Worksheet: Contact Angles

In this worksheet, we will practice relating the contact angles of drops on a surface with the solid–liquid, liquid–gas, and solid–gas surface tensions.

Q1:

How is it possible for a steel needle to be supported on the surface of water?

  • ASinking of the needle is energetically costly because air-water interactions are much weaker than air-steel interactions.
  • BSinking of the needle is energetically costly because it increases the surface area of the water per unit volume.
  • CSteel is less dense than water.
  • DForce must be applied to break hydrogen bonds between surface water molecules.
  • EThe interactions between water molecules are stronger than those between water and steel, so the system has a lower potential energy if the needle does not sink.

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