Fluid StaticsFluid Statics

Why do your ears hurt when Why do your ears hurt when you dive deep into a pool, and you dive deep into a pool, and how can steel float on water?how can steel float on water?

Fluid statics: pressure Fluid statics: pressure and densityand density

Pressure is Force/Area (N/mPressure is Force/Area (N/m22 = Pascals) = Pascals) A thumb tack is a good way to feel the A thumb tack is a good way to feel the

difference between Force and pressure.difference between Force and pressure. The atmosphere has a constant nominal The atmosphere has a constant nominal

pressure of 1.01 x 10pressure of 1.01 x 1055 Pa (or 1 atm) Pa (or 1 atm)

Fluid Statics: Pressure Fluid Statics: Pressure and Densityand Density

Density Density ρρ = mass/volume = mass/volume ρρ(water) = 1000 kg/m(water) = 1000 kg/m33

ρρ(aluminum) = 2700 kg/m(aluminum) = 2700 kg/m33

ρρ(gold) = 19300 kg/m(gold) = 19300 kg/m33

Fluid Statics: change in Fluid Statics: change in pressure with increased pressure with increased depthdepth

The deeper you dive into a pool the greater the The deeper you dive into a pool the greater the pressure is.pressure is.

Increased pressure PIncreased pressure Pgauge gauge = = ρρgh = pressure gh = pressure due to the weight of the fluid at a given depth due to the weight of the fluid at a given depth h.h.

The gauge pressure is the amount of increase The gauge pressure is the amount of increase in pressure compared to the surface (typically in pressure compared to the surface (typically the surface pressure is atmosphere)the surface pressure is atmosphere)

Hydrostatic pressure

Pressure in a fluid PPgauge gauge = = ρρghgh P=Pgauge + Psurface P=Pgauge + Psurface ( Psurface= Patm)( Psurface= Patm)

Fluid Pressure increase Fluid Pressure increase with depthwith depth

The total pressure at a given depth is The total pressure at a given depth is P=Pgauge + Psurface (where Psurface P=Pgauge + Psurface (where Psurface usually means Patm)usually means Patm)

Fluid pressure depends on depth and not Fluid pressure depends on depth and not on the shape of the container. on the shape of the container.

Buoyant Forces and Buoyant Forces and Archimedes Principle (280 Archimedes Principle (280 B.C. Greek scientist)B.C. Greek scientist)

The buoyant Force pushing up by a fluid The buoyant Force pushing up by a fluid = weight of the fluid displaced= weight of the fluid displaced

To calculate the weight of the fluid To calculate the weight of the fluid multiply the fluid density (multiply the fluid density (ρρ) by the ) by the displaced Volume and by gdisplaced Volume and by g

FFbuoyantbuoyant = = ρρVg = weight of the fluidVg = weight of the fluid

Archimedes principleArchimedes principle

Buoyant forceBuoyant force