## College Physics (4th Edition)

(a) $F = 1.0\times 10^5~N$ (b) $F = 2.25\times 10^4~lb$ (c) This huge force does not crush the desk because air pressure is not just a downward force. There is no pressure difference between the top of the desk, the bottom of the desk, the sides of the desk, or the air within the desk.
(a) We can find the downward force exerted on the desktop: $F = P~A = (1.0\times 10^5~N/m^2)(1.0~m^2) = 1.0\times 10^5~N$ (b) We can convert this force to units of pounds: $F = (1.0\times 10^5~N) \times \frac{0.225~lb}{1~N} = 2.25\times 10^4~lb$ (c) This huge force does not crush the desk because air pressure is not just a downward force. There is no pressure difference between the top of the desk, the bottom of the desk, the sides of the desk, or the air within the desk.