Properties and Dynamics of Water

Properties of Water

• Water's surface acts like a membrane due to attractions between water molecules.
• Surface tension's attraction is parallel to the surface.
• Resistance due to surface tension changes proportionally to the size of the object moving through the water.
• Moving through water's surface requires more work compared to moving submerged.
• Equipment use at the surface increases resistance.

Hydrodynamics

• Hydrodynamics studies fluids in motion.
• Two types of fluid dynamics: streamline (laminar) and turbulent.
• Streamline flow: Each fluid particle follows a smooth path without crossing others.
• Turbulent flow: Fluid moves erratically in small, whirlpool-like circles (eddies).
• Movement against turbulent water creates more resistance.
• Vigorous movement increases turbulence.
• Water's massaging action is often pleasurable and improves circulation.

Thermodynamics

• Water temperature affects the body in aquatic environments.
• Temperature ranges:
  • Very cold: 1°C - 13°C
  • Cold: 14°C - 18°C
  • Cool: 19°C - 26°C
  • Tepid: 27°C - 32°C
  • Neutral: 33°C - 35°C
  • Warm: 36°C - 37°C
  • Very hot: 41°C - 43°C
• Physiological effects of different temperatures:
  • Very cold/cold: Vasoconstriction, anesthesia
  • Tepid/neutral: No loss of body heat, best for pools.
  • Warm/hot: Vasodilation, analgesia
  • Very hot: Similar to warm, but rapid fatigue and overheating possible.

Specific Heat

• Specific heat is the energy (calories) needed to raise 1 gram of a substance's temperature by 1°C.
• Water has a high specific heat compared to air (4 times higher).
• Water absorbs large amounts of heat energy before getting hot.
• Water absorbs and releases heat energy slowly.
• Hot packs stay hot for more than 30 minutes due to water's high specific heat.

Underwater Exercise

• Water temperature varies based on exercise type.
• Strenuous exercise (like swimming) requires lower temperatures (20-30°C) to help dissipate heat.
• Gentle exercise (50-55 minutes) requires higher temperatures (34°C).
• Water temperature should not exceed 35°C.

Thermal Conductivity

• Thermal conductivity is the rate of heat transfer by conduction.
• Water has high thermal conductivity (25 times greater than air).
• Faster heat transfer occurs with greater temperature difference between the modality and skin.
• Large temperature differences can lead to skin burns.
• Rate of heat transfer is also directly proportional to the contact area and inversely proportional to skin thickness.

Hydrotherapy

• Physiological effects of hydrotherapy depend on:
  • Water temperature
  • Body immersion level
  • Movement state (still or moving)