BLOOD SPATTER
COHESION
A KEY PROPERTY OF BLOOD
• Blood is a water based substance, creates
property of blood known as cohesion
– Cohesion – molecules of the same substance
attracting one another
• Surface Tension- molecules do not want to separate
from one another
FACTOR EFFECTING SIZE OF SPATTER
PASSIVE DROP
• PASSIVE DROP – DROP THAT FALLS ON ITS
OWN DUE TO ONLY GRAVITATIONAL FORCES
– INITIAL SIZE OF DROP
• Bigger drop = Bigger SPATTER
– HEIGHT / VELOCITY OF DROP
Effect of Height/Velocity of Pattern of
Blood Spatter
• Increase VELOCITY = Increase in DIAMETER of
SPATTER in PASSIVE drops of blood
– Passive drop increases velocity as it falls due to effects
of gravity.
– Spatter will not become larger at heights above 7 feet
• Droplet reaches TERMINAL VELOCITY due to friction
– Terminal velocity – maximum velocity
• Increase VELOCITY also creates
– Increased SPIKES
– Increased SATELITES
4 PHASES OF IMPACT
• CONTACT AND COLLAPSE
– Blood droplet flattens on impact
• DISPLACEMENT
– Blood droplet spreads out
• DISPERSION
– Some particles fly off main drop at edges
• RETRACTION
– Particles not completely separated suck back into
main drop due to adhesive forces
SATELLITES AND SPIKES
• Satellite droplets—drops that have been separated from
main droplet
– When blood falls from a height, or at a high velocity,
– It overcomes its natural cohesiveness, and
– Separates from the main droplet
• Spiking patterns—drops that don’t make it completely away
form main drop
– Cohesion causes particles not completely separated to retract back
into main drop
– Form around the droplet
edges
Spikes and Satellites
• Use terms collapse, displacement, dispersion,
and retraction to describe how satellites and
spikes seen below have formed.
DIRECTION OF BLOOD
EFFECT OF ANGLE ON SPATTER
CALCULATING ANGLE using TRIGONOMETRY
• ANGLE = INVERSE SIN (OPPOSITE/HYPOTENUSE)
Distance A-B is OPPOSITE
Distance B-C is HYPOTENUSE
• IF OPPOSITE = 1.5 cm and HYPOTENUSE = 3.0 cm …
– Calculate angle above
• OPPOSITE / HYPOTENUSE = WIDTH / HEIGHTH
– THEREFORE …
CALCULATING ANGLE USING
TRIGONOMETRY
• THEREFORE ANGLE = INVERSE SIN (WIDTH /
LENGTH)
Lines of Convergence
• Lines of convergence—two or blood splatters
can pinpoint the location of the blood source
– Circled area shows where lines converge = source