droplet impacts

Bloodstain pattern analysis (BPA) is one of several forensic science specialities that can help determine what exactly came to pass on a scene of a violent crime. Technologies for it are evolving constantly, which leads to a higher degree of accuracy than in the past.

Eduard Piotrowski published a paper entitled “on the formation, form, direction, and spreading of blood stains resulting in blunt trauma at the head” in 1895. The various publications that followed did not lead to a systematic analysis the way we know today. Herbert Leon MacDonell advanced the research that eventually culminated in the 1971 publishing of “Flight Characterisics and Stain Patterns of Human Blood”. He went on to present the first formal training course for bloodstain pattern analysis.

Crime scene investigator Sherry Gutierrez put forth some general principles for the analysis of gunshot wounds in particular that roughly indicate what can be deduced from those. These are as follows:

  1. The amount of forward spatter (away from the shooter) is greater than the back spatter (towards the shooter).
  2. The velocity of the forward spatter is greater than the velocity of the back spatter.
  3. Both forward and back spatter have a lower velocity than the bullet. (The relationship of the velocities from high to low can therefore be visualised as bullet –> forward spatter –> back spatter.)
  4. Both forward and back spatter form a “cone” of mist. 
  5. The density of the fluid droplets from an impact to a fluid-containing structure decreases as the distance from the bullet impact increases.
  6. High velocity wounds to bone may cause bone to go both forward and backward alongside the spatter.
  7. The bullet exits in the direction opposite of the shooter.

Forward spatter usually travels farther than the back spatter in the same incident. It also holds a larger volume of blood that expresses as individual stains than the back spatter does. Targets may move with the direction of the projectile upon the moment of impact, so (for example) someone who was shot in the back may move forward. Similarly, if the target is located in a moving vehicle the wind and other circumstances may affect the forward and back spatter to a degree.

Bloodstain pattern analysis can also be made visual by documenting bloodstains at the scene of the crime and measuring the angles of impact that can lead every trajctory back to an ‘origin point’. Nowadays, computer programs are used to visualise these calculations further and create a 3D-model of the circumstances of the crime. An older method is called “stringing” and consists of attaching a coloured string to the point of impact and running it to the termination point (like the wall or floor). The convergences and crossing points of these strings can then be used for crime scene reconstructions.

mightylettuce  asked:

hELLo jeSS. IT ME. Can i request headcanons for Josuke, Joseph and Jotaro and how would they react if his s/o saves them from a fatal blow, but end up quite hurt themselves? ( love me some angst :^) )

lettuce why 

I hope these are okay!

Also: Brief descriptions of injury! You’ve been warned!

Josuke reacting to his s/o taking a severe blow intended for him

  • He wouldn’t have realised it was happening until he saw his partner’s body flying past him from the impact- the droplets of their blood lingering in the air. At first, he wouldn’t have even recognised them, thinking ‘No, that can’t have possibly been-’ and then he’d see their face, screaming his name in both fear and sheer agony. 
  • In the moment, he hasn’t yet understood that the shot was intended for him, the only thought he can process is that he needs to get to his s/o- and fast. There’s a rather blatant wedge of meat and bone missing from their shoulder, with the arm twisting the wrong way.
  • He’s biting his bottom lip so hard that the bruises are already visibly setting in through the skin, which itself is nearing the breaking point. He’s shaking, he knows that he can’t get to them and they’ve been blown too far out of his stand’s reach. You can almost see the anger radiating off him and god help whoever it was who caused the situation. 
  • He’ll do something extremely stupid and charge at the opposing stand user while taking all the blows they can throw at him to the face, body, and legs; doing so with the intent of murder. A blind rage that only comes from using an innocent person in a fight. 
  • It could go one of two ways; he really could beat them to within an inch of their life there and then or he’d beat and ‘fix’ them into the nearest object he can see to get them out of the way.
  • He’ll have Crazy Diamond out and ready before he’d even made it back to his s/o, probably with tears down his face by this point. He’d be clutching them to his chest, burying their face into his body as they were healed and sobbing into them while he watched the extent of their injury disappear. 
  • He’d only realise what they did for him as they regain consciousness and whisper “You can’t heal yourself, Josuke.” and he’d breakdown entirely, overcome with the guilt of him believing it was his fault <<Breakdown, Breakdown>>

Jotaro reacting to his s/o taking a severe blow intended for him

  • As a pretty observant person in battle, he can’t quite believe that he didn’t understand straight away why his partner had just covered the left hand side of his body with their own so suddenly; it only really clicked when their figure dropped to their knees, curled over their stomach and shaking.
  • Jotaro would call for Star Platinum’s The World just a second too late to stop the injury. Aware that he couldn’t do anything about his partner given the situation, he’d use the frozen time to push them out to the sidelines of the fight (Even if it meant they had to land with a thud)
  • He’s an experienced fight and understands that now it’s happened, he doesn’t have the time to worry about it because worrying will do no good and potentially just worsen the situation.
  • “Yare yare daze, I ought to be excited for the moment I get to pay you back for that, but now I’m just really pissed off.”
  • His beatdown of justice is going to be as swift as it is violent because he doesn’t have the time to waste anymore when he really needs to be contacting the Speedwagon Foundation to send an Emergency Helicopter out to him
  • He’ll have no other choice but to rip off his partner’s t-shirt to uses as a temporary bandage since they’d have already lost consciousness from the bloodloss but would drape his own coat around them to retain somebody heat and make them easier to carry 
  • He didn’t realise how uncomfortable having their blood over his hands would make him
  • He won’t speak a word throughout the entire ordeal once alone with his s/o, believing that it was because of his own naivety that they almost died and no amounts of “But I chose to do it!” or  “You had to live because no one else could defeat the stand user!” is going to convince him otherwise

Joseph reacting to his s/o taking a severe blow in his place 

  • In all honestly, it might have actually been Joseph’s fault. 
  • He’d be acting too arrogant or cocky in battle and his partner would have to deal with his mess. He’d piss off the wrong person at the wrong time and didn’t snap out of it quick enough to be on the defensive, which is where his quick-thinking s/o would stand in front and take the hit aimed for Joseph’s heart. Instead, it would hit into the side of his partner’s throat. 
  • Meaning that, if they were also a Hamon user, they wouldn’t be able to either cope with the pain or begin to heal their injury. And by this point, Joseph would probably be getting rusty with his own Hamon so wouldn’t be much help either. 
  • He’d realise just before the enemy’s attack was about to hit his s/o’s throat and what they were doing in front of him and he’d scream their name in attempt to make them stop or move or something– (Think of when he cried out Caesar’s name)
  • But of course, he’d catch them as they fell backwards into his arms and used what little Hamon he could on the injury to lessen the blow and hopefully slow the bleeding, even if my a minute fraction. Just enough to maintain consciousness to be able to apply pressure to their own wound while Joseph began the Beatdown
  • “Whoo~ Look at you Mr. Big Baddie over there, do you feel better after bringing in someone completely unrelated to the fight? You must feel good, what would your Granny say? Come here- let’s be friends!”
  • Being Speedwagon’s somewhat adopted grandchild, you can guarantee that he will demand the best medical care and that he will receive it 
  • Of course, he’d deny the fact that his s/o needed to intervene because even though the event should have humbled him, he’s a cocky youth at heart. But he’ll know that it was his actions that lead to it and that maybe it was time for him to grow up a bit more lest someone else gets hurt. 

If you dropped a water balloon on a bed of nails, you’d expect it to burst spectacularly. And you’d be right – some of the time. Under the right conditions, though, you’d see what a high-speed camera caught in the animation above: a pancake-shaped bounce with nary a leak. Physically, this is a scaled-up version of what happens to a water droplet when it hits a superhydrophobic surface. 

Water repellent superhydrophobic surfaces are covered in microscale roughness, much like a bed of tiny nails. When the balloon (or droplet) hits, it deforms into the gaps between posts. In the case of the water balloon, its rubbery exterior pulls back against that deformation. (For the droplet, the same effect is provided by surface tension.) That tension pulls the deformed parts of the balloon back up, causing the whole balloon to rebound off the nails in a pancake-like shape. For more, check out this video on the student balloon project or the original water droplet research. (Image credits: T. Hecksher et al., Y. Liu et al.; via The New York Times; submitted by Justin B.)


Drip food coloring into water and you can often see a torus-shaped vortex ring after the drop’s impact. That vortex rings form during droplet impact has been well known for over a century, but only recently have we begun to understand the process that leads to that vortex ring. Part of the challenge is that the vortex formation is very small and very fast, but recent work with x-ray imaging has allowed experimentalists to finally capture this event.

When a drop impacts a pool, surface tension draws some of the pool liquid up the sides of the drop. At the same time, the impact causes ripple-like capillary waves down the sides of the drop. This causes pool liquid to penetrate sharply into the drop, triggering the spirals that mark the forming vortex ring. When drops impact with even higher momentum, multiple vortex spirals can form, as seen on the lower right image. The authors observed as many as four rings during an impact. For more, check out the (open access) article.  (Image and research credit: J. Lee et al., source)


A drop of water that impacts a flat post will form a liquid sheet that eventually breaks apart into droplets when surface tension can no longer hold the water together against the power of momentum flinging the water outward. But what happens if that initial drop of water is filled with particles? Initially, the particle-laden drop’s impact is similar to the water’s – it strikes the post and expands radially in a sheet that is uniformly filled with particles. But then the particles begin to cluster due to capillary attraction, which causes particles at a fluid interface to clump up. You’ve seen the same effect in a bowl of Cheerios, when the floating O’s start to group up in little rafts. The clumping creates holes in the sheet which rapidly expand until the liquid breaks apart into many particle-filled droplets. To see more great high-speed footage and comparisons, check out the full video.  (Image credit and submission: A. Sauret et al., source)

effyeahjoebiden  asked:

So is the crown splash the curving wave of water on either side of the tire, the spikes of water in the middle behind the tire, or both? And is the Worthington jet also the same phenomenon that can happen with a massive meteorite impact?

Here the term “crown splash” refers to the curving sheets of water spreading on either side of the tire. Those liquid sheets (or lamella) break down at the edges into spikes and droplets just like the ones seen when a drop falls into a pool, which is the traditional source of the term “crown splash” because it resembles a crown.

And, yes, enormous meteor impacts can create Worthington jets (that column of fluid that pops up after a droplet impacts)! This is why some craters have peaks in the middle. There are actually some surprising similarities between meteor impacts and fluid dynamics.

(Image credits: S. Reckinger et al., original post)

The simple coalescence of a drop with a pool is more complicated than the human eye can capture. Fortunately, we have high-speed cameras. Here a droplet coalesces by what is known as the coalescence cascade. Because it has been dropped with very little momentum, the droplet will initially bounce, then seem to settle like a bead on the surface. A tiny film of air separates the drop and the pool at this point. When that air drains away, the drop contacts the pool and part–but not all!–of it coalesces. Surface tension snaps the remainder into a smaller droplet which follows the same pattern: bounce, settle, drain, partially coalesce. This continues until the remaining droplet is so small that it can be coalesced completely. (Image credit: Laboratory of Porous Media and Thermophysical Properties, source video)


I often receive questions about how fluids react to extremely hard and fast impacts. Some people wonder if there’s a regime where a fluid like water will react like a solid. In reality, nature works the opposite way. Striking a solid hard enough and fast enough makes it behave like a fluid. The video above shows a simulated impact of a 500-km asteroid in the Pacific Ocean. (Be sure to watch with captions on.) The impact rips 10 km off the crust of the Earth and sends a hypersonic shock wave of destruction around the entire Earth. There’s a strong resemblance in the asteroid impact to droplet impacts and splashes. Much of this has to do with the energy of impact. The asteroid’s kinetic (and, indeed, potential) energy prior to impact is enormous, and conservation of energy means that energy has to go somewhere. It’s that energy that vaporizes the oceans and fluidizes part of the Earth’s surface. That kinetic energy rips the orderly structure of solids apart and turns it effectively into a granular fluid. (Video credit: Discovery Channel; via J. Hertzberg)


When a droplet impacts a pool at low speed, a layer of air trapped beneath the droplet can often prevent it from immediately coalescing into the pool. As that air layer drains away, surface tension pulls some of the droplet’s mass into the pool while a smaller droplet is ejected. When it bounces off the surface of the water, the process is repeated and the droplet grows smaller and smaller until surface tension is able to completely absorb it into the pool. This process is called the coalescence cascade.


This high-speed video captures the impact of liquid droplets onto a granular surface. While there is some similarity to liquid-solid and liquid-liquid impacts, the permeability of the granular surface helps to “freeze” the splash rather quickly. Energy is dissipated in the initial impact, causing a splash of grains.  Then the surface tension, viscosity and inertia of the droplet compete in causing the deformations seen in the video. The deformation appears strongly dependent on the kinetic energy with which the droplet hits the surface (i.e. proportional to the height from which it is dropped). (Video credit: G. Delan et al)


I love science with a sense of humor. This video features a series of clips showing the behavior of droplets on what appears to be a superhydrophobic surface. In particular, there are some excellent examples of drops bouncing on an incline and droplets rebounding after impact. For droplets with enough momentum, impact flattens them like a pancake, with the rim sometimes forming a halo of droplets. If the momentum is high enough, these droplets can escape as satellite drops, but other times the rebound of the drop off the superhydrophobic surface is forceful enough to overcome the instability and draw the entire drop back off the surface.  (Video credit: C. Antonini et al.)


Icing is a major problem for aircraft.  When ice builds up on the leading edge of a wing it creates major disruptions in flow around the wing and can lead to a loss of flight control. One of the important factors in predicting and controlling ice building up is knowing when and where water droplets will freeze. The video above shows how surface conditions on the wing affect how an impacting droplet freezes. On a subzero hydrophilic surface, a falling droplet spreads and freezes over a wide area, which would hasten ice buildup. A hydrophobic surface is slightly better, with the droplet freezing over a smaller area, whereas a superhydrophobic surface shows no ice buildup. Unfortunately, at present superhydrophobic surfaces and surface treatments are extremely delicate, making them unsuitable for use on aircraft leading edges. (Video credit: G. Finlay)