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Published byJack Preston Modified over 9 years ago
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2009©Forensic Science Today Blood Stain Pattern Analysis
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2009©Forensic Science Today A Little Science All fluids follow the laws of physics –What Forces affect falling objects? –Newton’s Laws of Motion???
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2009©Forensic Science Today Falling Gravity Air Resistance Surface Tension, in the case of any fluid containing a high % of H 2 O Gravity pulling down Molecules attracted to one another causing spherical shape Falling Blood Drop Air drag
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2009©Forensic Science Today What Did Newton Tell US? Resists changing motion until a force is applied (1 st Law) –blood tries to remain moving at the speed of the source –As gravity pulls it down, it is shaped By air and surface tension
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2009©Forensic Science Today Newton’s 2 nd Law Force applied is proportional to Acceleration achieved F = mass x acceleration Work done = F x distance fallen –Greater fall results in greater spattering
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2009©Forensic Science Today Wider spot from greater fall Greater work - Weakens surface tension
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2009©Forensic Science Today Greater work done Flatter stain from reducing surface tension
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2009©Forensic Science Today Newton’s 3rd Law Action and Reaction –Force of impact causes floor to apply reaction force on blood Floor
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2009©Forensic Science Today Tell Us…. Information about –Direction of movement –S peed of movement –Point of origin –Distance fallen and –Angle of impact (as well as other information)
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2009©Forensic Science Today Direction of Movement Shaped by –Resists leaving the source –Air resistance –Surface tension and –Impact Tail shows direction
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2009©Forensic Science Today Speed of Movement Stain is more elongated with faster movement Slower movement Faster movement
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2009©Forensic Science Today Low Velocity Stain
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2009©Forensic Science Today Medium Velocity Stain
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2009©Forensic Science Today High Velocity Stain
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2009©Forensic Science Today Examples of Angle of Impact
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2009©Forensic Science Today Point of Origin Draw lines down center of long axis of stains All arrows intersect at origin
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2009©Forensic Science Today Distance Fallen Greater fall –Wider, flatter stain
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2009©Forensic Science Today Angle of Impact Calculate with two measurements Length of stain and width of stain Impact Angle θ = sin -1 (length/width) L W
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2009©Forensic Science Today Other patterns Other patterns that can reveal information The most common and the least controversial More Research needed
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