Fluids
60 flashcards covering Fluids for the MCAT Chem / Phys / Psych / Soc section.
Fluids are materials that can flow and change shape, encompassing liquids like water and gases like air. Unlike solids, fluids don't have a fixed form; they adapt to their containers while exerting forces such as pressure and buoyancy. This topic explores key principles like Pascal's law, Archimedes' principle, and fluid dynamics, which help explain everyday phenomena, from blood circulation in the body to atmospheric pressure. Mastering fluids builds a foundation for understanding physical systems in biology and medicine.
On the MCAT, fluids appear in the Chemical and Physical Foundations section, often through multiple-choice questions that test concepts like pressure differences, flow rates, and viscosity. Common traps include misapplying formulas, such as confusing static fluids with dynamic ones, or overlooking units in calculations. Focus on integrating physics with biological contexts, like how blood flow relates to heart function, and practice problem-solving to avoid errors in real-world scenarios. A solid grasp here can boost your score by linking these ideas to health sciences. For better retention, practice with timed questions involving Bernoulli's principle.
Terms (60)
- 01
Density
Density is the mass per unit volume of a substance, calculated as mass divided by volume, and is a key property in determining how fluids behave under various conditions.
- 02
Specific Gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance, usually water at 4°C, and helps compare the buoyancy of fluids.
- 03
Pressure
Pressure is the force exerted per unit area on a surface, and in fluids, it increases with depth due to the weight of the fluid above.
- 04
Atmospheric Pressure
Atmospheric pressure is the pressure exerted by the weight of the atmosphere, typically 101.3 kPa at sea level, and affects fluid systems like barometers.
- 05
Hydrostatic Pressure
Hydrostatic pressure is the pressure at a point in a fluid at rest, given by the formula P = ρgh, where ρ is density, g is gravity, and h is depth.
- 06
Gauge Pressure
Gauge pressure is the pressure measured relative to atmospheric pressure, commonly used in manometers to determine fluid levels in closed systems.
- 07
Absolute Pressure
Absolute pressure is the total pressure including atmospheric pressure, calculated by adding gauge pressure to atmospheric pressure in fluid dynamics problems.
- 08
Pascal's Principle
Pascal's principle states that pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid, as seen in hydraulic lifts.
- 09
Hydraulic Systems
Hydraulic systems use Pascal's principle to multiply force through confined fluids, allowing small inputs to produce large outputs in devices like car brakes.
- 10
Archimedes' Principle
Archimedes' principle states that the buoyant force on an object equals the weight of the fluid displaced by the object, determining whether it floats or sinks.
- 11
Buoyant Force
Buoyant force is the upward force exerted by a fluid on an immersed object, equal to the weight of the displaced fluid, and affects object stability in liquids.
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Submerged Objects
For submerged objects, the buoyant force depends on the fluid's density and the object's volume, and if it equals the object's weight, the object is neutrally buoyant.
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Floating Objects
Floating objects displace a volume of fluid equal to their own weight, as per Archimedes' principle, which is why ice floats on water.
- 14
Bernoulli's Equation
Bernoulli's equation relates pressure, velocity, and height in a flowing fluid, stating that the sum of pressure energy, kinetic energy, and potential energy is constant along a streamline.
- 15
Bernoulli's Principle
Bernoulli's principle explains that an increase in fluid speed occurs with a decrease in pressure, as seen in the lift on an airplane wing.
- 16
Continuity Equation
The continuity equation states that for an incompressible fluid, the product of cross-sectional area and velocity is constant, ensuring mass flow rate remains steady.
- 17
Viscosity
Viscosity is a fluid's resistance to flow, influenced by temperature and molecular interactions, and is measured in pascal-seconds for liquids like water or oil.
- 18
Newtonian Fluids
Newtonian fluids have a constant viscosity regardless of the applied shear stress, such as water, making their flow predictable in pipes and channels.
- 19
Non-Newtonian Fluids
Non-Newtonian fluids change viscosity with shear stress, like blood or ketchup, which can thicken or thin depending on flow conditions in medical contexts.
- 20
Poiseuille's Law
Poiseuille's law describes the flow rate of a viscous fluid through a cylindrical pipe, given by Q = (πr^4 ΔP) / (8ηL), where r is radius and η is viscosity.
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Laminar Flow
Laminar flow is a smooth, orderly fluid motion where layers slide past each other without mixing, occurring at low velocities in pipes.
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Turbulent Flow
Turbulent flow is chaotic and irregular fluid motion with eddies and mixing, typically occurring at high velocities, as in fast-moving rivers.
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Reynolds Number
Reynolds number is a dimensionless quantity that predicts flow regime, calculated as Re = (ρvd)/η, where flow is laminar if Re < 2000 and turbulent if Re > 4000.
- 24
Venturi Effect
The Venturi effect describes how fluid speed increases and pressure decreases in a constricted section of a pipe, used in devices like carburetors.
- 25
Manometer
A manometer measures pressure differences in fluids using a U-shaped tube with liquid, where the height difference corresponds to the pressure.
- 26
Barometer
A barometer measures atmospheric pressure using a column of mercury, with variations indicating weather changes or altitude effects.
- 27
Surface Tension
Surface tension is the property of a liquid's surface that resists external force due to cohesive forces between molecules, causing droplets to form spheres.
- 28
Capillary Action
Capillary action is the ability of a liquid to flow in narrow spaces without gravity's help, due to adhesive and cohesive forces, as in plant water transport.
- 29
Cohesion
Cohesion is the intermolecular attraction between like molecules in a fluid, contributing to surface tension and the shape of liquid drops.
- 30
Adhesion
Adhesion is the attraction between unlike molecules, such as a liquid and a solid surface, which enables capillary rise in narrow tubes.
- 31
Osmosis
Osmosis is the diffusion of water across a semi-permeable membrane from low to high solute concentration, essential for cell function and fluid balance.
- 32
Osmotic Pressure
Osmotic pressure is the pressure required to stop osmosis, calculated using π = iMRT for solutions, and is crucial in biological and chemical contexts.
- 33
Diffusion
Diffusion is the net movement of particles from high to low concentration due to random molecular motion, affecting how substances mix in fluids.
- 34
Ideal Fluid
An ideal fluid is incompressible, has no viscosity, and flows steadily, simplifying theoretical models in fluid dynamics problems.
- 35
Real Fluid
A real fluid has viscosity, compressibility, and turbulence, making its behavior more complex than an ideal fluid in practical applications.
- 36
Stokes' Law
Stokes' law gives the drag force on a sphere moving through a viscous fluid, F = 6πηrv, used to calculate terminal velocity of small particles.
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Terminal Velocity
Terminal velocity is the constant speed reached by an object falling through a fluid when drag force equals gravitational force, as in sedimentation.
- 38
Hydrostatic Equilibrium
Hydrostatic equilibrium occurs when the pressure gradient in a fluid balances the gravitational force, maintaining stability in stars or Earth's atmosphere.
- 39
Equation of Continuity
The equation of continuity for fluids states that the mass flow rate is constant, leading to A1v1 = A2v2 for incompressible flows.
- 40
Torricelli's Theorem
Torricelli's theorem relates the speed of efflux from a hole in a tank to the height of the fluid above, given by v = √(2gh).
- 41
Speed of Efflux
Speed of efflux is the velocity at which fluid exits an orifice, determined by the height of the fluid column and gravity, as in water jets.
- 42
Hydraulic Press
A hydraulic press uses Pascal's principle to amplify force through a larger piston, commonly used in industrial applications for compressing materials.
- 43
Blood Pressure
Blood pressure is the force exerted by circulating blood on vessel walls, measured in mmHg, and involves fluid dynamics in the cardiovascular system.
- 44
Poise
Poise is the unit of dynamic viscosity in the CGS system, equal to one gram per centimeter per second, used to quantify fluid resistance.
- 45
Fluid Resistance
Fluid resistance is the opposition to motion through a fluid, primarily due to viscosity and drag, affecting objects like projectiles in air or water.
- 46
Pitot Tube
A Pitot tube measures fluid velocity by converting kinetic energy to pressure, used in aviation to determine airspeed.
- 47
Vapor Pressure
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid, influencing boiling points and evaporation in fluid systems.
- 48
Raoult's Law
Raoult's law states that the vapor pressure of a solvent in a solution is the pure solvent's vapor pressure times its mole fraction, affecting solution behavior.
- 49
Colligative Properties
Colligative properties depend on the number of solute particles in a solution, including boiling point elevation and osmotic pressure in fluids.
- 50
Boiling Point Elevation
Boiling point elevation is the increase in a solvent's boiling point due to dissolved solutes, a colligative property in aqueous solutions.
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Freezing Point Depression
Freezing point depression is the lowering of a solvent's freezing point by solutes, another colligative property relevant to fluid mixtures.
- 52
Solubility
Solubility is the maximum amount of solute that can dissolve in a solvent at a given temperature, determining fluid mixture stability.
- 53
Molarity
Molarity is the concentration of a solution measured as moles of solute per liter of solution, used in fluid chemistry calculations.
- 54
Common Trap: Units of Pressure
A common trap is confusing units like atm, mmHg, and Pa; remember to convert consistently, as 1 atm equals 760 mmHg or 101.3 kPa.
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Common Trap: Buoyancy Calculation
A common trap in buoyancy problems is forgetting to account for the fluid's density; always use the correct value for accurate force determination.
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Strategy for Bernoulli Problems
For Bernoulli problems, identify points along a streamline, apply the equation, and conserve energy while considering assumptions like incompressible flow.
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Worked Example: Hydrostatic Pressure
In a worked example, calculate the pressure at 10 meters depth in water: P = ρgh = (1000 kg/m³)(9.8 m/s²)(10 m) = 98,000 Pa, showing depth's effect.
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Worked Example: Buoyant Force
For a 5 kg object submerged in water, buoyant force equals the weight of displaced water: if volume is 0.005 m³, force = (1000 kg/m³)(0.005 m³)(9.8 m/s²) = 49 N.
- 59
Advanced: Compressible Fluids
In advanced fluid dynamics, compressible fluids like gases require accounting for density changes with pressure, unlike incompressible liquids in basic problems.
- 60
Advanced: Viscosity Effects
Viscosity effects become significant in narrow tubes, where Poiseuille's law shows flow rate is highly sensitive to radius, as in blood vessels.