Fluids

• what are the three categories of flows?

  fluids, dilute (fluid dominated) and dense (particle dominated)
• what is a fluid?

  anything that can flow and is unable to hold its shape
• are gases fluids?

  yes
• in environmental studies, what do we consider all liquids?

  incompressible
• what governs fluid motion?

  fluid mechanics
• what laws do we consider when looking at fluid motion?

  newtons three laws of motions and the three laws of conservation
• what is newtons first law of motion?

  if there is no force applied to an object, it remains at rest or moves at a constant speed
• what is newtons second law of motion?

  if there is a force applied on the fluid, this force will create an acceleration
• what is the equation that links into newtons second law of motion?

  force = mass x acceleration
• what is newtons third law of motion?

  whenever there is an action, there is a reaction - when a force is applied to an object, the object gives the same force back in a different direction
• what is the law of conservation of mass?

  in a closed system, if there is no mass added or removed, then the mass of the whole system will remain constant. mass cannot be created or destroyed
• what can not be done to mass?

  create or destroy it
• what is the law of conservation of momentum?

  momentum cannot be created or destroyed, only changed when there is a force applied to the system
• what is the equation which goes with the law of conservation of momentum?

  momentum = mass x velocity
• what is the law of conservation of energy?

  energy within a system cannot be created or destroyed, however it can be converted
• what does delta mean?

  change
• what is viscosity?

  the resistance to the force applied or the resistance to the deformation that follows when force is applied
• what is the cause of viscosity?

  the internal friction between the molecules
• how can we quantify viscosity?

  by looking at the difference in how much the layers have dragged above or below those which have been deformed by stress
• how is stress defined?

  forced divided by area
• along with stress, what is also defined as stress divided by area?

  pressure
• what is the difference between stress and pressure?

  pressure is working on the surface, whereas stress is working parallel or perpendicular to the surface, dragging other layers to flow with it
• what is the relationship between shear stress and resulting strain?

  directionally proportional
• what is dynamic viscosity?

  applied stress divided by the rate of resulting strain
• what is kinetic viscosity?

  dynamic viscosity divided by fluid density
• what is viscosity a function of?

  temperature
• what is the relationship between temperature and viscosity?

  the higher the temperature, the lower the viscosity
• what does viscosity determine?

  how fast fluids move, how they mix, how well they transport material and the forces they apply on objects as they pass through
• what is the fundamental distinction in fluid motion?

  laminar vs turbulent flow
• what determines the distinction between laminar and turbulent flow?

  viscosity
• what can be used to predict whether a flow is laminar or turbulent?

  Reynolds number
• what does a high Reynolds number suggest?

  a turbulent flow
• what does a low Reynolds number suggest?

  a laminar flow
• what Reynolds number sees the transition from laminar to turbulent flow?

  500 to 3000
• what is the flow of a fluid with a Reynolds number below 500?

  laminar
• what is the flow of a fluid with a Reynolds number above 3000?

  turbulent
• what causes turbulence in laminar flows?

  molecule to molecule interactions
• what causes tuburlence in turbulent flows?

  turbulent eddies - spinning or swirling fluid structures
• what must cancel out in two dimension flows?

  change of flow speed in direction x and change of flow speed in direction y
• what is acceleration?

  change in speed divided by the time the fluid takes to get across the box