Physics

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Surface Tension Calculator.

Choose a standard surface-tension model: force per length, capillary rise, or droplet pressure.

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Choose a standard surface-tension model: force per length, capillary rise, or droplet pressure.

Use Cases

Engineering fluid systems

Determine capillary rise in tubes or pressure inside droplets for designing microfluidic devices, inkjet printers, or lab-on-chip systems.

Example: Calculate the capillary rise of water in a 0.5 mm radius tube.

Educational physics experiments

Verify surface tension values for liquids in classroom labs by measuring force and contact length, or by observing capillary action.

Example: Find the surface tension of ethanol using a ring tensiometer.

Frequently Asked Questions

How do I calculate surface tension using the γ = F / L model?
Select the 'γ = F / L' model, enter the force (F) in newtons and contact length (L) in meters. The calculator divides force by length to give surface tension in N/m.
What inputs are needed for the capillary rise model?
For capillary rise, select that model and enter surface tension (γ), contact angle, liquid density, gravity, and radius. The calculator computes the rise height using the formula h = (2γ cosθ) / (ρ g r).
How is droplet pressure calculated?
Select the 'Droplet pressure' model, then enter surface tension (γ) and radius. The calculator uses the Young-Laplace equation ΔP = 2γ / r to find the pressure difference across the droplet surface.

Tips & Common Mistakes

Tips

  • Ensure all units match the calculator's defaults: force in N, length in m, density in kg/m³, radius in m, and angle in degrees.
  • For capillary rise, use a contact angle less than 90° for liquids that wet the tube; for non-wetting liquids, the angle is greater than 90° and rise becomes depression.
  • When using the droplet pressure model, remember that the pressure inside a smaller droplet is higher; check your radius input for consistency.
  • If you know the surface tension but need to find force or length, rearrange the formula manually or use the γ = F / L model with known values.

Common Mistakes to Avoid

  • Using degrees for the contact angle in the capillary rise model when the calculator expects radians – always check the unit label.
  • Forgetting to convert density from g/cm³ to kg/m³ (multiply by 1000) before entering it.
  • Mixing up radius and diameter when entering the tube radius for capillary rise or droplet pressure.

Last updated: August 13, 2026