Chapter 5: Fluids and Solids Flashcards
Fluid definition:
has the ability to flow and conform to the shape of the container
Solid definition:
does not flow and its rigidity helps it retain a shape independent of that of any container
Liquids and gases are both:
fluids
Density equation:
p = m/v
a scalar quantity; units = kg/m3 or g/mL or g/cm3
How many liters are in a cubic meter?
1000
Equation to determine the weight of any volume of a given substance:
W = ρVg
where p is the density and V is the volume of the substance
Specific gravity:
the ratio of the density of a substance to that of pure water at 1 atm and 4 degrees Celsius; if it is less than one the object will float; if it is greater than one the object will sink
Density of water:
1,000 kg/m3 or 1 g/cm3
Pressure is:
the force per unit of area; it is exerted by a fluid on the walls of its container and on objects placed in the fluid
Equation to determine pressure:
P = F/A
where F is the normal force and A is the area; a scalar quantity; units = Pa = N/m2
Pressure conversions:
1.013 X 105 Pa = 1 atm = 760 torr = 760 mmHg
Absolute pressure is:
the sum of all pressure at a certain point within a fluid; it is equal to the pressure at the surface of the fluid (liquid or gas) plus the pressure due to the fluid itself
Equation to determine absolute pressure:
P = Po + ρgh
where P is the absolute pressure, Po is the pressure at the surface, and ρgh is (density fluid above)(gravity)(height of submerged object below surface)
units = N/m2
Gauge pressure is:
the difference between the surface pressure and the absolute pressure
Equation to determine gauge pressure:
Pg = P - Patm = (Po + ρgh) - Patm
units = Pa
Forces and fluids:
fluids can exert perpendicular forces, but cannot withstand shear forces
On the MCAT, liquids are assumed to be:
incompressible and are ideal conservative systems
Forces and solids:
solids can exert perpendicular forces and can withstand shear forces
If mass is held constant in the density equation, what is the relationship between volume and density?
inverse
During thermal expansion, what happens to density and volume?
density decreases as volume increases
The pressure exerted by a gas against that walls of its container will always be:
perpendicular to the container walls
Hydrostatics is:
the study of fluids at rest and the forces and pressures associated with standing fluids
Pascal’s principle states that:
an applied pressure to an incompressible fluid will be distributed undiminished throughout the entire volume of the fluid; hydraulic machines operate based on this principle
Equation of Pascal’s principle for incompressible fluids in containers:
P = F1/A1 = F2/A2
V = A1d1 = A2d2
W = F1d1 = F2d2
Area of a piston:
πr2
(the surface of a piston is circular)
Equation to determine the buoyant force on a floating object:
Fbuoy = (Vfluid displaced)(pfluid)(g) = weight of the object
units = (kg)(m/s2)
Equation to determine the buoyant force on a fully submerged object:
Fbuoy = (Vobject submerged)(pfluid)(g)
units = (kg)(m/s2)
When an object is placed in a fluid, it will sink until:
the point at which the volume of displaced fluid exerts a force that is equal to the weight of the object
An object’s specific gravity represented as a percentage directly indicates:
the percentage of the object’s volume that is submerged in the fluid
The direction of buoyant force is always:
opposite the direction of gravity
Surface tension results from:
cohesion (the attractive force that a molecule of liquid feels toward other molecules of the same liquid)
Adhesion:
the attractive force a molecule of liquid feels toward the molecules of some other substance (causes a meniscus)
A meniscus curved upward forms when:
the adhesive forces between the liquid and the container are greater than the cohesive forces of the liquid
A backward meniscus forms when:
the adhesive forces between the liquid and the container are less than the cohesive forces of the liquid
Viscosity is:
the resistance of a fluid to flow; can be thought of as fluid friction; the higher the viscosity, the slower the flow
Low-viscosity fluids have low internal resistance and behave more like:
ideal fluids (which have no viscosity)
SI unit of viscosity:
(N)(s/m2)
The two types of fluid flow:
laminar (smooth and orderly) and turbulent (rough and disorderly)
Equation to determine the critical velocity (Vc) of a fluid flowing through a tube:
vc = NRη/ρD
where NR is a given constant; η is the viscosity of the fluid, ρ is the density of the fluid, and D is the diameter of the tube
units = m/s
Streamines:
indicate the pathway followed by fluid particles as they move; velocity vector always tangentil to streamline; streamlines never cross each other
For a closed system, the volumetric rate of flow is:
constant and independent of changes in cross sectional area (the amount of water flowing past a point in a given amount of time is constant regardless of the width of the tube)
Fluids move more quickly through — passages and more slowly through — passages.
more quickly through narrow passages and more slowly through wider passages (continuity equation)
The continuity equation:
v1A1 = v2A2 = constant (the rate of flow)
Bernouli’s equation (an expression of conservation of energy for a flowing fluid):
P1 + 1/2ρv12 + ρgy1 = P2 + 1/2ρv22 + ρgy2
For horizontal flow, there is an inverse relationship between:
pressure and velocity
Elasticity of solids:
a measure of the response of a solid to an application of pressure; depending on the particular way in which the pressure is exerted, the object may experience a change in length, volume, or lateral displacement known as shear
Stress on a solid is:
a measurement of the pressure (F/A) applied to the solid
Strain on a solid is:
the degree to which the solid deforms under pressure
Equation to determine Young’s Modulus (perpendicular application of force):
Y = (F/A) / (∆L/L)
it gives the change in length of a solid when a pressure is applied perpendicularly to it (compression or stretching)
Elastic limits of a solid:
the degree to which an object can be compressed or stretched before it is permanently deformed or ruptured
Yield strength of a solid is:
the point of shape change beyond which a material will not return to its original dimensions once the applied force is removed
Ultimate strength of a solid is:
the point at which enough stress is applied to a solid object that it ruptures
Equation to determine Shear Modulus (parallel application of force):
S = (F/A) / (x/h)
where x is the lateral displacement and h is the vertical displacement
In both Young’s modulus and Shear modulus, the ratio is:
(stress) / (strain)
stress is always represented as pressure (F/A)
Equation to determine Bulk modulus (chage in volume due to pressure):
B = (F/A) / (∆V/V)
where V is volume
Relationship between the speed of sound and the Bulk modulus:
the speed of sound is proportional to the square root of the bulk modulus; sounds travel fastest through solids (highest bulk modulus) and slowest through gases (lowest bulk modulus)
Bernoulli’s equation states the the sum of — and — will be constant between any two points in a closed system.
static pressure and dynamic pressure
