Cohesion

Definition

Cohesion is the intermolecular force that causes like molecules to stick together, which is particularly significant in liquids. This property is crucial for understanding how fluids behave, including their ability to maintain shape and resist external forces. Cohesion plays a vital role in phenomena such as surface tension, where the cohesive forces at the surface of a liquid create a 'skin' effect, and is also essential in biological systems where it influences processes such as water transport in plants.

5 Must Know Facts For Your Next Test

1. Cohesion is responsible for the formation of droplets, where water molecules stick together due to strong intermolecular forces.
2. In plants, cohesion allows water molecules to travel up through xylem vessels against gravity, contributing to the process of transpiration.
3. The stronger the cohesive forces within a liquid, the higher its surface tension will be, which can affect how insects and other small creatures interact with water surfaces.
4. Cohesion is key in stabilizing the structure of liquids, making them resist changes in shape when subjected to external pressure.
5. In biological systems, cohesion aids in the efficient transport of nutrients and gases within cells and tissues, impacting overall organism health.

Review Questions

• How does cohesion contribute to the unique properties of liquids, particularly in relation to surface tension?
  • Cohesion enhances the unique properties of liquids by allowing like molecules to attract each other strongly. This leads to the formation of surface tension, where molecules at the surface experience a net inward force due to cohesive interactions with other molecules. This effect allows objects that are denser than water, such as certain insects, to 'walk' on water without sinking.
• Discuss how cohesion affects water transport in plants and its significance for plant health.
  • Cohesion is essential for water transport in plants as it enables water molecules to stick together while moving through xylem vessels. This cohesive action facilitates the upward movement of water from roots to leaves against gravitational pull. The efficient transport system maintained by cohesion ensures that plants receive the necessary nutrients and moisture for growth and survival.
• Evaluate the role of cohesion in capillary action and its implications for both natural environments and technological applications.
  • Cohesion plays a crucial role in capillary action by allowing liquid molecules to pull each other along as they move through narrow spaces. This phenomenon is vital in natural environments, such as how water moves through soil and reaches plant roots. In technological applications, understanding cohesion can lead to advancements in fields like fluid dynamics and material science, enabling better design of systems involving liquids, such as inkjet printers and microfluidic devices.

Related terms

Adhesion: The attractive force between different substances or materials, allowing them to stick together.

Surface Tension: The elastic-like force existing at the surface of a liquid, caused by cohesive forces between liquid molecules.

Capillary Action: The ability of a liquid to flow in narrow spaces without the assistance of external forces, primarily due to cohesive and adhesive properties.