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.
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.