Thermodynamics Overview

Thermodynamics

Definition: The branch of physics that deals with heat, work, and energy.
Laws of Thermodynamics:
1. Zeroth Law: If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
2. First Law: Energy cannot be created or destroyed, only transformed (ΔU = Q - W).
3. Second Law: The entropy of an isolated system always increases; heat cannot spontaneously flow from cold to hot.
4. Third Law: As temperature approaches absolute zero, the entropy of a perfect crystal approaches zero.
Key Concepts:
- Heat (Q): Energy transferred due to temperature difference.
- Work (W): Energy transfer that results from a force acting over a distance.
- Internal Energy (U): Total energy contained within a system.
- Entropy (S): Measure of disorder or randomness in a system.
Processes:
- Isothermal: Constant temperature (ΔT = 0).
- Adiabatic: No heat transfer (Q = 0).
- Isobaric: Constant pressure.
- Isochoric: Constant volume.

Mechanical Properties of Fluids

Definition: Study of how fluids (liquids and gases) behave under various forces and conditions.
Key Concepts:
- Density (ρ): Mass per unit volume of a fluid.
- Pressure (P): Force exerted per unit area (P = F/A).
- Buoyancy: Upward force exerted by a fluid, described by Archimedes' principle.
Fluid Statics:
- Pascal's Principle: Change in pressure applied to an enclosed fluid is transmitted undiminished throughout.
- Hydrostatic Pressure: Pressure at a depth in a fluid due to the weight of the fluid above (P = ρgh).
Fluid Dynamics:
- Continuity Equation: A1V1 = A2V2 (conservation of mass).
- Bernoulli's Equation: Relates pressure, velocity, and height of a fluid in motion (P + ½ρv² + ρgh = constant).
Viscosity: Measure of a fluid's resistance to flow; affects how fluids move (dynamic and kinematic viscosity).
Laminar vs Turbulent Flow:
- Laminar Flow: Smooth, orderly fluid motion; low velocity.
- Turbulent Flow: Chaotic fluid motion; high velocity, mixing occurs.

Thermodynamics

Definition: Branch of physics focused on heat, work, and energy transformations.
Zeroth Law: Establishes thermal equilibrium; if two systems both interact with a third system and are balanced with it, they are also balanced with each other.
First Law: Requires the principle of conservation of energy; states that energy is transformed rather than created or destroyed, expressed mathematically as ΔU = Q - W, where ΔU is the change in internal energy, Q is heat added, and W is work done.
Second Law: States that in an isolated system, entropy (disorder) always increases, implying that heat naturally flows from hotter to cooler objects, not the reverse.
Third Law: As temperature nears absolute zero, the entropy of a perfect crystal approaches zero, indicating a state of perfect order.
Key Concepts:
- Heat (Q): Energy transferred due to a temperature difference between systems.
- Work (W): Energy transfer associated with a force moving an object over a distance.
- Internal Energy (U): Total energy (kinetic and potential) contained within a system.
- Entropy (S): Quantifies the level of disorder or randomness in a system, providing insight into spontaneous processes and equilibrium.
Thermodynamic Processes:
- Isothermal: Temperature remains constant throughout the process (ΔT = 0).
- Adiabatic: No heat exchange occurs with surroundings (Q = 0).
- Isobaric: Pressure remains constant during the process.
- Isochoric: Volume is held constant.

Mechanical Properties of Fluids

Definition: Examines the behavior of liquids and gases under various forces, emphasizing their response to pressure and flow changes.
Key Concepts:
- Density (ρ): Mass per unit volume of a fluid; fundamental property affecting buoyancy and flow.
- Pressure (P): Defined as force per unit area (P = F/A), critical for understanding fluid behavior.
- Buoyancy: Upward force exerted by a fluid, described by Archimedes' principle, which states that an object submerged in a fluid experiences a buoyant force equal to the weight of the fluid it displaces.
Fluid Statics:
- Pascal's Principle: Asserts that a change in pressure applied to an enclosed fluid is undiminished throughout the fluid; critical in hydraulic systems.
- Hydrostatic Pressure: Calculated as P = ρgh, where h is the depth in the fluid, representing the weight of the fluid above a given point.
Fluid Dynamics:
- Continuity Equation: A1V1 = A2V2 reflects the conservation of mass, illustrating that the flow rate must remain constant through varying cross-sectional areas.
- Bernoulli's Equation: Describes the relationship between pressure, velocity, and elevation in moving fluids (P + ½ρv² + ρgh = constant), supporting applications in fluid mechanics and aerodynamics.
- Viscosity: Indicates a fluid's resistance to flow; distinguished into dynamic viscosity (resistance during flow) and kinematic viscosity (dynamic viscosity divided by density).
Flow Types:
- Laminar Flow: Characterized by smooth and orderly fluid movement, typically at low velocities, where layers of fluid slide past one another.
- Turbulent Flow: Involves chaotic and irregular fluid motion, occurs at high velocities, leading to increased mixing and energy dissipation.