Physics
Key properties within fluid dynamics, the study of fluids in motion, include density, which measures mass per volume of material, and viscosity, or the thickness of a fluid. Flow rate, or Q, describes how much fluid is moving and is determined by both the velocity of a fluid and the cross-sectional area it's flowing through.
Fluids (liquids or gases) can flow in two distinct ways: laminar or turbulent. Laminar flow is characterized by smooth, clean streamlines, while turbulent flow has swirls and eddies. The Reynolds Number can be calculated to figure out which form of flow is present in a given situation. For laminar flows, Poiseuille's Law can calculate the flow rate from the viscosity of the fluid, the radius and length of the cylinder, and the pressure differential driving the flow. Bernoulli's Equation enables determining how a flow will change if the cylinder carrying the flow changes its size or height, while the Venturi Effect illustrates the inverse relationship between fluid velocity and pressure.
Lesson Outline
<ul> <li>Fundamental properties of fluids <ul> <li>Density (ρ): Mass per unit volume, typically in kg/m³</li> <li>Viscosity (η): Measure of a fluid's resistance to shear or flow, typically in Pa·s</li> </ul> </li> <li>Flow rate (Q) <ul> <li>Defined as the volume of fluid passing a point per unit time (Q=V⋅A), where V is velocity and A is the cross-sectional area</li> </ul> </li> <li>Continuity equation <ul> <li>Based on the principle of conservation of mass in fluid flow: A1V1 = A2V2, where A1 and V1 are the area and velocity at point 1, and A2 and V2 are the area and velocity at point 2</li> </ul> </li> <li>Types of flow <ul> <li>Laminar flow: Fluid flows in parallel layers with no disruption between them</li> <li>Turbulent flow: Irregular, chaotic fluid motion characterized by velocity fluctuations</li> <li>Reynolds Number (Re): Dimensionless quantity used to predict flow patterns. Re = ρVD/η, where V is velocity, D is the characteristic length (e.g., diameter), and ρ and η are the density and viscosity of the fluid</li> </ul> </li> <li>Poiseuille's law <ul> <li>Describes laminar flow in a long, cylindrical pipe: ΔP = 8ηLQ/πr⁴, where ΔP is the pressure difference, η is the viscosity, L is the length of the pipe, Q is the flow rate, and r is the radius of the pipe</li> </ul> </li> <li>Bernoulli's Equation <ul> <li>Based on conservation of energy: P + ½ρv² + ρgh = constant, where P is the pressure, ρ is the density, v is the velocity, g is the acceleration due to gravity, and h is the height above a reference point</li> <li>Types of energy in fluids <ul> <li>Kinetic energy (½ρv²): Energy due to motion</li> <li>Gravitational potential energy (ρgh): Energy due to position in a gravitational field</li> <li>Pressure energy (P): Energy stored in a fluid due to applied pressure</li> </ul> </li> <li>Counterintuitive results <ul> <li>Increased speed means decreased pressure (Bernoulli's principle)</li> </ul> </li> <li>Venturi Effect <ul> <li>Pressure decreases in constricted section of a cylinder due to increased velocity (a direct application of Bernoulli's principle)</li> <li>Real-world implications: understanding blood flow in blocked arteries</li> </ul> </li> </ul> </li> </ul>
Don't stop here!
Get access to 29 more Physics lessons & 8 more full MCAT courses with one subscription!
FAQs
Laminar flow is characterized by the smooth, orderly movement of fluid particles in parallel layers with little to no mixing between them. This type of flow occurs at low velocities and low Reynolds Numbers. In contrast, turbulent flow is characterized by chaotic, rapidly changing fluid particle movements with significant mixing between layers. Turbulent flow occurs at high velocities and high Reynolds Numbers.
Viscosity is a measure of a fluid's resistance to deformation or flow. A fluid with higher viscosity will be more resistant to flow and will require more force to move it. In medical applications, viscosity is important in understanding the flow of biological fluids such as blood, mucus, and synovial fluid. Changes in viscosity can be indicative of certain medical conditions, such as increased blood viscosity in cardiovascular diseases or decreased synovial fluid viscosity in joint disorders.
Poiseuille's law describes the relationship between flow rate, pressure, viscosity, and vessel diameter in a laminar fluid flow through a cylindrical pipe. According to the law, flow rate is directly proportional to the pressure difference and the fourth power of the vessel radius, and inversely proportional to the fluid viscosity and the length of the pipe.
Bernoulli's Equation is a fundamental principle of fluid dynamics that describes the conservation of energy in an incompressible fluid flow. It states that the sum of kinetic energy, potential energy, and pressure energy remains constant along a streamline.
The Venturi effect is a phenomenon in fluid dynamics where a fluid's velocity increases and pressure decreases as it flows through a constricted section of a pipe or tube. This effect is derived from Bernoulli's Equation and is utilized in various medical devices such as nebulizers and Venturi masks.
