Liquid Flashcards
Inertial effects
moving the fluid away from where we want to be
viscous effect
overcoming the friction btw the fluid layers that are moving with us and those that are not
Reciprocal motion
“ABCBABCBA”, when the shape changed back to its original configuration with the exact reversed sequence –> the body moved back to its initial position.
NOT “ABCDABCDA”
- moving oar left and then right)
Net displacement
only occur in non-reciprocal motion.
more than one DOF is necessary to create non-reciprocal motion. (rotation around helical axis)
Newtonian fluids
- purely viscous fluids
- when the viscous stress is linear to the rate of strain
Non-newtonian fluids
- Viscous stress is non-linear of the rate of strain
- Viscosity change faster than the rate of shear
- > “vätskor tjocknar vid omrörning (stärkelse blandat med vatten)”
- > “vätskor förtunnas (ketchup eller målarfärg)”
Strain rate
change in strain(deformation) of a material with respect to time§
Non-newtonian fluids - viscoelastic and inelastic (purely viscous non-newtonian fluid
Viscoelastic
- time-dependent
- shear rate and shear strain is related to shear stress
- both viscous and elastic characteristics when undergoing deformation.
- ex. isolating vibration, dampening noise, absorbing shock…
- This differ from elastic: viscoelastic has a visc. factor –> strain rate dependent on time. Purely elastic material -> do not dissipate (slösa bort) energy (heat), while a viscoel. does.
Inelastic
- time-dependent
- shear strain is unique non-linear of shear stress
shear rate
shear strain
shear stress
- rate of change of velocity at which one layer of fluid passes over an adjacent layer (du/dy)
- the length of deformation divided by the perpendicular length in the plane of the force applied (x(t)/y)
- stress parallel to the cross section of the material (tau)
Brownian motion/random walk
Tracking of how (many) small particle moves in a fluid
- depends on viscosity, probe size and temperature
- the smaller particle the larger diffusion constant
Microscopic diffusion
- This is a example of brownian motion
- ex. air molecules
Macroscopic diffusion: Fick’s law
” With an enormous number of solute molecules, randomness becomes undetectable: The solute appears to move smoothly and systematically from high-concentration areas to low-concentration areas. This smooth flow is described by Fick’s laws. “
- No. of atom crossing area A per unit time.
Biased random walk
- random walk that is biased in one direction –> net drift on average of particles in one specific direction
Ex. higher probability of moving right than left. Or when it moves right, it moves twice as much as to the left.
biased random walk: Chemotaxis
- direct their movement according to certain chemicals in their environment
Ex. bacteria swimming toward highest conc. of food molecules
biased random walk: Thermophoresis
different particles types exhibit different responses to the force of a temperature gradient.
- higher temp (a particle experiences a force) -> smaller particle net movement
