There isn't a single law specifically stating that all matter is made of small particles in motion. This concept is actually a fundamental principle derived from multiple areas of physics and chemistry.

Here's how we can break it down:

* The Kinetic Molecular Theory: This theory is a foundational concept in chemistry that explains the behavior of gases, liquids, and solids. It states that matter is composed of particles (atoms and molecules) in constant random motion. The higher the temperature, the faster the particles move.

* Atomic Theory: The atomic theory, developed by John Dalton and later refined, states that all matter is made up of atoms, the smallest unit of an element. These atoms are in constant motion.

* Quantum Mechanics: At the quantum level, the behavior of particles is governed by quantum mechanics. While the particles are not always moving in the classical sense, they possess energy and are constantly interacting with other particles.

So, while there isn't a single law named after this concept, it is a core idea supported by various scientific theories and models.