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Help with Forensics

  1. Jul 21, 2006 #1
    Im am currently doing a physics experiment involving blood splatters.

    Results

    No. of drops No. of splatters
    2 114
    3 237
    4 337

    The drops were dropped in succession and I was hoping someone could help me describe what was going on. In note form thats what I think happens. (diameter of drop on the ground surface was within 1 or 2 mm of each other)

    No of splatters increased as more drops were dropped, more volume at base causing more ‘blood’ to be pushed aside for the incoming blood?

    Thanks for your help.
     
  2. jcsd
  3. Jul 22, 2006 #2

    Danger

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    Gold Member

    I must preface this with the warning that I'm quite inebriated at the moment, so I might be missing something. As far as I can see, since the surface wasn't specified, it's indeterminable. The distance between the blood drops can be a function of either how much the victim was bleeding, or how fast he/she was moving. Rapid movement would mean more distance between drops, but it should also result in 'teardrop shaped' elongated stains. That might not be evident on a carpet, but should be on a hard surface or grass. In the case of a carpet, though, you might be able to determine how fast someone was movng by gauging the footprint depths and spacing versus the known weight and leg length of that person. That's about all that I can offer for now. I'll check back tomorrow.
     
  4. Jul 22, 2006 #3

    andrevdh

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    Have you ever seen the famous high speed photograph of a crown like structure formed by a drop of milk falling into a container of milk? The crown has various little protrusions of milk forming upwards with little drops forming at their ends. The protrusions form a circular (crown like structure) around the point where the drop came onto the surface. The protrusions form arches outwards (maybe parabolas?). I have no solid backing for how these structures form, but if I had to guess I would think it is a result of collisions of waves formed in the liquid by the falling drop, or vibrations (which are essentially the same phenomena). As the amount of liquid increases the pool can support more vibrations, causing more protrusions to form.
     
  5. Jul 22, 2006 #4
    The drops were dropped from a dropper onto a hard surface (desk bench in the lab) vertically from height 1m.

    If that helps anyone. My mate is bringing his high speed camera round in the next couple of days so hopefully that can shed some light.

    Thanks for your help.
     
  6. Jul 23, 2006 #5

    andrevdh

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    Homework Helper

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