Basic Physics Tutorials

Diffusion

If we look carefully, the smoke from the combustion initially can be seen. After a while, smoke cannot be viewed. Have you used a perfume? Even though you spray perfume in the room, other people who are outside the home can also feel the fragrance of the perfume. Likewise, if the mother cooks delicious and appetizing food in the kitchen, the aroma of cooking can be felt from a neighbor’s house. Why is that?

There are many other examples. If you put a few drops of ink into a glass containing clear water, ink, or food coloring will spread evenly throughout the water. This happens automatically. Some previous examples are diffusion events that are often experienced in everyday life. Diffusion is the process of moving substances from a high concentration to a low concentration. What is meant by concentration is the number of molecules/moles of a substance per volume. A high concentration place is a place where there are many molecules of substances per volume. Conversely, low concentrations are places where there are few molecules per volume.

Internal energy of an ideal gas

Energy in a monatomic ideal gas

The energy in the monatomic ideal gas is the total amount of translational kinetic energy of monatomic ideal gas molecules. The total amount of translational kinetic energy of the ideal gas molecules = the product of the average translational kinetic energy of each molecule and the number of molecules (N). Mathematically:

Theorem of equipartition of energy

The energy equipartition theorem was derived theoretically by Clerk Maxwell using statistical mechanics. It is called a theorem because there is no proof through experimentation. The energy partition means equal distribution of energy.

KE = average translational kinetic energy of gas molecules (Joule)

k = Boltzmann’s constant = 1.38 x 10^-23 J/K

T = absolute temperature of the ideal gas molecule (Kelvin)

Average kinetic energy of gases

In addition to pressure, one of the quantities that states the macroscopic nature of gas is temperature (T). Gas pressure equation:

Average kinetic energy of gases 1

Kinetic theory of gases

The kinetic theory states that every substance consists of atoms or molecules and that the atom or molecule moves continuously carelessly. This assumption of kinetic theory matches the situation and condition of the atom or molecule of the gas constituent. The force of attraction between the atoms or molecules making up the gas is feeble so that atoms or molecules can move freely.

Boyles law Charless law Gay-Lussacs law

Article Boyle’s law, Charles’s law, Gay-Lussac’s law

Boyle’s law

Robert Boyle (1627-1691) conducted experiments to investigate the quantitative relationship between gas pressure and volume. This experiment is carried out by inserting a certain amount of gas into a closed container. Until a pretty good approach, he found that if the gas temperature was kept constant, then when the gas pressure increased, the gas volume was reduced. Likewise, when the gas pressure decreases, the gas volume increases. Gas pressure is inversely proportional to gas volume. This relationship is known as Boyle’s Law. Mathematically:

The ideal gas law

The gas laws of Boyle, Charles law and Gay-Lussac do not apply to all gas conditions, so our analysis becomes more difficult. Therefore, presented the ideal gas model. Ideal gas does not exist in everyday life; the ideal gas is the just perfect form to facilitate analysis. The existence of this ideal gas concept also really helps us in reviewing the relationship between the three laws of gas.

The relationship among temperature, volume, and gas pressure

By referring to the three gas laws above, we can derive a more general relationship between temperature, volume, and gas pressure.

Entropy

The specific statements of the second law of thermodynamics can’t describe for all irreversible processes, so we need a general statement. This general statement is expected to explain all irreversible processes occurring in the universe. The general statement of the second law of thermodynamics was formulated in the mid-nineteenth century, through a quantity called entropy (S). Entropy was first introduced by Clausius and was formulated from the Carnot cycle (perfect caloric engine). According to Clausius, entropy changes are experienced by a system, when the system gets additional heat (Q) at a constant temperature, which is represented by the equation:

Coefficient of performance of the cooling machine

Article about Coefficient of performance of the cooling machine

A cooling machine is a machine that takes heat from a low-temperature place, then transfers it to a high-temperature area. For this process to happen, the machine must do the work because the heat naturally flows from high temperature to low temperature. This is by Clausius’s statement:

It is impossible for a cooling machine to transfer heat from a low-temperature place to a high-temperature place, without work (Second law of thermodynamics—Clausius statement).

The machine works (W) to transfer heat, from low temperature (Q_L) to high temperature (Q_H). Based on conservation of energy, Q_L + W = Q_H.

Carnot heat engine and carnot cycle

To find out how to increase the efficiency of the heat engine, a French scientist named Sadi Carnot (1796-1832) examined an ideal theoretical caloric machine in 1824. At that time, the first law of thermodynamics had not been formulated, nor the second law of thermodynamics. The first law has not been formulated because scientists do not yet know that heat is energy. After Joule and his colleagues experimented in the 1830s, scientists discovered heat is energy that moves due to temperature differences. So, the first law of thermodynamics was formulated after 1830. Sadi Carnot had been researching the theoretical ideal caloric engine in 1824. His research was actually to increase the efficiency of the steam engine. Most steam engines of that time were less efficient.