Internal energy of a body is the part of its total energy caused only by internal processes and interactions between substance particles. It consists of potential and kinetic energy of particles.
Internal energy of a body
Internal energy of any body is connected with the movement and a condition of particles (molecules, atoms) of substance. If the total energy of a body is known, then internal it is possible to find, having excluded from full the movement of all body as macroscopic object and also energy of interaction of this body with potential fields.
Also internal energy comprises energy of molecular vibrations and potential energy of intermolecular interaction. If it is about ideal gas, then the kinetic component gives the main contribution to internal energy. Total internal energy is equal to the sum of energy of separate particles.
It is known that kinetic energy of progress of a material point which models a substance particle strongly depends on the speed of its movement. Also it is worth noticing, as energy of oscillating and rotary motions depends on their intensity. Remember from a course of molecular physics a formula for internal energy of ideal one-atomic gas. She says through the sum of kinetic components of all of particles of gas which can be averaged. Averaging on all particles results in obvious dependence of internal energy on body temperature and also on quantity of degrees of freedom of particles. In particular, for one-atomic ideal gas which particles have only three degrees of freedom of progress the internal energy appears directly proportional constant of Boltzmann of three second works and temperature.
Dependence on temperature
So, internal energy of a body actually displays kinetic energy of the movement of particles. To understand what communication of this energy with temperature, it is necessary to define the physical meaning of size of temperature. If to heat the vessel filled with gas and having mobile walls, then its volume will increase. It means that pressure increased inside. Pressure of gas is created due to blows of particles about vessel walls. Time pressure increased, so also blow force increased that speaks about growth of speed of motion of the molecules. Thus, increase in temperature of gas led to increase in speed of motion of the molecules. In it temperature size essence also consists. Now it becomes clear that the increase in temperature leading to growth of speed of the movement of particles involves increase in kinetic energy of the intramolecular movement, so, and increase in internal energy.