Brownian motion is the random, erratic movement of microscopic particles suspended in a fluid (liquid or gas), caused by collisions with the molecules of the surrounding fluid. It is an important phenomenon in physics and chemistry.

1. Observation:

   • Discovered by Robert Brown in 1827 while observing pollen grains in water.

   • Under a microscope, he noticed that the pollen grains moved randomly, even in the absence of external forces like currents or shaking.

2. Cause:

   • The fluid's molecules are in continuous motion due to their thermal energy.

   • These molecules collide with the suspended particles, transferring momentum in random directions.

   • Because the collisions are not uniform or balanced, the suspended particle is "pushed" erratically, leading to zigzag or unpredictable movement.

3. Key Factors Influencing Brownian Motion:

   • Temperature: Higher temperature increases the motion, as fluid molecules move faster with greater energy.

   • Particle Size: Smaller particles exhibit more noticeable Brownian motion because they are easier to move by collisions.

   • Viscosity of Fluid: Higher viscosity reduces the intensity of motion by dampening collisions.

   • Density of the Fluid: More dense fluids cause more frequent collisions, affecting motion.

• Molecules in a fluid are in continuous motion due to thermal energy.

• These molecules collide with the suspended particles, transferring momentum and causing the particles to move in a zigzag pattern.

• The motion is more noticeable in smaller particles because larger particles require more energy to move.

Visualizing Brownian Motion:

Imagine dust particles floating in sunlight. The erratic motion you observe is similar to Brownian motion but occurs on a microscopic scale. Each tiny particle is constantly "hit" by air molecules, causing the random motion.