Thermalbewegung

Thermalbewegung, or thermal motion, is the random movement of microscopic particles that arises from thermal energy. It is a fundamental concept in thermodynamics and statistical mechanics and is observed in gases, liquids, and solids as atoms and molecules continuously collide and exchange energy. In gases the motion is relatively free, while in liquids and solids it is constrained by intermolecular forces, leading to lattice vibrations in crystals and diffusion of particles in a fluid.

A prominent observable manifestation is Brownian motion: the erratic trajectory of small particles suspended in a fluid caused by constant collisions with surrounding molecules. Brownian motion provided empirical support for molecular theory and helped establish kinetic models of diffusion. The motion of microscopic constituents can be described statistically by equations such as the Langevin or Fokker-Planck formalisms, which account for random forces and friction.

Quantitatively, thermal motion is governed by temperature through the equipartition theorem. On average, each degree of freedom contributes (1/2)k_B T to the energy, so particle kinetic energy scales with temperature. This yields a root-mean-square speed roughly proportional to sqrt(k_B T / m). In fluids, thermal motion drives diffusion, and relations such as D = μ k_B T connect diffusion coefficients to mobility.

Thermalbewegung underpins many processes in physics, chemistry, and materials science, including diffusion, heat transfer, phase transitions, and chemical kinetics. In research and applications, thermal fluctuations are often modeled as random forces consistent with the system’s temperature, bridging microscopic motion and macroscopic behavior.