Question

The contact angle between water and glass is 0°. When water is poured in a glass to the maximum of its capacity, the water surface is convex upward. The angle of contact in such a situation is more than 90°. Explain.

Answer 1

Answer:

Due to the surface tension, the surface of the liquid acts as a stretched membrane. So even if some more water than the rim level of the glass is poured into it, the stretched water surface which holds the glass rim due to adhesion becomes convex upward and the contact angle between the water and the glass becomes more than 90° in this situation. The zero degrees angle of contact for water and the glass is for the situation when the water level is below the rim level of the glass. In some special situations, the angle of contact may change. Read more on Sarthaks.com - https://www.sarthaks.com/313153/the-contact-angle-between-water-and-glass-when-water-poured-glass-the-maximum-the-capacity.

Answer 2

Explanation:

• Because of the surface tension, the liquid surface seems like a stretched membrane.
• So even if a little more water is poured into the glass than the rim point, The stretched surface of that water that retains the glass rim due to adhesion is convex upwards and In this situation, the contact angle between the water and the glass becomes greater than 90 °.  
• The zero degrees contact angle for water and glass is for the situation when the level of water is below the glass rim. In some special situations, the contact angle may change.