Liquids exhibit fascinating behaviors due to cohesive and adhesive forces. These molecular attractions create surface tension, allowing water striders to walk on ponds and raindrops to form. They also enable capillary action, which helps plants transport water and makes paper towels absorbent.

Understanding these liquid properties is crucial in physics and has wide-ranging applications. From designing better ink pens to developing microfluidic devices for medical diagnostics, cohesion and adhesion in liquids play a vital role in our daily lives and technological advancements.

Cohesion and Adhesion in Liquids

Cohesive vs adhesive forces

• Cohesive forces attract molecules of the same substance hold liquid molecules together (water molecules in a drop)
• Stronger cohesive forces create higher surface tension liquids bead up on surfaces
• Adhesive forces attract molecules of different substances occur between liquid and container molecules (water adhering to glass)
• Adhesive forces cause liquids to wet surfaces spread out on contact
• Intermolecular forces play a crucial role in determining the strength of cohesive and adhesive forces

Surface tension in liquids

• Property of liquids caused by cohesive forces molecules at surface experience unbalanced forces
• Acts like an elastic membrane minimizes liquid's surface area (water strider walking on pond)
• Allows formation of droplets (rain) and bubbles (soap)
• Enables floating of denser objects (paperclip on water surface)
• Affected by temperature higher temperatures reduce surface tension
• Impurities like surfactants (dish soap) can lower surface tension
• Interfacial tension occurs at the boundary between two immiscible liquids

Capillary action and applications

• Ability of liquid to flow through narrow spaces without external forces (water rising in a straw)
• Occurs when adhesive forces between liquid and surface exceed cohesive forces within liquid
• Liquid drawn upwards against gravity narrower spaces enable higher rise
• Height of liquid column determined by: $h = \frac{2\gamma \cos\theta}{\rho gr}$
  1. $\gamma$: surface tension
  2. $\theta$: contact angle
  3. $\rho$: liquid density
  4. $g$: acceleration due to gravity
  5. $r$: radius of the tube
• Jurin's law describes the relationship between capillary rise and tube radius
• Enables water transport in plants through xylem vessels (trees)
• Absorption of water by soil and roots (crops)
• Wicking in fabrics (towels) and paper (paper towels)
• Ink flow in pens (fountain pens) and printing (inkjet)
• Microfluidic devices for chemical analysis (lab-on-a-chip) and medical diagnostics (blood tests)

Fluid properties and behavior

• Viscosity measures a fluid's resistance to flow and deformation
• Fluid dynamics studies the motion of liquids and gases under various forces
• These properties influence capillary action and surface tension phenomena