one explosion with shockwaves that rippled around the plane, coming together to look like additional blasts.
https://www.americanscientist.org/article/high-speed-imaging-of-shock-waves-explosions-and-gunshots
(1) one family classic was the Thanksgiving dinner conversation which included the line "... And then there was no body part left larger than this here cork." [Aka don't use open flames in an empty fuel transport boat.] It's funny now.
(2) my dad worked on a case where someone lost an eye after a tiny hearing aid battery was thrown in a campfire. It might not seem like much energy, but all at once it was like a tiny mortar, a small projectile nestled in a slightly larger cup. In tests he did these batteries could deform wire cages."
"Shock waves sending shock waves around the world. Here's a useful article that covers shock waves through the history of how we see and study shock waves (what was it that Mach did, what can we do today)
My dad was a forensics engineer who studied fires and explosions. Along with interesting show & tell films for school, and 'interesting' dinner discussions (1), I picked up a few lessons as a layperson on detonations and shock waves.
A. You don't have a good intuition for these. The speed, size and energy involved aren't just more than usual, they're different. A sonic boom isn't just a loud noise, a detonation isn't just a fast fire or a flash fire. (It's a bit like how a tsunami isn't just a larger wave, or an avalanche isn't like a large snowball. These analogies aren't enough to show the difference.) An earthquake isn't just like a train rumbling by, or a car crashing into a wall.
B. They happen fast-- 6700+mph [3000+m/s]. This is in the hypervelocity realm, much faster than bullets (which themselves cause shock waves) or military projectiles. These are faster than sunset, or an eclipse moving by. This is the speed of an ordinary earthquake rupture along a fault, but slower than lightning, or meteors. Again, generally outside of experience or Spidey-sense.
C. When they hit, they hit hard, and we forget how much energy is involved (2). When shock wave hits it is like a ripple, but again not like your intuition. It is a ripple, but...
C1. A ripple hitting in 3D. It is a surface coming at you. (Like a gust of wind hitting the side of a truck all at once, or like being hit by 50 boxers simultaneously.)
C2. A ripple that's effectively instantaneous, passing through the body in less than a millisecond. The effect is concentrated, like the difference between being hit with the flat side vs the sharp side of a knife. Except it isn't like a knife in that a knife is a line of damage, a blast wave is a surface of damage that goes through you (imagine a badly designed portal or alien scanner sweeping across you).
C3. A ripple that's highly energetic, a sudden shock of overpressure and underpressure. Which means you're seeing ripples in materials that normally do not behave like liquids (concrete, structures, bone, bodies)
C4. Ripples that reflect (bounce) differently depending on what they hit. If you're between a wall and an explosion, the wall might fall away from you, but the pressure wave(s) that bounced back at you could do intense damage — much more than the initial wave passing through you. This can happen inside the body.
C5. Ripples that have different speeds depending on what they are passing through. It isn't just like a car accident where all of you moves at once, which is bad enough. With a shock wave, different tissues will move at different speeds and shear away from each other- think white matter and grey matter in the brain. The overpressure and underpressure will affect you at the boundaries of solids and liquids and gases, leaving compression, stretching, ripping, cavitation (bubbles) and more.
C6. Ripples that are dangerous in themselves, but also cause and carry hypersonic fragments and shards. (It's like how a tsunami is dangerous, but then if the tsunami carries debris it gets worse.) But even without fragments (and then the winds that knock you over, or fire, or falling objects) the blast wave by itself is dangerous.
D. Hollywood gives you the wrong idea because they always show explosions in slow motion (or they show a flash fire). They rarely want to get these right, because done realistically you can't see any of the special effects. We think an instantaneous change is unrealistic because we're not used to them.
E. In air they come straight at you: if there's glass between you and it, you want to be around a corner or two for protection *before* the explosion.
If you're less than a third of a mile (half a km) from the source, it's happening faster than you can start to react. An Olympic sprinter might take a first step or two at best.
F. Always bring in expert investigators to check on what happened. Take the airplane explosion in the article. It looked like there were multiple explosions. There was one explosion with shockwaves that rippled around the plane, coming together to look like additional blasts.
https://www.americanscientist.org/article/high-speed-imaging-of-shock-waves-explosions-and-gunshots
(1) one family classic was the Thanksgiving dinner conversation which included the line "... And then there was no body part left larger than this here cork." [Aka don't use open flames in an empty fuel transport boat.] It's funny now.
(2) my dad worked on a case where someone lost an eye after a tiny hearing aid battery was thrown in a campfire. It might not seem like much energy, but all at once it was like a tiny mortar, a small projectile nestled in a slightly larger cup. In tests he did these batteries could deform wire cages."