Explain why
(a) The blood pressure in humans is greater at the feet than at the brain
(b) Atmospheric pressure at a height of about 6 km decreases to nearly half of
its value at the sea level, though the height of the atmosphere is more than
100 km
(c) Hydrostatic pressure is a scalar quantity even though pressure is force
divided by area.
Explanations
(a) The blood pressure in humans is greater at the feet than at the brain
This is due to the effect of hydrostatic pressure in a fluid. The pressure increases with depth due to the weight of the fluid above. In the human body, blood behaves as a fluid in vertical columns. Since the feet are farther below the heart compared to the brain, the blood pressure is greater at the feet.
(b) Atmospheric pressure at a height of about 6 km decreases to nearly half of its value at sea level, though the height of the atmosphere is more than 100 km
Atmospheric pressure is caused by the weight of the air above a given point. The density of air decreases with height due to gravity and the compressibility of gases. Most of the atmospheric mass is concentrated closer to the Earth’s surface, so pressure decreases rapidly at lower altitudes. At 6 km, the air density and weight above are significantly reduced, leading to a pressure drop to about half of sea level pressure.
(c) Hydrostatic pressure is a scalar quantity even though pressure is force divided by area
Pressure at a point in a fluid acts equally in all directions and does not have a specific direction of application. While force is a vector, pressure is defined as a scalar because it describes the magnitude of the normal force per unit area, irrespective of direction. This isotropic nature makes it a scalar quantity.
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