Contact angle in thick capillaries: a derivation based on energy balance

When a solid object is partially dipped beneath the surface of a liquid, this surface loses its horizontal shape near the solid surface and forms a meniscus. This phenomenon is governed by the general trend of any system to minimize its energy. In addition, the equilibrium of forces must be ensured for the meniscus. When both conditions (energy minimization and mechanical equilibrium) are considered together, the relationship between the contact angle and surface tensions (Young's equation) is obtained in a natural and simple way. (letters and comments)