Physics 121 11/22/10 Prof. E. F. Redish 1 11/22/10 1 Physics 121 11/22/10 2 Physics 121 11/22/10 3 Physics 121 F A The force takes its direction from A. FpFpAA==Pressure has no direction! It acts in all directions at once!Physics 121 11/22/10 Prof. E. F. Redish 2 11/22/10 5 Physics 121 11/22/10 7 Physics 121 F = p0 A (could be outside air pressure or due to external weights) A fluid of uniform density p0A pA W = mg 11/22/10 8 Physics 121 gdpppAApAdgpAApVgpAApmgFFupdown+==+=+=+=0000A d * We assumed uniform density. Is this OK? For water ( ~ 1000 kg/m3) yes. For air ( ~ 1 kg/m3) OK for meters — not km.Physics 121 11/22/10 Prof. E. F. Redish 3 11/22/10 9 Physics 121 d1 d2 p1 p2 11/22/10 10 Physics 121 d1 d2 p1 p2 mgVgAddgFAgdpgdpFAppFgdppgdppApApFnetnetnetnet===+==+=+==)()()(1210201220210112The buoyant (upward) force = the weight of the fluid displaced. 11/22/10 11 Physics 121Physics 121 11/22/10 Prof. E. F. Redish 4 11/22/10 13 Physics 121 11/22/10 14 Physics
View Full Document