First of the Day….

Blood spatter from a sneeze from a bloody nose Blood Spatter Lab Blood spatter from a sneeze from a bloody nose

“Remember… it’s blood ‘Spatter’ not blood SpLatter.”

Blood Drop blood spatter animations

Eccentricity: of an ellipse is the ratio of the distance between the foci to the length of the major axis; this is necessarily between 0 and 1. If the ellipse has the Cartesian equation

Basically “eccentricity” is how “oval” and ellipse is… Basically “eccentricity” is how “oval” and ellipse is…. Which one is most “eccentric?”

Measuring the shape of the blood drops

Impact angle = sin-1(arcsin) width (d) length (D)

Impact angle = sin-1 (arcsin) width length drop on left: W = 1.8 cm L = 2.8 cm Impact angle = sin-1 (arcsin) width length = sin-1 (arcsin) 1.8 cm 2.8 cm = sin-1 (arcsin) (0.643) = 40 degrees Do first 0.64285714….

0.64285714….

drop on right: W = 1.2 cm L = 5.23 cm Impact angle = sin-1 (arcsin) width length = sin-1 (arcsin) 1.2 cm 5.23 cm = sin-1 (arcsin) (0.229) = 13 degrees

Formula for Table 1 Angle of Impact Lab Impact angle = sin-1(arcsin) width length ¼” = one foot on diagram on your answer sheet Formula for Table 2 Height above point of target XY = tan(i) x XJ, angle i being the angle of impact from the previous data table

Blood Spatter Alteration of bloodstain over time Blood dries and clots over time. Difficult to estimate the time the blood exited the body. Clotted smears can indicate time of movement

Blood Spatter Determining Direction of Blood The angle can be determined mathematically. Width/Length, then take the inverse sin (sin-1). This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle)