If you mix ink or paint in water, and then look at this water under a microscope, you can see the rapid movement of the smallest particles of soot or paint in different directions. What provokes such movements?
Who discovered and when
In 1827, the English biologist Robert Brown observed through a microscope a drop of water, which accidentally got a small amount of pollen. He saw that the smallest particles of pollen were dancing, moving chaotically in the liquid. So the Brownian movement named after this scientist was discovered - the movement of the smallest particles dissolved in a liquid or gas. After observing the different types of pollen in his collection, the biologist dissolved the powdered minerals in water.
As a result, Brown was convinced that such chaotic movement was not caused by the liquid itself and not by external influences on the liquid, but directly by the internal movement of the smallest particle. This particle, by analogy with the observed movement, was called the "Brownian particle".
Development of the theory, its followers
Later, Brown's discovery was confirmed, expanded and specified, based on the molecular kinetic theory, by A. Einstein and M. Smoluchowski. And the French physicist Perrin, twenty years later, thanks to the improvement of microscopes in the process of studying the random motion of a Brownian particle, confirmed the existence of molecules proper. Observation of Brownian motion allowed Perrin to calculate the number of molecules in 1 mole of any gas and derive the barometric formula.
The discovery of the movement of a Brownian particle served as proof of the existence of much smaller particles, not even visible in a microscope - molecules of a liquid and any other substance. It is the molecules that, with their constant movement, make particles of pollen, soot or paint move.
Definition and size
If you look at the carcass particles suspended in water through a microscope, you will notice that grains of different sizes behave differently. Relatively voluminous particles, experiencing the same number of shocks from all sides over a certain period of time, do not begin to move. And small particles for the same time interval receive one-sided uncompensated impacts, pushing them to the side, and move.
What is the size of a Brownian particle exposed to molecules? It has been empirically proven that cytoplasmic pollen grains no larger than 3 micrometers (µm), or 10-6 meters, or 10-3millimeter. Larger particles do not become participants in the constant movement discovered by Brown.
So, let's answer the question "what is a Brownian particle". These are the smallest grains of a substance with a size of no more than 3 microns, which are suspended in a liquid or gas, making constant chaotic movement under the influence of the molecules of the medium in which they are located.
Molecular Kinetic Theory
Brownian motion does not stop, does not slow down in time. This explains the concept of molecular kinetic theory, which says that the molecules of any substance are in constant thermal motion. With an increase in the temperature of the medium, the speed of movement of molecules increases, and accordingly, the Brownian particle, which is subjected to molecular impacts, also accelerates.
In addition to the temperature of matter, the speed of Brownian motion also depends on the viscosity of the medium and the size of the suspended particle. The movement will reach its maximum speed when the temperature of the substance surrounding the particle is high, the substance itself will not be viscous, and the dust particles will be the smallest.
Molecules of a substance in which the smallest particles are located, randomly colliding, apply a resultant force (produce a push), causing a change in the direction of pollen movement. But such fluctuations are very short in time, and almost immediately the direction of the applied force changes, which leads to a change in the direction of movement.
The simplest and clearest example that allows you to understand what a Brownian particle is is the movement of dust particles, visible in an oblique sunbeam. In 99-55 years. BC e. the ancient Roman poet Lucretius accurately explained the cause of the erratic movement in the philosophical poem "On the Nature of Things."
Look here: whenever the sunlight comes through
Into our dwellings and darkness cuts through with its rays, Many small bodies in the void, you will see, flickering, Rushing back and forth in a radiant glow of light.
Can you understand from this how tirelessly
The beginning of things in the vast emptiness are restless.
So about great things help to understand
Small things, outlining the path for their comprehension.
Besides, because you need to pay attention
To the turmoil in the bodies flickering in the sunlight
What do you know from it matter and movement, What happens in it secretly and hidden from view.
For you will see there how many dust particles change
The way from the hidden shocks and fly back again, Forever back and forth running in all directions.
Long before the advent of modern magnifying technology, Lucretius, observing an analogue of the movement seen by Brown, came to the conclusion that the smallest particles of matter exist. Brown confirmed this by making one of the most important scientific discoveries.
