4. Dripping Blood Blood drop grows until Wt (G) > S.T. Single drop breaks free (teardrop shape) Surface tension pulls in vertically Shape settles into sphere (0.05 ml) Does not break up until impact And horizontally Blood trickles downwards 4
5. Drop size . Standard drop size 50ul (0.05ml) . Rapid bleeding gives slightly larger drop Shaking/movement casts off smaller drops . 5
8. Free Falling Blood Droplets 8 . 50 ul 4.6 mm 7.5 m/s 4.2 to 5.4 m 0.5 ul 2.12 mm 2.4 to 3 m . 4.6 m/s 0.12 ul 1.32 mm 0.84 to 1 m . 3.3 m/s 0.06 ul 1.1 mm 0.5 to 0.65 m . 2.2 m/s
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10. Height Fallen Single drops of blood falling from fingertip onto smooth cardboard from various heights. No change in diameter beyond 7 ft. Adapted from Introduction to Forensic Sciences , W. Eckert, CRC, 1997 10
11. Effect of Target Surface . . Spreads out smoothly ST of spreading edge is broken by irregular surface 11 . . . .
12. Experiments with Falling Blood Droplets Terazzo floor whiteboard rough paper towel paper Fabric (theatre green) Height Target Surface 12 blood dropper ruler
13. Height/Surface Single drop of blood falling from various heights (m) onto various surfaces smooth floor paper towel fabric 13 0.5 1 2 3 0.5 1 2 3
14. Angle of Impact Adapted from Introduction to Forensic Sciences , W. Eckert, CRC, 1997 Gravitational dense zone at lower edge 14 90 10 70 20 30 60 50 40 80
15. Wave Cast-off David Sadler: 15 . Parent drop wave cast-off Tail of wave cast-off points back to parent drop Tail of elongated stain points in direction of travel
18. Point of Origin length width Angle of impact = arc sin W/L 18 1 Distance from point of convergence Height above point of convergence Origin 85 60 45 30
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21. Herbert Leon MacDonell, Laboratory of Forensic Science, P.O. Box 1111, Corning, New York, 14830, USA 21
30. Cast off Pattern (2/2) ? Sequence 1 (4 spots) 2 (3 spots) 3 (2 spots) If weapon does not pick up more blood, spatter from subsequent backswings becomes progressively less. In practice weapon picks up more blood with each successful blow. 30
55. Medium velocity blood spatter. Point of impact 15 cm in front of vertical target surface 6” ruler 55
56. Flick 1: Blood flicked between middle finger & thumb onto a vertical smooth surface from a distance of 15 cm 56
57. Flick 2: Blood flicked between middle finger & thumb onto a vertical smooth surface from a distance of 15 cm 57
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59. Gunshot: back& forward spatter Bloodstained foam held just above target surface. Back-spatter on entry Forward spatter on exit Bullet passing L to R just above sheet 59 bullet Bullet enters foam bullet exits foam