There are several activities that can provide evidence for the fact that matter is composed of particles. Here are two commonly used activities that demonstrate the particulate nature of matter:
Brownian motion: The observation of Brownian motion is a classic experiment that provides evidence for the existence of particles in matter. In this experiment, tiny particles suspended in a fluid (e.g., smoke particles in air or pollen grains in water) exhibit random, erratic motion. This motion is caused by the continuous collisions of the particles with the molecules of the surrounding medium. By observing this motion under a microscope, it becomes evident that matter is composed of discrete, individual particles.
Diffusion: Diffusion is the process by which particles spread out and mix with one another due to their random motion. When a drop of colored dye is added to a glass of water, for example, the dye molecules disperse and eventually become evenly distributed throughout the water. This phenomenon can be observed in various contexts, such as the spreading of odor in a room or the mixing of gases. The observation of diffusion provides evidence for the existence of individual particles that move independently and spread out to occupy available space.
Both the Brownian motion and diffusion experiments support the particle theory of matter and demonstrate that matter is composed of discrete entities that interact and move independently.