The number of gas molecules striking per second per square meter of the top surface of a table placed in a room at $20°\mathrm{C}$ and $1$ atmospheric pressure is of the order of ($k_{\mathrm{b}}=1.4\times {10}^{-23} \mathrm{J} {\mathrm{K}}^{-1}$ and the average mass of an air molecule is $5\times {10}^{-27} \mathrm{kg}$)