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Forensic Physical Science Exercises. Math-Science Partnership Workshop Maryville College-Pellissippi State July 07 – 11, 2008. Reasons for Forensics.

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Forensic Physical Science Exercises

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Forensic Physical Science Exercises

Math-Science Partnership Workshop

Maryville College-Pellissippi State

July 07 – 11, 2008


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Reasons for Forensics

  • With the popularity of CSI and other television, students have a strong interest in forensics. Even though these TV dramas are not often scientifically factual, they can keep students interested in learning science, even difficult concepts in physics, chemistry, and biology

  • Recognizing this, Vernier’s new book is called forensic science experiments and tries to build on this student interest.


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Vernier Forensic Experiments

  • We will do two experiments from the Vernier Forensics with Computers book.

    • No Dumping (available on their website for free) Forensic soil analysis

      • pH

      • Conductivity

      • Color and Absorptivity

    • Bouncing Back – using the motion detector to determine the contents of a closed cardboard box – analogous to ground penetrating radar


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Forensic Soil Analysis

  • Soil is one of the a few forensic samples that can be individualized if all the physical and chemical properties are used.

  • Typical analyses include:

    • Geological (mineral) composition

    • Soil profile by color

    • Soil density column

    • pH, conductivity determination

    • soil water absorbency


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Soil Water Suspension


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Soil pH Determination


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Soil Conductivity


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Soil Water Absorbency


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Forensic Analysis Data Sheet


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Questions to Ponder

  • What chemicals would affect the soil pH and conductivity as you determined it?

  • Why would different soils absorb water differently? What components would absorb the most water? Which would you expect to least absorbent?

  • Density tubes can be used to separate soil samples to compare them. How would you go about preparing a density tube?


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Bouncing Back Exercise

Using the motion detector to identify the location and size of a “buried” object in a cardboard box


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Basic Principles

  • The Vernier motion detector is a sonic locator that bounces sound waves off and object to determine its location in much the same way that a radar gun works in baseball or on the highway.

  • The sonic energy will partially penetrate a cardboard box. If the detector is slid along a ruler from one side of the box to the other, the contents of the box can be determined in much the same way that GPR or ground penetrating radar can locate buried objects, like bodies.


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Design of the Experiment

Record the distance versus position on the ruler, then move the ruler to a new position and then slide it again and record

Slide at constant rate along the ruler

Motion Detector

Motion detector

Ruler

Short distance

Longer distance

object


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Results

  • Determine how you will divide up the box surface and how many transits you want to make to be sure that you detect the object.

  • Plot the data in a way that will allow you to demonstrate where the object is in the box and the approximate dimensions of the object.

  • Be prepared to explain what you found to the class. You may want to think of a way to interpret your transit data for the class, explaining the principle behind the probe you used.


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Variables

  • This experiment works well in class if you use an object with a strong “sonic profile” and an object made of pretty dense material like metal. You can prepare several boxes (or crime scene fields to keep the analogy pure) and see who in your class can both find the object AND explain the science behind how they were able to locate and identify it.


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