Adapted from BIOFAX! Flinn Scientific FB1643
Blood Spatter Analysis Lab
Introduction:
Blood and bloodstains are common at many crime scenes. In addition to the
blood type, the stain patterns can often reveal key elements in reconstructing the
crime. In this lab, simulated blood will be used to collect data on blood stain
patterns.
Background:
It is important that a crime scene investigator examines the location,
distribution, and appearance of blood stains and spatters to interpret and
reconstruct a crime. The actual analysis at the crime scene can become very
complex and usually requires three-dimensional thinking and sophisticated
measuring techniques.
Blood is slightly denser and 3-4 times more viscous than water. It is made up
of three components that are held loosely in a suspension. A cohesive force referred
to as surface tension holds the liquid contained in a drop of blood together. This
force tends to keep a drop of blood in a spherical shaped as it falls. When a drop of
blood is released and is free to fall under the influence of gravity, the same physics
principals govern it as any free-falling object.
In an actual crime scene analysis, the most important variable to consider
and try to control is the contact surface. Blood will leave a different pattern
depending on the type and nature of the contact surface. The harder and less
porous the surface, the less the blood drop will break apart and the softer more
porous the surface is, the more the droplet will break apart.
Adapted from BIOFAX! Flinn Scientific FB1643
Name:
Class Period:
Date:
Blood Spatter Analysis Lab
Objective: Use simulated blood to produce blood spatter at different heights. We
will describe the blood spatter in relation to the distance it was dropped,
acceleration, force, and energy.
Materials:
Safety Precautions:
1. Wear goggles and protective clothing, SIMULATED BLOOD WILL STAIN.
2. Use newspapers or paper towels to protect your work area.
3. Clean up spills immediately and wash hands with soap if necessary.
Draw Laboratory set-up:
Adapted from BIOFAX! Flinn Scientific FB1643
Pre-Lab:
1. Define VISCOUS:
2. Define SUSPENSION (AS RELATED TO A LIQUID):
3. Define SURFACE TENSION:
4. What are the four main components of blood?
Part A. Free Fall Data
Adapted from BIOFAX! Flinn Scientific FB1643
Graph:
Post-Lab:
1. Graph results USING MICROSOFT EXCEL. Do not forget appropriate title, axis
label, and unit.
2. What is the independent variable? Dependant variable?
3. Describe the changes to the diameter of the spattered drops as the height
was increased? EXPLAIN YOUR ANSWER IN TERMS OF :
a. Acceleration
b. Force
c. Energy
4. Describe any other patterns in the spattered drops in addition to the
diameter changes that might help in indentifying the height of an unknown
drop.
5. What do you think the diameter of blood spatter would be at 200cm? Explain
your reasoning.