In gravity settling, heavier particles settle at what rate compared to lighter particles?

• A. Slower
• B. Unpredictable
• C. Faster
• D. The same

Answer: (C)

In gravity settling, how fast a particle settles comes from the balance of forces: weight pulling downward, buoyancy pushing upward, and drag resisting motion. The driving force for settling is the difference between the particle’s weight and the buoyant force, which scales with how much denser the particle is than the surrounding fluid. Heavier particles have a larger density difference, so for the same size and shape they experience a stronger downward pull. That larger net force leads to a higher terminal velocity—the point where drag exactly balances gravity—so they settle faster. The math for small, laminar particles shows terminal velocity increasing with (ρ_p − ρ_f) and with d^2, meaning denser particles settle quicker under gravity. In practice, while size also affects rate, the density difference is the key reason heavier solids settle faster than lighter ones.