Blood Drop Lab Blood spatter from a sneeze

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

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

Blood Drop

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…. Which one is most “eccentric? ”

Measuring the shape of the blood drops

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

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

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 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)