Introduction: By examining the size and shape of blood spatter, forensic scientists are able to reconstruct a crime. A partial story of a crime emerges as bloodstain analysis starts to tell a story



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Blood-Spatter Analysis: Effect of Height on Blood Drops
Introduction: By examining the size and shape of blood spatter, forensic scientists are able to reconstruct a crime. A partial story of a crime emerges as bloodstain analysis starts to tell a story. The police need to know the size and shape that blood creates when dropped from various heights. They can then use this information to solve a crime.
Objectives:


  1. Compare and contrast the blood spatter produced from different heights.

  2. Distinguish between blood drops formed at the point of contact with satellite blood droplets.

  3. Form a hypothesis about the effect of height on the size and shape of blood-spatter droplets.


Procedure:

  1. Spread newspaper on the work area.

  2. Obtain a bottle of fake blood and a piece of mural paper approximately 1 m in length.

  3. Label each section of your mural paper for the ten different heights indicated in the table below.

  4. Using the bottle of fake blood, drop one droplet from the first height (10 cm) indicated in the table below into the section of your mural paper labeled for that height. Use the meter stick to measure the heights from which you will drop the blood. With the help of your partner, hold the meter stick vertically for measurement and squeeze out one drop of blood from 10 centimeters(cm). Hold your hand steady and slowly release the one drop of blood.
  5. Repeat this process two more times at a height of 10 cm. Use the same area of the mural paper, but make sure your drops do not land on each other.


  6. Repeat steps 4-5 for the rest of the heights.

  7. Once the drops are dry, measure the diameter of each of the spatter patterns and record this data in the table. Take your measurements at the widest part of the main drop. Do not include the spikes or satellites in your measurement.

  8. Determine the average diameter for the blood spatter of each height and record it in your table.

  9. Prepare a graph using a program such as Excel™ comparing the average diameter for each height. Your graph should contain a title and labeled axes. Graphs must be printed out and stapled to this sheet!




Height of drop (cm)

Diameter of drop 1


(mm)

Diameter of drop 2

(mm)

Diameter of drop 3 (mm)

Average diameter


(mm)

Shape and observations of bloodstains


10

















20















30

















40

















50

















75

















100

















125

















150















200



















Questions:

  1. What is the independent variable in this blood drop experiment? On what axis must this variable be plotted on your graph?



  1. What is the dependent variable in this blood drop experiment?


  1. Is there a relationship between the height from which the blood is dropped and the size of the blood-spatter droplets? Support your answer with data from your graph.


  1. True or False: As the height from which the blood is dropped increases, the size of the blood spatter continues to increase. Again, support your answer with data from your graph.


  1. Blood is dropped from heights of 20 cm and 200 cm. Compare and contrast the outer edges of blood droplets produced from these two heights.



  1. Examine the blood spatter produced by dropping blood from the various heights. Is there a relationship between the height from which the blood is dropped and the number of satellites produced? Support your answer with data from your table.

  1. If someone accidentally dropped two or more drops of blood in the same location, what effect would it have on the blood-spatter pattern?





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