Which of the following quantities is expressed as force per unit area?

Why is walking barefooted on a sharp gravel (grit) road difficult?

At a depth of $1000 \; m$ in an ocean:
$(a)$ What is the absolute pressure?
$(b)$ What is the gauge pressure?
$(c)$ Find the force acting on the window of area $20 \; cm \times 20 \; cm$ of a submarine at this depth,the interior of which is maintained at sea-level atmospheric pressure. (The density of sea water is $1.03 \times 10^3 \; kg \; m^{-3}$,$g = 10 \; m \; s^{-2}$.)

The volume of an air bubble is doubled as it rises from the bottom of a lake to its surface. The atmospheric pressure is $75 \, cm$ of mercury. The ratio of the density of mercury to that of lake water is $\frac{40}{3}$. The depth of the lake in metres is:

An open-ended $U$-tube of uniform cross-sectional area contains water (density $1.0 \text{ g/cm}^3$) standing initially $20 \text{ cm}$ from the bottom in each arm. An immiscible liquid of density $4.0 \text{ g/cm}^3$ is added to one arm until a layer $5 \text{ cm}$ high forms,as shown in the figure. What is the ratio $h_2/h_1$ of the heights of the liquid in the two arms?

$A$ $U$ tube with both ends open to the atmosphere is partially filled with water. Oil,which is immiscible with water,is poured into one side until it stands at a distance of $10\, mm$ above the water level on the other side. Meanwhile,the water rises by $65\, mm$ from its original level (see diagram). The density of the oil is ......... $kg/m^3$.