Definitions THE MOLECULAR MODEL OF MATTER: The essential defining characteristics of the Molecular Model are: (a) Matter consists of tiny particles called molecules. (b) Each different kind of matter consists of a different kind of molecule. (c) the molecules in matter are in constant motion. (d) Molecules move and interact in accord with the laws of motion, the laws of force, and the laws of conservation applicable to motion. BROWNIAN MOTION: The constant, irregular motion of very fine particles (such as fine dust or smoke) suspended in a fluid and observed with a microscope. Brownian Motion is taken as evidence for molecules, which collide with the observed particles and cause the jittery motion.

The animation shows a large disk that represents a particle of fine dust or smoke viewed through a microscope. Observe the jittery motion which is called Brownian Motion. If you click twice on the dust particle, then press the space bar on the keyboard, the molecules will become 'visible.' But, remember, molecules are very small and remain forever invisible to the naked eye.

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