HEAT

A microscopic approach to the concept of Heat as energy transferred between two ideal gases held in contact.
Differences between Heat and Internal Energy.

Heat refers to an energy in transit between two systems held in contact that are at different temperatures.

The word heat is used in ordinary language with a meaning different from the previous definition. This often causes the student to approach this concept starting from a wrong idea.

EXPERIENCE: Energy transfer between two bodies at different temperature

Energy transfer  

Consider two systems A and B (for instance, two ideal gases) made up of 200 and 100 particles, respectively. System A (white particles) possess a certain internal energy and temperature, as shown in the corresponding windows. System B (red particles) has zero internal energy, and then its temperature is zero.

Two systems will be said to be in thermal contact when their particles are allowed to collide between them, and therefore can exchange energy. The proposed situation is certainly an extreme case, as the particles of B are at rest, which corresponds to the absolute zero temperature. Moreover, the systems are two-dimensional in order to get a most efficient interaction between the particles.

The distance between the two systems is controlled through the slider "Distance", initially at 100. Slide it until the value 0 is reached, when thermal contact will be achieved. The collisions between particles of both systems result in system A giving some energy to system B. The energy transferred in this way is the Heat Q exchanged between the two systems. Record the initial value of the energy of system A, and compare it with the final values of the energies in both systems.

See the explanation by clicking here.

A transfer of energy at a microscopic level has taken place. We understand by "transfer of energy at a microscopic level" the transfer of energy that take place because two bodies are in thermic contact, the particles of a system can collide with the particles of the other system so those with higher energy, higher temperature, will give energy to those particles of the system with lower temperature, this transfer will stop when both systems reach the same average energy: the same temperature.

HEAT - TEMPERATURE - INTERNAL ENERGY

These three concepts are clearly different, though there exist relations between them. An experience is proposed to help in the understanding of the following ideas:

EXPERIENCE:

Run the simulation, carry out the following experiences controlling the number of particles and the energy in each system, and then analyze the results obtained when the two systems are put in contact in each situation.

For two bodies A and B: