The stiffness of water on a frozen lake is primarily due to which property?

• A. Surface tension
• B. Viscosity
• C. Density
• D. Temperature

Answer: (A)

Surface tension is the restoring force that resists deformation of the air–water interface. It acts like a tiny skin on the surface, so small dents or waves require work to stretch and bend that boundary. On a frozen lake, this interfacial force makes the surface appear and behave stiffer than the bulk liquid because any disturbance at the surface has to overcome the cohesive forces pulling surface molecules together. Viscosity damps motion but doesn’t provide the main resistance to surface deformation; density relates to mass and buoyancy rather than surface stiffness; temperature affects how strong surface tension is, but the underlying property that gives the surface its stiffness is the surface tension itself.