Forensics C

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Re: Forensics C

Post by pikachu4919 »

justgreene wrote:Can anyone refer me to a website to buy good quality plastics to test for density? I have beads but they seem to be inconsistent. For example some of the beads of HDPE float in 48% isopropyl alcohol, whereas others sink.
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Re: Forensics C

Post by Willows »

Where's a good place to get fibers and/or hairs for practice?
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Re: Forensics C

Post by pikachu4919 »

Willows wrote:Where's a good place to get fibers and/or hairs for practice?
Those are a lot easier to come by than plastics :lol: well what I did is that for fibers, I went to the local craft store, picked out fabrics that were 100% of those particular fibers (i.e. a 100% cotton, 100% wool, 100% silk, etc.—but NO MIXTURES!! THOSE'LL THROW YOU OFF!!) and asked them for 1-inch samples of each of them. They gave me most of them for free, but idk if craft stores in your area will do the same. As for hairs...I think you could literally just pick them off actual animals and people? It sounds gross but that's how I'd do it because honestly I don't think it's really worth ordering fancy, already-prepared slides with the stuff on them since you'll probably have to prepare your own slides at competition anyways 8-)
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Re: Forensics C

Post by Panda Weasley »

I have a plastics question. When I was in Crime Busters my 3 years ago we had plastics (last year my state didn't for some reason) and we were taught (as well as I can remember) to just put the samples in the liquids and see if they sink or float. This seems to be the typical way to do it, but I can't for the life of me remember what we did after we had that knowledge. :oops: Is there just a basic chart we compare results to? From reading previous posts in this thread I think that's the answer, but I'm still confused. Any help would be lovely! :D
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Re: Forensics C

Post by iwonder »

Panda Weasley wrote:I have a plastics question. When I was in Crime Busters my 3 years ago we had plastics (last year my state didn't for some reason) and we were taught (as well as I can remember) to just put the samples in the liquids and see if they sink or float. This seems to be the typical way to do it, but I can't for the life of me remember what we did after we had that knowledge. :oops: Is there just a basic chart we compare results to? From reading previous posts in this thread I think that's the answer, but I'm still confused. Any help would be lovely! :D
Yeah, so see if they sink or float (I recommend pushing them down into the liquid and seeing how they move, surface tension is a factor). Then you'll know if they're more or less dense than that liquid, compare the densities.
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Re: Forensics C

Post by vivian_t »

This is my first year doing Forensics so I'm a little bit unfamiliar with some of the topics and have a few questions to ask:
  • 1. What material should we learn for pollen and seed? Or basic information about plants will do?
    2. For the glass what will I expect the proctor to ask? Figure out what is the impact, (like tracks) which two pictures match, or a combination of both?
    3. What are some methods of achieving Qualitative Analysis efficiently? You see, I did mine by testing the powders first four times in the order of Iodine<HCl<H2O<NaOH then the remaining with Benedict's Solution and the Flame Test. I couldn't find any good charts, but I did find some that tells the properties/reactiviy of each powder and base my chart on those results. Either the list of powder are hard to distinguish because some of them have so many properties in common or I'm just making this harder on my self by making the least efficient chart lol.
Thanks and any help is appreciated! :D
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Re: Forensics C

Post by AlphaTauri »

1. In my three years of competing in Forensics, I only ever saw pollen/seeds on one test (and it wasn't a particularly good test...), so I honestly don't know. Because the rules specify something like 1-3 subtopics from part e(?), most event supervisors forego it in favor of the classics like fingerprints or blood spatters. If anyone's ever seen it done well on a test, post about it, because I have no clue what one should actually study for that section.

2. Glass is a bit more commonly tested. Off the top of my head, you could be asked the order in which several cracks in a piece of glass formed, which direction the glass was shattered from, or maybe even determining the type of glass via refractive index (Snell's Law).

3. For QA, everyone has their own method, but your ultimate goal is to do as few tests as possible on each powder, so that you can be the most efficient with your time. Personally I am an ardent supporter of doing flame tests first, as it positively IDs three powders -- four, if you can distinguish the deep orange of Ca(NO3)2 from the yellow-orange of sodium -- and classifies the rest into three distinct categories (sugars (2), sodium compounds (4), and things that don't burn (5)). These categories can then be split up and the powders ID'd much more easily because there are much fewer possibilities in each. I know a lot of people also do solubility first for similar reasons, but I don't really know the full chart for that since I've never done it that way.

Hope that helps!
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Re: Forensics C

Post by josephm »

It seems like Forensics is the division C equivalent to Crime Busters, but what are the main differences?
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Re: Forensics C

Post by josephm »

Also what's the best way to manage time? Should both partners work on one section at a time to finish it faster or should they split up to cover more at once? And what would be the most important sections to work on first? QA obviously but then what
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Re: Forensics C

Post by samlan16 »

josephm wrote:It seems like Forensics is the division C equivalent to Crime Busters, but what are the main differences?
This is how I put it to the middle schoolers I coach: in Crime Busters, you only light fibers on fire. In Forensics, you light everything* on fire. That pretty much means that you are now taking advantage of basic spectroscopy to identify your compounds. Also, there are no metals or liquids, physical evidence is more in depth, and you will be expected to learn how to read a mass spec.
josephm wrote:Also what's the best way to manage time? Should both partners work on one section at a time to finish it faster or should they split up to cover more at once? And what would be the most important sections to work on first? QA obviously but then what
Split up, but reconvene early enough to write the essay.
EDIT: It really depends on the test and your preferences, but do try to get Benedict's testing and chromatography done early enough to correct any problems that may arise.



*Except plastics.
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