Properties and Dynamics of Water

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Study Notes

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 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.

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 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.

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 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.