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30 Cards in this Set
- Front
- Back
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forces from solids and fluids
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solids can withstand forces from all directions
fluids are constantly breaking and reforming bonds bc high KE, so only temporal resistance to forces EXCEPT can withstand forces NORMAL (perpendicular) to its surface - bc of pressure |
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intensive properties analogous to mass and Energy
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density and pressure
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Density
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p=m/V "heaviness"
assume all liquids and solids are totally incompressable and therefore have constant density related to specific gravity: denisty of substance/density of water |
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specific gravity
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density of substance/ density of water
less than one indicates substance lighter than water density of water= 1000kg/m3 1 gm/cm3 |
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density of water
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1000kg/m3
1gm/cm3 |
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fluid pressure
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average magnitude of the force of fluid molecs hitting a submerged object / by area over which collisions are taking place (surface area)
P=F/A Pascals pressure experienced by object also magnitude of change in momentum/ time duration of collisions and area also measure of kinetic energy due to random velocities of molecs distributed over the fluid volume |
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fluid at rest
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only experiences forces perpendicular to its surface
P=density x g x y (depth) independent of area!! total P = summed pressure due to each fluid if in layers ** must add air if open container! Patm=101,000 Pa |
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gauge pressure
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pressure compared to local atmospheric pressure
atm P is arbitrarily given value of 0, therefore anything below is negative P |
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Pascal's principle
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pressure applied anywhere to an enclosed incompressible fluid will be distributed undiminished throught that fluid
** doesnt apply to gas b/c compressible |
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absolute pressure
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pressure measured relative to vaccum
gauge pressure plus atmospheric pressure |
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hydraulic lift
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works via pascals principle
piston 1 has smaller area, connected to piston 2 via tube less force needed to push on 1 to move 2, but proportionately less distance moved (because work doesn't change, only lowers force needed in ideal machine) |
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buoyant force
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upward force acting on a submerged object
is equal to the weight of the fluid displaced by the submerged object Fb=desity of fluid x V x g if submerged, displaces fluid equal to its VOLUME! if floating, displaces fluid equal to its WEIGHT! BUT wont be fully submerged (% submerged = density object/density liquid) |
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fraction sumberged of floating object
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density of object/ density of liquid it is in
*** will displace an amount of fluid equal to its own WEIGHT (fully submerged will be equal to its volume) |
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centre of buoyancy
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where centre of mass would be if object was uniformly dense
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types of motion a moving fluid can have
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random translational motion - contributes to fluid P like fluid at rest
uniform translational motion - shared by all molecs equally at a given location (motion of fluid as a whole) * doesnt contribute to pressure! |
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ideal fluids differ from real fluids...
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1. no viscosity
2. incompressible (uniform density) 3. lacks turbulence (steady flow, same velocity thru pt) 4. irrotational flow |
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viscosity
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measure of fluid's temporal resistance to forces not perpendicular to its surface - tendency to resist flow
similar to drag - created by viscosity and pressure due to motion |
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drag
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created by viscosity and pressure due to motion
always opposes motion of an object through a fluid |
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continuity equation
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Q = Av
Q rate at which volume passes through pipe (volume flow rate) in ideal fluid, flow rate is constant NOT in real fluid - depends on pipe length and radius narrower pipe, greater velocity |
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Bernoulli's equation
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MUST MEMORIZE
P + pgh + 1/2pv2 = K K is constant specific to a fluid in a given situation of flow ** h is distance above a point as velocity increases, pressure decreases** - think running from bees... uniform trans E is achieved by borrowing E from random translational E... |
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Non-ideal fluids
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- drag and viscosity act to impede flow - as move away from fluid-object interface, decrease effect
(therefore if narrow pipe, velocity will still increase, but not as much as ideal b/c drag has increased too) |
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surface tension
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intensity of intermolecular forces per unit length
intermolecular forces pull inwards, min surface area, creates sepherical shape dependent on temperature (weaker with high temp) and fluid with which it is interfacing with |
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capillary action
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fluid is pulled up thin tube
due to intermolecular forces of surface tension = cohesive and forces between molecs of tube and fluid = adhesive if cohesive stronger, will get convex meniscus (fluid pulled down by strong vertical comp surface tension) if adhesive forces stronger, get concave miniscus, fluid pulled up by vert comp of surface tension |
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stress
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force applied to an object/ area over which force is applied
N/m2 |
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strain
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fractional change in object's shape
ratio of change in dimension compared to original dimension no units * how object responds to stress |
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modulus of elasticity
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stress/strain
up to some max stress, modulus of elasticity is a constant for a specific substance (find max from exp) yield point - doesnt reform fracture point - breaks |
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Young's modulus
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tensile stress (E)
stress(F/A)/ strain (change height/height) |
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Shear modulus
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shear stress
stress (F/A)/ strain (change x/ height) |
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bulk modulus
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compression and expansion (B)
stress (change in P)/ strain (change in volume/original volume) |
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thermal expansion
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solids typically expand when heated
linear (one dimensional) or volume (3D) change in L = L alpha change in T change in V = V beta change in T alpha and beta are constant to particular substance |
