Associate Safety Professional Practice Exam 2025 - Free Practice Questions and Study Guide

The settling rate of particles in the air is influenced largely by their density. Lead oxide particles have a significantly higher density compared to silica particles. When particles are suspended in the air, the force of gravity acts on them; denser particles experience a greater gravitational pull which causes them to settle more quickly than lighter particles. This principle is anchored in Stokes' Law, which describes the motion of spherical particles in a fluid medium, indicating that the terminal velocity of falling particles is proportional to their density. Therefore, the primary reason for the quicker settling of lead oxide particles is their higher density compared to silica.

While chemical composition, heating methods, and moisture content can affect the behavior and characteristics of particles, the fundamental factor determining the rate of settling in this context is the difference in density between the two materials.