Physical system
Introduction
A physical system is a portion of the physical universe chosen for analysis. Everything outside the system is known as the environment. The environment is ignored except for its effects on the system. The cut between system and the world is a free choice, generally made to simplify the analysis as much as possible. A system can be as large as a planet or as small as a single atom.
Classification of Physical Systems
Physical systems can be classified in several ways, such as by their state or by their properties. Here are some of the most common classifications:
Open, Closed, and Isolated Systems
Physical systems can be classified as open, closed, or isolated based on whether energy and matter can enter or leave the system.
- An open system is one in which both energy and matter can enter and leave the system. An example of an open system is a pot of boiling water on a stove. Heat energy and water vapor can leave the system, and heat energy can enter the system from the stove.
- A closed system is one in which energy can enter and leave the system, but matter cannot. An example of a closed system is a sealed container of gas. The gas cannot leave the container, but heat energy can be added or removed.
- An isolated system is one in which neither energy nor matter can enter or leave the system. An example of an isolated system is a thermos bottle containing hot coffee. Ideally, no heat energy or coffee can enter or leave the thermos.
Homogeneous and Heterogeneous Systems
Physical systems can also be classified as homogeneous or heterogeneous based on whether the system's properties are the same throughout the system.
- A homogeneous system is one in which the properties are the same throughout the system. An example of a homogeneous system is a container of pure water. The water's properties, such as its density and temperature, are the same throughout the container.
- A heterogeneous system is one in which the properties vary throughout the system. An example of a heterogeneous system is a container of oil and water. The oil and water do not mix, so the properties of the system vary depending on whether you are looking at the oil or the water.
Dynamics of Physical Systems
The dynamics of a physical system refer to how the system changes over time. This can be described by a set of differential equations known as the system's dynamical equations. These equations describe how the system's state changes over time based on the system's current state and the forces acting on the system.
For example, consider a simple pendulum. The pendulum's dynamical equations describe how the pendulum's angle and angular velocity change over time based on the pendulum's current angle and angular velocity and the force of gravity acting on the pendulum.
Thermodynamics of Physical Systems
The thermodynamics of a physical system refer to the study of energy and heat transfer in physical systems. Thermodynamics can be used to predict how a system will respond to changes in its environment, such as changes in temperature or pressure.
For example, consider a gas in a container. The gas's thermodynamic state can be described by its temperature, pressure, and volume. If the gas's temperature is increased, the gas's pressure and volume will also increase. This is described by the ideal gas law, a fundamental equation in thermodynamics.
Quantum Mechanics of Physical Systems
The quantum mechanics of a physical system refer to the study of physical systems at the atomic and subatomic level. Quantum mechanics is fundamentally different from classical physics, and it provides a more accurate description of the behavior of physical systems at these small scales.
For example, consider an electron in an atom. The electron's state can be described by a wavefunction, which gives the probability of finding the electron in different locations around the atom. The electron's behavior is governed by the Schrödinger equation, a fundamental equation in quantum mechanics.