Question

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

Answer 1

(a) The height of the blood column in the human body is more at feet than at the brain. That is why, the blood exerts more pressure at the feet than at the brain.

(Pressure $=\rho gh$)

where $h=$ height, $\rho$ = density of liquid and $g=$ accleration due to gravity)

(b) Density of air decreases very rapidly with increase in height and reduces to nearly half its value at the sea level at a height of about 6 km. After 6 km, the density of air decreases but rather very slowly.

(c) When force is applied on a liquid, then according to Pascal's Law, the pressure in the liquid is transmitted in all directions.

Hence, hydrostatic pressure does not have a fixed direction and it is a scalar physical quantity.