Key relationship
vt=2r²(ρsphere−ρliquid)g/(9η).
Physics · Practical apparatus
Falling-sphere viscosity
Time a sphere only after it has reached terminal speed. Stokes law applies when Reynolds number is much smaller than one; the readout explicitly flags choices outside that regime.
Open the interactive experiment →Falling-sphere viscosity
முடிவு வேகம் அடைந்த பந்தின் நேரத்தை அளக்கவும். ஸ்டோக்ஸ் விதிக்கு ரெனால்ட்ஸ் எண் ஒன்றைவிட மிகவும் சிறியதாக வேண்டும்.
Key notes, relationships and model limits
Practical tip
Time a sphere only after it has reached terminal speed. Stokes law applies when Reynolds number is much smaller than one; the readout explicitly flags choices outside that regime.
Common trap
Time the sphere after it reaches terminal speed and check low Reynolds number before using Stokes’ law.
Model limits
isolated falling sphere, steady terminal speed, no tube-wall correction. Stokes predictions outside low-Re regime are explicitly flagged; equal densities mean no fall and timing is shown as zero/not measurable.
What you will learn
Adjust falling-sphere viscosity apparatus, observe its reading and derive the indicated physical quantity.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
For r=0.2 mm, density difference 6800 kg/m³ and η=1 Pa s, vt≈0.593 mm/s.
Why this matters
The model connects falling-sphere viscosity with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
In the Stokes regime, doubling sphere radius changes terminal speed by?
- A factor of two.
- A factor of four.
- A factor of one half.
Read the explanation
A factor of four.
Course connection: Virtual apparatus preparation. Check exact board/exam membership in the syllabus sources. Physical practical work remains necessary.