Concise Physics Handbook

Formulas for Key Sections

Kinetic Theory of Matter

a physical theory explaining the properties and behavior of matter through the motion and interaction of its smallest particles: atoms, molecules, and ions.

1. Basic Provisions of the Molecular Kinetic Theory

Molecular Concentration:

Formula for molecular concentration: n = N / V — ratio of number of molecules to volume

n= NV
What does this formula mean?

n — concentration of particles (molecules) per unit volume. It is used to calculate pressure and other macroscopic quantities in a gas.

Basic MKT Equation:

Formula for ideal gas pressure: P = (1/3)·m·n·v²̄ — relation of pressure to mass, concentration, and mean square velocity of molecules

P= 13· m·n· v2¯
Physical Meaning

Gas pressure is explained by molecular collisions with the walls.
m — mass of one particle, v²̄ — mean square velocity, n — concentration. This equation relates microscopic parameters to macroscopic pressure.

Kinetic Energy of a Single Particle:

Formula for kinetic energy: K = (1/2)·m·v² — energy of motion of a particle with mass m and velocity v

K= 12· m·v2
What does energy mean?

This is the mechanical energy of translational motion of a single particle. v — instantaneous velocity of the molecule.

Alternative: Pressure through Energy:

Formula for pressure through average kinetic energy: P = (2/3)·n·K̄

P= 23· n· K¯
Physical Interpretation

— average kinetic energy of a particle. This form shows that pressure is proportional to the energy of molecules.

Temperature as a Measure of Energy:

Formula for average kinetic energy of molecules: K̄ = (3/2)·k·T — temperature is proportional to the average kinetic energy of particle motion

K¯= 32· k·T
Physical Meaning

Temperature is proportional to the average kinetic energy of particle motion. k — Boltzmann constant. The formula is fundamental for connecting MKT with thermodynamics.

2. Kinetic Theory of Ideal Gas

Kinetic Energy of a Single Particle:

Formula for kinetic energy: W = (1/2)·m₀·v² — energy of motion of a particle with mass m₀ and velocity v

W= 12· m0· v2
Meaning of this formula

m₀ — mass of one molecule, v — instantaneous velocity. This is the basis for deriving pressure and average energy of a gas.

Pressure through Average Energy:

Formula for ideal gas pressure: p = (2/3)·n·W̄ — pressure is proportional to molecular concentration and their average kinetic energy

p= 23·n· W¯
Physical Interpretation

The pressure of an ideal gas is directly proportional to the average kinetic energy of its molecules. The formula is derived based on modeling the chaotic motion of molecules.

Average Kinetic Energy and Temperature:

Formula for the relationship between average kinetic energy of molecules and temperature: W̄ = (3/2)·k·T

W¯= 32· k·T
Why is this needed?

Gas temperature serves as a measure of the average kinetic energy of its molecules. This is a fundamental relationship between macro and micro parameters.

Particle Velocity through Molar Mass:

Formula for root-mean-square velocity of molecules: v = √(3RT / μ) — depends on temperature, gas constant, and molar mass

v= 3·R·T μ
Interpretation

The formula allows finding the average velocity of molecules at a given temperature. μ — molar mass of the gas, R — universal gas constant.

3. Equation of State

General Equation of State:

Formula for ideal gas state: p·V = N·k·T = n·R·T — relationship between pressure, volume, temperature, number of particles, and amount of substance

p·V= N·k·T= n·R·T
What does this mean?

Connects macroscopic gas parameters: pressure, volume, and temperature — with micro parameters: number of particles N or amount of substance n. The formula comes in two forms:
Microscopic: pV = NkT
Macroscopic: pV = nRT

Equation Form via Gas Mass:

Formula for ideal gas state via mass: p·V = (m / μ)·R·T — relationship between pressure, volume, and temperature with gas mass and molar mass

p·V= mμ·R·T
Interpretation

m — mass of the gas, μ — its molar mass. The formula is useful for calculations with a given mass of substance.

Constants Relationship:

Formula for the relationship between the universal gas constant, Avogadro's number, and Boltzmann constant: R = NA·k

R= NA·k
Why is this needed?

This relationship allows transitioning from micro parameters (via k) to macro forms (via R). NA — Avogadro's constant.

4. Molecular Velocities

Mean Square Velocity of Molecules:

Formula for mean square velocity of molecules: v²̄ = (3·k·T) / m₀ — depends on temperature, Boltzmann constant, and mass of one molecule

v2¯= 3·k·T m0
What does this formula provide?

Allows calculating the average kinetic activity of molecules at a given temperature. k — Boltzmann constant, m₀ — mass of one molecule.

Effective (RMS) Velocity of Molecules:

Formula for effective (root-mean-square) velocity of molecules: vrms = √(v²̄) — square root of the mean square velocity

vrms= v2¯
Meaning of RMS velocity

This is the square root of the mean square velocity. Used in calculations of pressure, momentum, heat flux. The higher the temperature — the higher vrms.

Velocity through Molar Mass:

Formula for root-mean-square velocity of molecules: v = √(3·R·T / μ) — depends on temperature, universal gas constant, and molar mass

v= 3·R·T μ
What does this form mean?

Shows the dependence of the average velocity on temperature and molar mass of the gas. Useful for calculations where μ — the molar mass of the substance — is given.