The understanding that heat is related to the vibrations of particles within an object comes from the kinetic theory of matter and statistical mechanics. While it is challenging to directly "see" the vibrations of individual particles, there is compelling evidence and theoretical understanding that support this concept. Here are a few lines of evidence:
Temperature and Energy Transfer: When two objects at different temperatures come into contact, heat flows from the hotter object to the colder one until thermal equilibrium is reached. This phenomenon is explained by the kinetic theory of matter, which states that heat transfer occurs due to the transfer of kinetic energy from faster-moving particles to slower-moving ones. This transfer of energy is associated with the vibrations, rotations, and translations of particles within the material.
Expansion and Contraction: When a substance is heated, it tends to expand, and when it is cooled, it contracts. This behavior can be understood by considering that as the substance is heated, the particles vibrate more vigorously, increasing the average separation between them and causing the material to expand. Conversely, cooling leads to a decrease in particle vibrations and a decrease in average separation, resulting in contraction.
Specific Heat Capacity: Specific heat capacity is a property of materials that quantifies the amount of heat energy required to raise the temperature of a given mass of the substance by a certain amount. The concept of specific heat capacity aligns with the idea that heat energy is associated with the vibrations of particles within a substance. The energy is absorbed by the particles, increasing their kinetic energy and, therefore, their vibrational motion.
Spectroscopy: Spectroscopic techniques, such as infrared spectroscopy, can provide information about the vibrational modes of molecules. By analyzing the energy levels and transitions of molecules, scientists can identify and characterize the vibrational motions of the atoms within a substance.
While these lines of evidence support the understanding that heat is related to the vibrations of particles, it is important to note that this explanation is based on theoretical models and indirect observations. The microscopic nature of heat and the vibrations of particles are best understood within the framework of statistical mechanics and quantum mechanics, which provide a more detailed understanding of the behavior of atoms and molecules.