1!Phys 2101 Gabriela González 2!Density: mass per unit volume ρ = Δm/ΔV. If uniform, ρ = m/V SI units: kg/m32!3!Pressure: force per unit area p = F/A SI units: N/m2 = Pa Non-SI units: 1 atm = 1.01x105 Pa = 760 torr =760 mm Hg 1 atm = 14.7 lb/in2 (psi) 4!Pressure: force per unit area p = F/A SI units: Pa = N/m2 = (kg m/s2)/m2 = kg/(ms2) Non-SI units: 1 atm = 1.01x105 Pa 1.01 hPa = 760 torr =760 mm Hg = 29.9 in Hg 1 atm = 14.7 lb/in2 (psi)3!5!Pressure in fluids at rest increase with depth, due to weight of fluid on top: F = F0 + mg = F0 + (m/V)gV = F0 + ρghA p = F/A = p0 + ρgh Pressure decreases when climbing mountains, and increases when diving: In both cases, be careful with pressure changes! A=area h 6!• How deep in the sea is the pressure twice as much the pressure at the surface? • Would the answer be different in a mountain lake?4!7!How long should a mercury barometer be to measure 29 psi tire pressure? http://auto.howstuffworks.com/pressure-gauge.htm 8!A change in the pressure applied to an enclosed incompressible fluid is transmitted undiminished to every portion of the fluid and to the walls of its container.!Hydraulic lever: Fi/Ai=F0/A0 F0=Fi (A0/Ai) A force amplifier!5!9!http://auto.howstuffworks.com/auto-parts/brakes/brake-types/brake3.htm 10!When a body is submerged in a fluid, a “buoyant” force Fb from the surrounding fluid acts on the body, directed upward and with a magnitude equal to the weight of the fluid that has been displaced by the body.6!11!What does a balance read when it is measuring the weight of a submerged body? mg N mg N Fb Use a block of (real) gold to balance the crown in a lever: we then know the weight of the crown is the same as the gold block. If the crown is made out of gold, the crown and the block will also have the same volume, and produce the same buoyant force when the lever is submerged, so the equilibrium should still hold. If it doesn’t, we know the crown is not made out of gold. 12!In the figure shown, is the crown made out of a more or less dense