Particle behavior refers to how tiny particles, such as atoms and molecules, move and interact with one another. These particles are in constant motion, and their speed and arrangement can change based on temperature and pressure. For example, in a solid, particles are closely packed and vibrate in place, while in a gas, they move freely and spread out. The behavior of particles is influenced by forces like gravity, electromagnetism, and nuclear forces. Understanding these interactions helps explain various phenomena, such as chemical reactions and phase changes, where substances transition between solid, liquid, and gas states.