BLOOD SPATTER

COHESIONA 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 SPATTERPASSIVE 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)

• IF OPPOSITE = 1.5 cm and HYPOTENUSE = 3.0 cm …– Calculate angle above

• OPPOSITE / HYPOTENUSE = WIDTH / HEIGHTH– THEREFORE …

Distance A-B is OPPOSITEDistance B-C is HYPOTENUSE

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