Force along a contact line, wire/film pull force, or excess pressure inside a bubble/droplet from the Young-Laplace equation.
Fluid Mechanics IICalculation type:
0° = complete wetting. 90° = zero vertical force. 180° = complete non-wetting.
Surface tension force along a contact line:
Young-Laplace pressure (excess pressure inside):
Contact angle interpretation:
| θ range | Wetting behaviour |
|---|---|
| θ = 0° | Complete wetting — surface fully wetted (water on clean glass) |
| 0° < θ < 90° | Partial wetting — hydrophilic surface, capillary rise |
| θ = 90° | Neutral — no net vertical force, flat meniscus |
| 90° < θ < 180° | Partial non-wetting — hydrophobic surface, capillary depression |
| θ = 180° | Complete non-wetting — superhydrophobic surface |
Common surface tension values σ (N/m) at 20°C:
| Fluid pair | σ (N/m) |
|---|---|
| Water / air at 20°C | 0.0728 |
| Water / air at 60°C | 0.0663 |
| Ethanol / air | 0.0223 |
| Mercury / air | 0.487 |
| Glycerin / air | 0.0634 |
| Soap film (approx.) | 0.035 |
| Liquid steel | 1.8 |
Where: