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solving crimes with physics
Blood pressure is a factor in the amount of blood a person loses
when they are cut deeply. Blood pressure is controlled by two main
factors: the individual’s heart and the muscles of the major blood
vessels.
Arteries, being muscular tubes, can contract and reduce the
amount of space within themselves in response to instructions from
the brain. Under stressful conditions, the blood vessels contract to
force an increase in the rate of blood flow, which in turn increases
the rate of oxygen transfer to the cells. When a person is fright-
ened, the need for additional oxygen to the cells is obvious. More
oxygen means the person is better able to flee or fight.
has some small clots in it because blood tends to begin clotting as soon as
a person is cut.
Forensic experts usually call blood that falls straight to the ground from
a victim passive blood loss. Drips and oozing are passive because there is
no energy from the body moving them out away from the source. Passive
blood sometimes drips off in one location, each drop falling on top of the
last, or in a trail as the wounded person moves.
When a major blood vessel is damaged, blood often sprays out strongly.
Blood that sprays out in large amounts is called gushing or spurting blood.
Gushing blood is the main source of what forensic scientists call projected
blood, which means that energy forced the blood out of a person’s body.
Projected blood can spray for a long distance because of blood pressure.
In addition, because of the high pressure, a gush of blood can contain
