Physics Topics can also be used to explain the behavior of complex systems, such as the stock market or the dynamics of traffic flow.
How did Robert Brown Discovered the Brownian Motion?
Very small, but still visible particles are often present as impurities in a liquid or in a gas. Observations through microscopes show that these particles move in a very random manner in all possible directions. This is known as Brownian motion. This phenomenon can be explained from the concept of molecular motion. Molecules inside a liquid or a gas move randomly in all directions and collide time and again with the small foreign particles (called Brownian particles). These collisions are directly responsible for the Brownian motion.
British scientist, Robert Brown, first observed this continuous and irregular motion of the particles with a powerful microscope. He put some pollen grains in water. These grains, being very light, remained suspended in water. Brown noticed the random, continuous and to and fro motion of these grains. But he was not able to determine the mechanisms that caused this motion. Albert Einstein published a paper in 1905 that explained in precise detail how the motion that Brown had observed was a result of the pollen being moved by individual water molecules. Brownian motion of a particle is shown in Fig. Colloids in a colloidal solution, very small feathers suspended in air, etc., are examples of randomly moving Brownian particles.
Explanation of the origin of Brownian motion: Just after the discovery of Brownian motion, the scientists assumed that the reason of the origin of Brownian motion was chemical reaction, irregular change of temperature, surface tension of liquid, etc. But from various experiments it was proved that these explanations were not correct.
It became possible to explain Brownian motion with the help of kinetic theory. We know that liquid or gas molecules are moving randomly and colliding with floating particles at every instant and from all directions. The force exerted on a floating particle of big size in any direction, due to some colliding molecules, is cancelled by the equal and opposite force due to some other molecules. As a result, the resultant force acting on the floating particle becomes zero and it has no Brownian motion.
But if the floating particle is very tiny in size, the resultant force on it does not become zero as the colliding particles do not exert force equally from all directions. Hence, the floating particle moves along the direction of the resultant force and Brownian motion is observed. As molecular thrusts are random, the magnitude of the resultant force ¡s not equal always. Also, the resultant force does not act always in the same direction. So the floating particle moves in a random manner in all possible directions.
Characteristics of Brownian motion:
- The motion is perpetual, spontaneous, random and continuous. Two Brownian particles, even at close proximity do not have identical motion.
- The motion does not depend on the motion of the container.
- The velocities of the particles increase with rise in temperature.
- Smaller particles have higher average velocities.
- The velocities of the particles become higher in liquids with lower viscosity
- The motion depends only on the mass and the size of the particle and not on the material it is made of.