Brownian motion refers to the erratic, random movement of microscopic particles suspended in a fluid, resulting from collisions with the molecules of the surrounding medium. To demonstrate this, a suspension of India ink in water is observed under a microscope. The ink particles, which are small enough to be affected by the thermal motion of water molecules, exhibit constant, jittery movement. This motion is a direct consequence of the kinetic theory of gases, which states that the molecules of a fluid are in continuous, random motion. The random bombardment of ink particles by the water molecules causes them to move in a zigzag pattern, providing visual evidence of molecular activity and the thermal energy of the fluid.