Temperature

temperature

Temperature theoretical definition Temperature: One has to be careful when defining temperature not to confuse it with heat. Heat is a form of energy. Temperature is something different. We could begin with a technical definition, but I would prefer to start with a question. How hot is it? The answer to this question (or a question like this) is a ...

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Flow Regimes

Flow Regimes

Flow Regimes Reynolds number Flow Regimes: The Reynolds number (Re) is the ratio of inertial resistance to viscous resistance for a flowing fluid. It is named after the British physicist and engineer Osborne Reynolds who is generally regarded as the first to realize its importance in 1883. Re = inertial resistance  = ρvℓ viscous resistance η where… Re = Reynolds number ρ = density of the fluid v = ...

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Aerodynamic Drag

Aerodynamic Drag

Aerodynamic Drag pressure drag Aerodynamic Drag: The force on an object that resists its motion through a fluid is called drag. When the fluid is a gas like air, it is called aerodynamic drag or air resistance. When the fluid is a liquid like water it is called hydrodynamic drag, but never “water resistance”. Fluids are characterized by their ability to flow. In somewhat technical language, a fluid is ...

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Viscosity

Viscosity

Viscosity Viscosity: Informally, viscosity is the quantity that describes a fluid’s resistance to flow. Fluids resist the relative motion of immersed objects through them as well as to the motion of layers with differing velocities within them. Formally, viscosity (represented by the symbol η “eta”) is the ratio of the shearing stress (F/A) to the velocity gradient (Δvx/Δz or dvx/dz) in a fluid. η = F̅/A Δvx/Δz or η = F/A dvx/dz ...

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Fluid Flow

Fluid Flow

Fluid Flow Fluid Flow: continuity equation For incompressible fluid flow… φ = V  = Av = constant  ⇒ A1v1 = A2v2 t If the fluid is compressible, then… I = m  = ρAv = constant  ⇒ ρ1A1v1 = ρ2A2v2 t Fluid Flow: Notes from The Economist — “A sverdrup (named for the Norwegian oceanographer and meteorologist Harald Sverdrup) the unit in which ocean currents are measured, is one million cubic metres of ...

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Buoyancy

Buoyancy

Buoyancy Buoyancy: Buoyant forces act on the foundations of buildings. Tokyo underground train stations need to be pinned down to avoid bobbing to the surface from the buoyant forces caused by increasing water levels. B = Fbottom − Ftop B = PbottomA − PtopA B = (ρfluidghbottom − ρfluidghtop)A B = ρfluidgΔhA = ρfluidgV = mfluidg B = Wfluid Archimedes’ principle: The buoyant force (B) on an object immersed in a fluid is equal to the weight of the fluid ...

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Pressure

Pressure Pressure is the ratio of force applied per area covered… P = F A The unit of pressur_e is the pascal ⎡ ⎣ Pa = N  = kg m/s2  = kg ⎤ ⎦ m2 m2 m s2 The pascal is also a unit of stress and the topics of pressure and stress are connected. Bed of nails (not really pressur_e but shear strain, which has ...

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Density

density

Density Density: Confusion of mass and density. Objects have mass. Materials have density. Density is the ratio of mass to volume for a material. ρ = m V Units 1,000 kg/m3 = 1,000 g/l = 1 g/cm3 Density of selected materials (~20 ℃, 1 atm) material density (kg/m3) material density (kg/m3) acetone 790 kerosene 810 acid, acetic (CH3COOH) 1,050 lard 919 acid, hydrochloric (HCl) ???? lead 11,350 acid, sulfuric (H2SO4) ...

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Resonance

Resonance

Resonance: Radio transmitters (including television transmitters, satellite uplinks, and cellular phones) broadcast at or near a particular frequency. We are swimming in a sea of different radio frequencies from both natural and artificial sources. How does your radio (television, satellite dish, or cellular phone) select the correct frequency from among all the others for decoding? This needs to be paraphrased. ...

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