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# THE MCAT-PHYSICS 5

### FLUIDS AND SOLIDS

Which have intermolecular bonds (s,l,g)? solids and liquids
WHat can withstand perpendicular forces? gases, liquids, solids
What can withstand parallel forces? solids
specific gravity (2) 1.) p = p(material) / p(water) at 4C 2.) Weight / buoyant force
Pascal's principle Pressure applied to enclosed fluid is transmitted equally throughout an incompressible fluid and walls of container
Pascal's Equation P1-P2 = p(y2-y1)g
Total Pressure Equation P(total) = P(atm) + pgh
When a fluid comes to rest, what forces does it experience? normal force and gravity
What are extensive properties? change with quantity of substance (mass and energy)
What are intensive properties? do not change with quantity of substance (density and pressure)
What are incompressible and have constant density? liquids and solids
Does a bucket or cup of water have a greater density? NEITHER -mass refers to inherent mass -liquids are incompressible
Why does density of gas change? gases are compressible --> change volume --> change density
2 densities of water p = 1000 kg/m^3 p = 1 gm / cm^3
What is fluid pressure? measure of the KE due to random velocities of molecules within a fluid distributed over fluid volume
Relate Patm and Pascals P(atm) = 101,000 Pa
Does Pascal's Principle apply to gases? NO --> gases are compressible
Does the shape of a container affect fluid pressure? NO --> fluid pressure is a function of depth -pressure everywhere at a given depth in same resting fluid is constant
Does an ideal machine ever change work? NO
2 equations for Hydraulic Lift? F1d1 = F2d2 F1/A1 = F2/A2
What does a sunken object displace? volume of fluid equal to its own volume
What does a floating object displace? volume of fluid equal to its own weight
When an object is sunk, what forces act on it? buoyant force and normal force
What does buoyant force equal to for a floating object? p(medium) * V(displaced) * g
What does weight equal to for a floating object? p(object) * V (object) * g
How are weight and buoyant force related for a floating object? W = B
How to calculate percent submerged for a floating object? Relative densities = percent submerged
V(object) > V (displaced) for what? floating object
What is apparent weight? Normal force
What does buoyant force equal to for a sunken object? p (medium) * V (object) *g
What does weight equal to for a sunken object p (object) * V (object) *g
How do weight and buoyant force relate to density for sunken object? weight / buoyant force = p(object) / p(medium)
Under what conditions of volume and density will an object float? V(object) > V (displaced) p(object) < p(medium
Under what conditions of weight, buoyant force, and density will an object sink? W > B p(object) > p(medium)
What IMF account for surface tension? H-bonds or Van der Waals
Water vs. ethanol: which will evaporate first / which will condense first? -ethanol -water
What happens with surface tension increases? SA decreases, volume stays the same, spherical shape, evaporate less
Cohesion attraction between same molecules
What is viscous force? -fluid flowing through pipe experiences forward and opposing frictional force -measure of fluids resistance to forces not perpendicular to surface
In a pipe, where is the fluid the fastest? Slowest? center near edges of pipe
Increase temperature of fluid, what happens to viscosity of liquid and gas? liquid viscosity decreases, gas viscosity increases
Flow Rate Volume of fluid that passes through a pipe per unit time --> different from flow speed of a fluid
Poiseuille's Principle Q = pi*r^4 / 8nL (P1-P2)
What does high BP mean in relation to Poiseuille's Principle? Heart is generating a large P1 to produce necessary Q to get blood to tissue
Continuity equation A1V1 = A2V2
Why does fluid flow? flows from region of high pressure to low pressure -->more precisely direction of fluid flow is fluid's tendency to find greatest entropy
What work is done on fluid? pressure difference pushing fluid in one direction W = deltaKE + deltaPE
Bernoulli's Equation P1 + 1/2pv^2 + pgy1 = P2 + 1/2pv^2 + pgy2 --> think conservation of energy!
What happens to pressure when there is higher velocity? Pressure decreases
How to increase turbulence? (density, avg velocity, radius) increase density, average velocity, and radius of vessel
Does buoyant force change with depth? NO --> due to difference in pressure only between upper and lower surfaces
What kind of motion can molecules in a moving fluid thought to have? 1.) random translational motion (contributes to fluid pressure for fluid at rest) 2.) uniform translational motion (does not contribute to fluid pressure)
Ideal Fluid (4 characteristics) 1.) No viscosity 2. ) incompressible --> uniform density 3.) no turbulence 4.) irrotational flow
What is turbulence? at any point in fluid, velocity may vary with time
Why does pressure decrease when velocity increases? uniform translational KE is achieved by borrowing energy from random translational KE --> pressure goes down
What happens to pressure when you increase cross-sectional area? increases
What happens to pressure when you decrease cross-sectional area? decreases
What creates drag? narrow and long pipe
Does narrowing a pipe increase velocity for ideal and non-ideal fluid? YES --> less effect on non-ideal because of drag
Why does pressure decrease when cross-SA decreases? A1V1 = A2V2 -faster velocity --> less opportunity to interact with walls of vessel -lower pressure
What does surface tension depend on? IMF and temperature of fluid -higher temp, weaker surface tension
For capillary action, which way is the water pulled when adhesive forces stronger? upward
For capillary action, which way is water pulled when cohesive forces are stronger? downward
What is stress? Stress = Force / Area -Force applied to object / area force is applied
What is strain? Strain = change in dimension / original dimension
Modulus of elasticity stress/ strain
What is yield point? maximum stress point
WHat happens beyond yield point? object will remain intact but will not regain original shape
What are the three moduli? 1.) Young's Modulus (tensile stress) - E 2.) Shear's Modulus (shear stress) - G 3.) Bulk modulus (compression and expansion) - B
Young's Modulus E = F/A // change in height / original height
Shear Modulus G = F/A // change in x / original height
Bulk Modulus B = change in Pressure // change in volume / original volume
What does density vary with? temperature and pressure
What does buoyant force equal to for object immersed in a fluid? weight of the fluid displaced by the object
What does it mean for something to be floating? weight = buoyant force
What are the forces that act on an object floating in water -weight and Fb in vertical direction -pressure perpendicular to all surfaces
Speed of flow rate for a fluid is directly / inversely proportional to cross - SA inversely proportional
Items with the same volume experience the same ___ buoyant force
How to calculate percent submerged? density object / density medium
Calculate specific gravity with weight and Fb? specific gravity = weight / Fb
Surface tension is an attractive / repulsive force? attractive
Within a pipe, where does fluid flow the slowest? fastest? edge of pipe / center of pipe
Greater flow rate is associated with? a greater pressure differential
According to Poiseuille's Principle, what are the main things to know? -Q = r^4 -Q = 1 / L
In a pipe, a lower area has a faster/slower speed while a bigger area has a faster/slower speed? slower / faster
does fluid flow faster or slower through a narrowed pipe? What happens to pressure? faster / decreases
Are narrow or wider paths more likely to encounter turbulence? wider
What does flow rate depend on? pressure differential
Elasticity progression. Elastic limit --> ultimate tension strength --> fracture
What are brittle materials? materials that have ultimate tension strengths close to fractures
What are ductile materials? materials that have ultimate tension strengths far from fractures
Does a thicker or thinner rope increase / decrease stretching length of the rope? increase
What is a large bulk modulus associated with? solid that is difficult to deform and compress
What is a large tensile modulus associated with? something that requires a lot of force to stretch
What is a large shear modulus associated with? something that requires a lot of force to shear
Comparing two objects with different masses but same volume, which will have the stronger buoyant force? bigger mass one
volume of an object submerged = volume of fluid displaced by object
Relate pressure, force, area P = F / A --> F1 / A1 = F2 / A2
TRUE / FALSE: In a hydraulic system, the work done on one end is different than the work output at the other. FALSE
Gauge pressure pgh
TRUE / FALSE: Volume flow rate of a fluid is constant TRUE
Does turbulence occur at low or high velocities? high
Out of solids, liquids, gases, which are compressible? gases
What is shear angle? tan-1(change in x / height)
When an object floats, the ratio of densities of object / medium is =? percent submerged
What is the magnitude of the weight equal to in relation to the apparent weight and buoyant force? weight = apparent weight + buoyant force
Relative densities for floating vs. submerged object? percent submerged vs. W/B ratio
Greater viscosity requires...? greater pressure differential
What does buoyant force also equal to? What does normal force equal to? apparent weight loss / apparent weight
What phases are held together by IMF? solids and liquids
What phases can withstand perpendicular forces? solid, liquid, gas
What phase can withstand forces NOT perpendicular? solid
What phase experiences large changes in density? gas
When air resistance is negligible, is projectile motion independent of mass? YES
What are the 2 densities of water? 1000kg/m^3 1g/cm^3
What depth of water creates 1 at of pressure? 10 m
Created by: 507935299

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