Surface tension

Definition

Surface tension is the elastic-like force existing on the surface of a liquid that causes it to behave as if its surface is covered with a stretched elastic membrane. This phenomenon arises due to the cohesive forces between liquid molecules, leading to a minimized surface area and influencing how liquids interact with solid surfaces.

5 Must Know Facts For Your Next Test

1. Surface tension is measured in force per unit length (e.g., dynes/cm or N/m), representing the energy required to increase the surface area of a liquid.
2. A higher surface tension indicates a stronger cohesive force among liquid molecules, which can affect droplet formation and behavior on surfaces.
3. Factors such as temperature and the presence of surfactants can alter surface tension; generally, increasing temperature decreases surface tension.
4. Surface tension plays a crucial role in various applications, including inkjet printing, painting, and the behavior of small organisms on water surfaces.
5. In engineering, understanding surface tension helps predict how fluids will interact with materials, which is vital for processes like coating and lubrication.

Review Questions

• How do cohesion and adhesion relate to surface tension and impact the behavior of liquids on surfaces?
  • Cohesion refers to the attraction between similar molecules within a liquid, contributing to the overall surface tension by keeping the molecules tightly bound together. Adhesion involves the attraction between different substances, such as liquid molecules and solid surfaces. The interplay between these two forces determines how a liquid behaves when it comes into contact with a solid, influencing whether it spreads out (wetting) or forms droplets (beading) based on the balance between cohesive and adhesive forces.
• Discuss how temperature and surfactants can influence surface tension in practical applications.
  • Temperature affects surface tension by altering molecular motion; as temperature rises, molecules move more energetically, which generally reduces cohesion and thus lowers surface tension. Surfactants are compounds that lower surface tension when added to liquids; they disrupt cohesive forces among liquid molecules. Understanding these influences is essential in applications like detergents and paints, where controlling surface tension can enhance spreading or cleaning efficiency.
• Evaluate the significance of surface tension in engineering processes related to fluid behavior on solid surfaces.
  • Surface tension plays a critical role in engineering applications like coatings and lubrication. In these processes, the interaction between fluids and solid materials is governed by surface tension, which affects how fluids spread or adhere. Engineers must consider surface tension when designing systems for painting or applying coatings, as it can determine efficiency and effectiveness. Moreover, controlling surface tension helps optimize lubrication systems by ensuring proper fluid film formation, reducing wear and friction in mechanical components.

Related terms

Cohesion: The attractive forces between similar molecules, which contribute to surface tension by pulling liquid molecules at the surface toward each other.

Adhesion:

The attractive forces between different substances, such as liquid and solid surfaces, which can impact how a liquid spreads or beads on a surface.

Wetting: The ability of a liquid to maintain contact with a solid surface due to intermolecular interactions, significantly influenced by surface tension.