The Nature of Liquids
Did you ever wonder why they can take your blood pressure by measuring it on your arm or your leg? Blood pressure is the pressure the heart puts on your blood, so how can they measure it on your arm? The answer to this question is rooted in the nature of liquids and a famous law of physics called Pascal's law. This law says "pressure exerted on a fluid is distributed throughout the fluid." What that means is that when the heart puts pressure on your blood, that pressure is the same everywhere in your body (if you're laying down). This is also the reason why when you put pressure on the brake pedal in your car, the pressure is distributed to the wheels, a long way from where your foot is.
All of this would not work well however, if blood was like air. When you put pressure on air it compresses and becomes more dense. This is why air rushes out of your tire when you get a hole in the tire or out of a balloon when it bursts. The molecular structure of liquids is such that they compress very little. When your heart pressurizes your blood, that pressure is the same instantly everywhere in your body. Your brain does not have to wait to get blood, and the blood comes smoothly bathing cells in the vital soup of oxygen and nutrients that keeps them healthy.
Psalm 139:14 says "I will praise the Lord, for I am fearfully and wonderfully made." Not only are we made fearfully and wonderfully, but the materials that make up our bodies have carefully designed characteristics which make them ideal for the uses they serve in our bodies.
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