Fluids
Fluids are substances that have the ability to flow and conform to the shape of their containers.
Fluids can exert _____ forces, but cannot exert _____ forces.
perpendicular
shear
_____ and _____ are the two phases of matter that are fluids.
Liquids and gases
Solids
Solids do not flow and they retain their shape regardless of their containers.
Density
Density is the mass per unit volume of a substance (fluid or solid).
Pressure
Pressure is defined as a measure of force per unit area.
Pressure is exerted by a fluid on _____ and on _____.
the walls of its container
objects placed in the fluid
Pressure is a _____ quantity
scalar
The pressure exerted by a gas against the walls of its container will always be _____ to the container walls.
perpendicular (normal)
Absolute pressure
Absolute pressure is the sum of all pressures at a certain point within a fluid
Absolute pressure is equal to _____ plus _____.
the pressure at the surface of the fluid (usually atmospheric pressure)
the pressure due to the fluid itself
Gauge pressure
Gauge pressure is the name for the difference between absolute pressure and atmospheric pressure.
In liquids, gauge pressure is caused by ...
... the weight of the liquid above the point of measurement.
Pascal’s principle
Pascal’s principle states that a pressure applied to an incompressible fluid will be distributed undiminished throughout the entire volume of the fluid
Hydraulic machines
Hydraulic machines operate based on the application of Pascal’s principle to generate mechanical advantage.
Archimedes’ principle
When an object is placed in a fluid, the fluid generates a buoyant force against the object that is equal to the weight of the fluid displaced by the object.
The direction of the buoyant force is always ...
... opposite to the direction of gravity.
If the maximum buoyant force is _____, the object will float. This will be true if the object is _____ than the fluid it is in.
larger than the force of gravity on the object
less dense
If the maximum buoyant force is _____, the object will sink. This will be true if the object is _____ than the fluid it is in.
smaller than the force of gravity on the object
more dense
Cohesive forces
Fluids experience cohesive forces with other molecules of the same fluid.
Adhesive forces
Fluids experience adhesive forces with other materials.
Cohesive forces give rise to _____.
surface tension
Fluid dynamics
Fluid dynamics is a set of principles regarding actively flowing fluids.
Viscosity
Viscosity is a measurement of a fluid’s internal friction.
Viscous drag
Viscous drag is a nonconservative force generated by viscosity.
Fluids can move with either _____ or _____.
laminar flow or turbulent flow.
The rate of laminar flow is determined by the relationships in _____.
Poiseuille’s law
On the MCAT, incompressible fluids are assumed to have _____ and _____ while flowing, allowing us to assume _____.
laminar flow and very low viscosity
conservation of energy
Continuity equation
The continuity equation is a statement of the conservation of mass as applied to fluid dynamics.
Bernoulli’s equation is an expression of _____ for a flowing fluid.
conservation of energy
Bernoulli’s equation
Bernoulli’s equation states that the sum of the static pressure and the dynamic pressure will be constant between any two points in a closed system.
For a horizontal flow, there is an _____ relationship between pressure and speed.
inverse
Venturi effect
In a closed system, there is a direct relationship between cross-sectional area and pressure exerted on the walls of the tube known as the Venturi effect.
The circulatory system behaves as a _____ with _____ flow.
closed system
nonconstant
Resistance _____ as the total cross-sectional area increases.
decreases
Arterial circulation is primarily motivated by _____.
the heart
Venous circulation has _____ the volume of arterial circulation.
three times
Venous circulation is motivated by _____.
the skeletal musculature and expansion of the heart.
Inspiration and expiration create a pressure gradient not only for the _____, but for the _____ as well.
respiratory system
circulatory system
Air at the alveoli has _____.
essentially zero speed