What are fluids?

The density of the atmosphere at sea level is $1.29 \; kg/m^3$. Assume that it does not change with altitude. Then how high (in $km$) would the atmosphere extend?

Three liquids of equal masses are taken in three identical cubical vessels $A$,$B$,and $C$. Their densities are $\rho_{A}$,$\rho_{B}$,and $\rho_{C}$ respectively,where $\rho_{A} < \rho_{B} < \rho_{C}$. The force exerted by the liquid on the base of the cubical vessel is

Why is the dam of a water reservoir thick at the bottom?

In a $U$-tube as shown in the figure,water and oil are in the left and right sides of the tube,respectively. The heights from the bottom for the water and oil columns are $15 \; cm$ and $20 \; cm$,respectively. The density of the oil is ...... $kg/m^3$. [Take $\rho_{\text{water}} = 1000 \; kg/m^3$]

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