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Terminal velocity in fluids
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Balances weight, buoyancy and viscous drag.
A falling object reaches steady speed when weight = buoyancy + drag; for a small sphere v_t = 2r²(ρ − σ)g/9η.
Dust settling slowly in air.
Larger drops fall faster.
In more detail
A body falling through a fluid reaches terminal velocity when drag and buoyancy together balance its weight. Its acceleration is then zero, and it falls at constant speed.
Real-world uses
- Raindrops reach terminal velocity before reaching the ground.
- Sedimentation in water treatment depends on terminal velocity.
- Engineers designing sediment tanks predict the settling speed of particles in water to remove sand and silt.
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Frequently asked questions
Does size matter?
Yes. Larger or denser objects reach higher terminal velocities.
Can terminal velocity be exceeded?
Only temporarily, for example during a dive or when falling through changing conditions.
Do all particles reach terminal velocity quickly?
Small particles reach it very quickly, while larger objects may take longer to slow to a steady fall speed.
Related topics in Fluids & Elasticity
Viscosity · Poiseuille's equation · Stokes' law · Reynolds number · Surface tension · Surface energy