NCERT Exercise 9.2 - Mechanical Properties of Fluids
Question: Explain why (a) mercury-glass contact angle is obtuse but water-glass is acute, (b) water spreads on glass but mercury forms drops, (c) surface tension is independent of area, (d) detergent water has small contact angle, (e) a free liquid drop is spherical.
Answer: Explanations based on **intermolecular forces and surface energy minimisation**.
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