1. Higher Temperature: The most fundamental factor affecting particle speed is temperature. As temperature increases, the average kinetic energy of the particles increases, leading to faster movement.

2. Lower Mass: For a given temperature, lighter particles will move faster than heavier particles. This is because kinetic energy is proportional to both mass and velocity squared.

3. Less Intermolecular Forces: Particles in gases move faster than those in liquids, and particles in liquids move faster than those in solids. This is because intermolecular forces (attractive forces between molecules) are weaker in gases and stronger in solids, restricting movement.

4. Reduced Viscosity: In liquids, viscosity (resistance to flow) can affect particle speed. Lower viscosity allows particles to move more freely.

5. Increased Pressure (for gases): In gases, increased pressure can lead to faster particle movement due to more frequent collisions. However, this is a less significant factor compared to temperature.

Important Note: The above factors mainly describe the average speed of particles. In reality, particles in a substance are constantly moving at different speeds, and their speeds are constantly changing due to collisions.

Let me know if you'd like me to elaborate on any of these points!