To answer the question, what is the internal energy, let us remember the example that led the school teacher, explaining the meaning of the kinetic and potential energies.In simple terms, the first of them - is the energy of motion that has any moving body, and the second - unrealized ability to perform any work.Moreover, these two energies are able to "flow" into one another.
Let's use an example.On the plastic surface (lead sheet) is a heavy metal ball.Take it and climb to the height of the arm.As he moved to the top of the point, its kinetic energy decreases, and the potential to increase, reaching its peak at the time of the stop.But we let go of the ball, and he was under the influence of gravity swoops.What happens at this point?Very simple: potential (stored) energy is transformed into an accelerated motion.This happens as long as the ball drops on the surface and stops (this is why in the example we have a plastic base).At first glance it may seem that the energy of the ball disappeared, but it is not, as the internal energy has increased.If you carefully examine the crash site, and there is visible dent in the metal, and the ball was deformed (especially if he is also the lead).Moreover, the point of contact heat has been evolved.
What happens at the molecular level in the metal structure?The molecules that make up the material, combined with each other by the mutual attraction and repulsion.The deformation causes the displacement of some of them, bringing the total internal energy change.These particles are invisible to the eye but also have the kinetic and potential energies.The offsets in the internal structure of the fall reported additional energy molecules.The internal energy due to the interaction of the particles, so there is always.This is one of the characteristics of matter.Internal energy - is the sum of kinetic and potential inherent in all the atoms and molecules of the body.
There is a formula for calculating.An important point - this method is suitable only for the calculation of an ideal gas.In it the potential energy
F = (I / 2) * (m / M) * T * R,
where I - the coefficient of degrees of freedom.This takes into account only the number of molecules m, and the ambient temperature T. In real atmospheres need to provide for an additional occupied volume, pressure, and the structure of the molecules themselves.
Speaking of mutual forms of energy conversion can not fail to point Y. R. Mayer.As the ship's doctor, he drew attention to the difference between the intensity of the colors of the blood of the sailors and the inhabitants of cold countries.Subsequently, it was he who pointed to one of the main characteristics of energy - its permanence.It does not disappear, and only converted to other species, the sum value remains unchanged.
internal energy of the water is also subject to the general laws.For example, the sailors are well aware that after the last storm water temperature outside the ship always higher than before.This is due to the fact that the atmospheric front informed of their energy body of water, heating it.Another example to which every person faces every day - it is boiling.Enough to put a container of water on the stove and turn on the gas, the internal energy of the fluid begins to rise.The molecules get extra boost their speed increases.Accordingly, the number of mutual collisions also becomes larger.But if you remove the source of the outside temperature, the water has cooled down immediately.This is due to the motion of the particles accumulated in the internal energy.By the way, the process of cooling is also a manifestation of the law of conservation: the ambient air is heated and expands, making the work.