It's important to clarify what kind of "size" we're talking about because the relationship between size and speed of particles depends heavily on the context:

1. Size of a Particle:

* Individual Particles: The size of an individual particle doesn't directly influence its speed. For example, a small dust particle and a large raindrop can both travel at the same speed. The speed is more dependent on external forces like gravity, wind, or collisions.

2. Size of a System:

* Gases and Liquids: In gases and liquids, the speed of particles is related to temperature. Higher temperatures mean higher average kinetic energy, and thus faster moving particles. However, the size of the system (e.g., a larger container of gas) doesn't directly influence the speed of individual particles.

* Solids: In solids, particles are tightly packed and vibrate around fixed positions. The size of the solid affects the overall vibration amplitude, but not necessarily the speed of individual particle vibrations.

3. Collisions:

* Larger particles in collisions tend to have a lower speed after the collision than smaller particles because they carry more inertia. However, they can impart a larger impulse (force over time) to smaller particles, potentially increasing the speed of the smaller particles.

In Summary:

There is no simple, universal answer to how the speed of particles changes with size. It depends heavily on the specific situation and the type of particles involved. In most cases, the speed of individual particles is more influenced by factors like temperature, collisions, and external forces rather than their size.