Glossary
Adiabatic process
A thermodynamic process in which no heat is exchanged between the system and its surroundings. Changes in internal energy are solely due to work done.
Example:
The rapid compression of air in a bicycle pump, causing it to heat up, is an approximation of an adiabatic process.
Classical Thermodynamics
A macroscopic approach to thermodynamics that describes the behavior of large systems using observable properties like pressure, volume, and temperature, without considering individual particles.
Example:
Predicting the final temperature of water after mixing hot and cold water is an application of classical thermodynamics.
Closed System
A thermodynamic system that can exchange energy (heat and work) with its surroundings but does not exchange matter.
Example:
A sealed, insulated thermos containing hot soup approximates a closed system as it exchanges heat but no soup with the outside.
Efficiency
A measure of how effectively a system converts input energy into useful output work or energy, expressed as a ratio or percentage.
Example:
A highly efficient solar panel converts a large percentage of incident sunlight into electrical energy.
Energy
The capacity to do work or produce heat. It exists in various forms, including kinetic, potential, thermal, and chemical.
Example:
A roller coaster at the top of a hill possesses gravitational potential energy before it begins its descent.
Engines
Devices that convert thermal energy into mechanical work, typically by exploiting temperature differences between a hot reservoir and a cold reservoir.
Example:
A car's internal combustion engine burns fuel to create hot gases that push pistons, generating motion.
Entropy
A measure of the disorder or randomness within a thermodynamic system, which tends to increase in isolated systems over time according to the Second Law of Thermodynamics.
Example:
When an ice cube melts into water, its molecules become more disordered, leading to an increase in entropy.
Gases
A state of matter characterized by particles that are widely dispersed, have high kinetic energy, and fill their container.
Example:
The air we breathe is a mixture of different gases, primarily nitrogen and oxygen.
Heat
The transfer of thermal energy between systems due to a temperature difference. It flows from hotter to colder regions.
Example:
When you touch a hot stove, the sensation of warmth is due to heat transferring from the stove to your hand.
Heat Pumps
Devices that use work to transfer heat from a colder outdoor environment to a warmer indoor space, or vice versa, for heating or cooling.
Example:
In winter, a heat pump can extract thermal energy from the cold outside air and transfer it inside to warm a building.
Ideal Gas Law
A fundamental equation of state for an ideal gas, relating pressure, volume, temperature, and the number of moles (PV=nRT).
Example:
Using the Ideal Gas Law, you can calculate the pressure inside a sealed container of gas if you know its volume, temperature, and the amount of gas.
Internal Energy
The total energy contained within a thermodynamic system, comprising the kinetic and potential energies of its constituent particles.
Example:
When you heat a pot of water, its internal energy increases as the water molecules move faster.
Isobaric process
A thermodynamic process that occurs at a constant pressure. Work done in such a process is simply pressure times the change in volume.
Example:
Heating a gas in a cylinder with a movable piston that maintains constant external pressure demonstrates an isobaric process.
Isochoric process
A thermodynamic process that occurs at a constant volume. In such a process, no work is done by or on the system.
Example:
Heating a gas inside a rigid, sealed container is an isochoric process because the volume cannot change.
Isothermal process
A thermodynamic process during which the temperature of the system remains constant. Any heat added or removed is balanced by work done by or on the system.
Example:
A gas expanding slowly in contact with a large heat reservoir can undergo an isothermal process.
Laws of Thermodynamics
Fundamental principles governing the transfer and transformation of energy, defining concepts like energy conservation, entropy, and absolute zero.
Example:
The operation of every engine and refrigerator is governed by the Laws of Thermodynamics.
Machines
Devices that use mechanical advantage or thermodynamic principles to perform work, often by converting one form of energy into another.
Example:
A simple lever is a machine that helps lift heavy objects with less force.
Object
A distinct physical entity with defined boundaries, often treated as a single point mass in simpler physics models.
Example:
In a simple mechanics problem, a bowling ball might be treated as a single object.
Open System
A thermodynamic system that can exchange both energy (heat and work) and matter with its surroundings.
Example:
A boiling pot of water on a stove is an open system because water vapor escapes (matter) and heat is added.
Pressure-Volume (PV) diagrams
Graphical representations that plot the pressure of a system against its volume, used to visualize thermodynamic processes and calculate work done.
Example:
Analyzing the cycle of a heat engine often involves tracing its path on a Pressure-Volume (PV) diagram.
Refrigerators
Devices that use work to transfer heat from a colder reservoir to a hotter reservoir, thereby cooling a space.
Example:
Your kitchen refrigerator continuously removes heat from its interior and expels it into the warmer room.
Statistical Thermodynamics
A microscopic approach to thermodynamics that explains macroscopic properties based on the statistical behavior and energy states of individual atoms and molecules.
Example:
Explaining why gases expand to fill their containers by considering the random motion of countless molecules falls under statistical thermodynamics.
Surroundings
Everything outside the defined thermodynamic system that can interact with the system by exchanging energy or matter.
Example:
For a cup of hot coffee, the air in the room and the cup itself are part of the surroundings.
System
A defined region of the universe chosen for study, separated from its surroundings by a real or imaginary boundary.
Example:
When analyzing a refrigerator, the interior cooling coils and the refrigerant gas within them constitute the thermodynamic system.
Thermodynamics
The branch of physics concerned with heat and its relation to other forms of energy and work. It describes how energy is transferred and transformed within systems.
Example:
Understanding how a car engine converts fuel into motion involves the principles of thermodynamics.
Work
Energy transferred when a force causes displacement, or in thermodynamics, energy transferred due to a change in volume against an external pressure.
Example:
A gas expanding against a piston performs work on its surroundings.