<p>Brownian Motion is the random motion of particles in a fluid, as they collide with other atoms or molecules. It is also called <em>pedesis</em>, which is a Greek term for <em>leaping</em>. Many visible, macroscopic particles can be influenced by invisible, microscopic particles, like pollen grains moving by themselves in water.</p>
<p>Brownian Motion is named after Scottish botanist Robert Brown, who described the same in 1827. His work remained unknown till Albert Einstein published a paper in 1905 explaining the discontinuous structure of matter and the existence of atoms and molecules.</p>

Brownian Motion

<p>Diffusion is the movement of particles from higher to lower concentration, and is a kind of Brownian motion. Other factors like increased temperature, an increase in particles or their size, or atmospheric changes can affect the rate of motion.</p>
<p>Some examples include:</p>
<ol>
<li>The Movement of dust motes in a room.</li>
<li>Diffusion of pollutants on the atmosphere.</li>
<li>The movement of holes of electrical charge in semiconductors.</li>
</ol>

Brownian Motion: Diffusion

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Updated July 06, 2019
</div><p dir="ltr">
Brownian motion is the random movement of particles in a fluid due to their collisions with other atoms or molecules. Brownian motion is also known as <em dir="ltr">pedesis</em>, which comes from the Greek word for "leaping." Even though a particle may be large compared to the size of atoms and molecules in the surrounding medium, it can be moved by the impact with many tiny, fast-moving masses. Brownian motion may be considered a macroscopic (visible) picture of a particle influenced by many microscopic random effects.
</p><p>
Brownian motion takes its name from the Scottish botanist Robert Brown, who observed pollen grains moving randomly in water. He described the motion in 1827 but was unable to explain it. While pedesis takes its name from Brown, he was not the first person to describe it. The Roman poet Lucretius describes the motion of dust particles around the year 60 B.C., which he used as evidence of atoms.
</p><p dir="ltr">
The transport phenomenon remained unexplained until 1905 when <a href="https://www.thoughtco.com/who-was-albert-einstein-2698845" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1" dir="ltr">Albert Einstein</a> published a paper that explained the pollen was being moved by the water molecules in the liquid. As with Lucretius, Einstein's&nbsp;explanation served as indirect evidence of the existence of atoms and molecules. At the turn of the 20th century, the existence of such tiny units of matter was only a theory. In 1908, Jean Perrin experimentally verified Einstein's hypothesis, which earned Perrin the 1926 Nobel Prize in Physics "for his work on the discontinuous structure of matter."
</p><p dir="ltr">
The mathematical description of Brownian motion is a relatively simple probability calculation, of importance not just in physics and chemistry, but also to describe other statistical phenomena. The first person to propose a mathematical model for Brownian motion was Thorvald N. Thiele in a paper on the <a href="https://www.thoughtco.com/what-is-a-least-squares-line-3126250" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1" dir="ltr">least squares method</a> that was published in 1880. A modern model is the Wiener process, named in honor of Norbert Wiener, who described the function of a continuous-time stochastic process. Brownian motion is considered a Gaussian process and a Markov process with continuous path occurring over continuous time.
</p><h2 dir="ltr"> <span dir="ltr"> What Is Brownian Motion? </span> </h2><p dir="ltr">
Because the movements of atoms and molecules in a liquid and gas is random, over time, larger particles will disperse evenly throughout the medium. If there are two adjacent regions of matter and region A contains twice as many particles as region B, the probability that a particle will leave region A to enter region B is twice as high as the probability a particle will leave region B to enter A. <a href="https://www.thoughtco.com/definition-of-diffusion-604430" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1" dir="ltr">Diffusion</a>, the movement of particles from a region of higher to lower concentration, can be considered a macroscopic example of Brownian motion.
</p><p dir="ltr">
Any factor that affects the movement of particles in a fluid impacts the rate of Brownian motion. For example, increased temperature, increased number of particles, small particle size, and low <a href="https://www.thoughtco.com/viscosity-2699336" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1" dir="ltr">viscosity</a> increase the rate of motion.
</p><h2 dir="ltr"> <span dir="ltr"> Brownian Motion Examples </span> </h2><p>
Most examples of Brownian motion are transport processes that are affected by larger currents, yet also exhibit pedesis.
</p><p>
Examples include:
</p><UL><LI>The motion of pollen grains on still water</LI><LI>Movement of dust motes in a room (although largely affected by air currents)</LI><LI>Diffusion of pollutants in the air</LI><LI>Diffusion of calcium through bones</LI><LI>Movement of "holes" of electrical charge in semiconductors</LI></UL><h2 dir="ltr"> <span dir="ltr"> Importance of Brownian Motion </span> </h2><p>
The initial importance of defining and describing Brownian motion was that it supported the modern atomic theory.
</p><p>
Today, the mathematical models that describe Brownian motion are used in math, economics, engineering, physics, biology, chemistry, and a host of other disciplines.
</p><h2 dir="ltr"> <span dir="ltr"> Brownian Motion Versus Motility </span> </h2><p dir="ltr">
It can be difficult to distinguish between a movement due to Brownian motion and movement due to other effects. In <a href="https://www.thoughtco.com/biology-meaning-373266" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1" dir="ltr">biology</a>, for example, an observer needs to be able to tell whether a specimen is moving because it is motile (capable of movement on its own, perhaps due to cilia or flagella) or because it is subject to Brownian motion. Usually, it's possible to differentiate between the processes because Brownian motion appears jerky, random, or like a vibration. True motility appears often as a path, or else the motion is twisting or turning in a specific direction. In microbiology, motility can be confirmed if a sample inoculated in a semisolid medium migrates away from a stab line.
</p><h2 dir="ltr"> <span dir="ltr"> Source </span> </h2><p><cite>"Jean Baptiste Perrin — Facts." NobelPrize.org, Nobel Media AB 2019, July 6, 2019.</cite></p><div data-tracking-container="true" dir="ltr">
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Brownian motion is the random movement of particles in a fluid due to their collisions with other atoms or molecules.

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<p dir="ltr">Brownian motion is the random movement of particles in a fluid due to their collisions with other atoms or molecules. Brownian motion is also known as <em dir="ltr">pedesis </em>, which comes from the Greek word for "leaping." Even though a particle may be large compared to the size of atoms and molecules in the surrounding medium, it can be moved by the impact with many tiny, fast-moving masses. Brownian motion may be considered a macroscopic (visible) picture of a particle influenced by many microscopic random effects. </p>

<p>Brownian motion takes its name from the Scottish botanist Robert Brown, who observed pollen grains moving randomly in water. He described the motion in 1827 but was unable to explain it. While pedesis takes its name from Brown, he was not the first person to describe it. The Roman poet Lucretius describes the motion of dust particles around the year 60 B.C., which he used as evidence of atoms. </p>

<p dir="ltr">The transport phenomenon remained unexplained until 1905 when <a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/who-was-albert-einstein-2698845">Albert Einstein </a>published a paper that explained the pollen was being moved by the water molecules in the liquid. As with Lucretius, Einstein's explanation served as indirect evidence of the existence of atoms and molecules. At the turn of the 20th century, the existence of such tiny units of matter was only a theory. In 1908, Jean Perrin experimentally verified Einstein's hypothesis, which earned Perrin the 1926 Nobel Prize in Physics "for his work on the discontinuous structure of matter." </p>

<p dir="ltr">The mathematical description of Brownian motion is a relatively simple probability calculation, of importance not just in physics and chemistry, but also to describe other statistical phenomena. The first person to propose a mathematical model for Brownian motion was Thorvald N. Thiele in a paper on the <a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/what-is-a-least-squares-line-3126250">least squares method </a>that was published in 1880. A modern model is the Wiener process, named in honor of Norbert Wiener, who described the function of a continuous-time stochastic process. Brownian motion is considered a Gaussian process and a Markov process with continuous path occurring over continuous time. </p>

<p dir="ltr">Because the movements of atoms and molecules in a liquid and gas is random, over time, larger particles will disperse evenly throughout the medium. If there are two adjacent regions of matter and region A contains twice as many particles as region B, the probability that a particle will leave region A to enter region B is twice as high as the probability a particle will leave region B to enter A. <a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/definition-of-diffusion-604430">Diffusion </a>, the movement of particles from a region of higher to lower concentration, can be considered a macroscopic example of Brownian motion. </p>

<p dir="ltr">Any factor that affects the movement of particles in a fluid impacts the rate of Brownian motion. For example, increased temperature, increased number of particles, small particle size, and low <a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/viscosity-2699336">viscosity </a>increase the rate of motion. </p>

<p>Most examples of Brownian motion are transport processes that are affected by larger currents, yet also exhibit pedesis. </p>

<ul><li>The motion of pollen grains on still water </li><li>Movement of dust motes in a room (although largely affected by air currents) </li><li>Diffusion of pollutants in the air </li><li>Diffusion of calcium through bones </li><li>Movement of "holes" of electrical charge in semiconductors </li> </ul>

<p>The initial importance of defining and describing Brownian motion was that it supported the modern atomic theory. </p>

<p>Today, the mathematical models that describe Brownian motion are used in math, economics, engineering, physics, biology, chemistry, and a host of other disciplines. </p>

<p dir="ltr">It can be difficult to distinguish between a movement due to Brownian motion and movement due to other effects. In <a data-component="link" data-ordinal="1" data-source="inlineLink" data-type="internalLink" dir="ltr" href="https://www.thoughtco.com/biology-meaning-373266">biology </a>, for example, an observer needs to be able to tell whether a specimen is moving because it is motile (capable of movement on its own, perhaps due to cilia or flagella) or because it is subject to Brownian motion. Usually, it's possible to differentiate between the processes because Brownian motion appears jerky, random, or like a vibration. True motility appears often as a path, or else the motion is twisting or turning in a specific direction. In microbiology, motility can be confirmed if a sample inoculated in a semisolid medium migrates away from a stab line. </p>

<p><cite>"Jean Baptiste Perrin — Facts." NobelPrize.org, Nobel Media AB 2019, July 6, 2019. </cite> </p>

Why Is Random Movement Called Brownian Motion, and What Does It Do?

Brownian Motion

Brownian Motion: Diffusion

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