Practise Edexcel IAL Physics 1.2.3 by applying Stokes’ law to drag and terminal velocity and predicting viscosity and temperature effects.
A student determined the viscosity of a liquid using the falling-ball method.
When falling through the liquid, the ball reached terminal velocity.
The flow of liquid around the ball was laminar.
Calculate the viscosity of the liquid.
terminal velocity of ball =5.4×10−4 m s−1
radius of ball =0.50×10−2 m
drag force =1.1×10−2 N
Viscosity of liquid =
Use F = 6πηrv.
η = 2.2 × 10² Pa s.
Example: 1.1 × 10⁻² N = 6π × η × 0.50 × 10⁻² m × 5.4 × 10⁻⁴ m s⁻¹, so η = (1.1 × 10⁻²)/(6π × 2.7 × 10⁻⁶) = 216 Pa s.