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solving crimes with physics
Each person has thousands of miles of blood vessels in her body.
The total length of all the veins, arteries, arterioles, and capillaries
in one adult human body is estimated to be long enough to wrap
around the planet at the equator . . . twice! Imagine packing all
those miles of blood vessels into a human body. No wonder people
bleed no matter where they’re cut.
striking different surfaces. One nice thing is that most people have blood of
exactly the same composition. A key aspect of blood chemistry is that hu-
man blood always has about the same
viscosity
—it is nearly always about
the same consistency. Blood, being a relatively viscous fluid, does not flow
quickly when compared to water, which is a nonviscous liquid.
The chemical composition of blood gives it a large amount of surface
tension—the molecules that make up blood are attracted to one another, so
they tend to stick to each other. This is why blood behaves as it does when
it runs down a surface; the high surface tension keeps the blood in droplets
even as it moves down a surface. Liquids with low surface tension tend to
break up as they fall down a surface.
The Biology of Blood Flow
Blood is kept within the circulatory system under extreme pressure. A cut to
a major blood vessel can result in a gush of blood spraying more than ten
feet (3 meters) from the body.
