Properties Of Water PDF

PROPERTIES OF WATER Presented By Dr. Mai Abo Elhamd, PhD, Cairo University 4- Surface tension Definition: The surface of a fluid acts as a membrane under tension due to the attraction forces between water molecules and each other Properties: The attraction of surface molecules is parallel to the...

PROPERTIES OF WATER Presented By Dr. Mai Abo Elhamd, PhD, Cairo University 4- Surface tension Definition: The surface of a fluid acts as a membrane under tension due to the attraction forces between water molecules and each other Properties: The attraction of surface molecules is parallel to the surface.  The resistive force of surface tension changes proportionally to the size of the object moving through the fluid surface. Clinical Significance: An extremity that moves through the surface performs more work than if kept under water.  Using equipment at the surface of the water increases the resistance.  5- hydrodynamics Definition: Hydrodynamics comprise the physical properties and characteristics of fluid in motion. Properties: hydrodynamics includes two types of fluid dynamics: streamline (or laminar flow) and turbulent flow. Streamline flow occurs when each particle of the fluid follows a smooth path without crossover of paths. Turbulent flow is the flow of fluids in erratic, small, whirlpool-like circles called eddy currents or eddies.  Clinical Significance:  Movement against turbulent water will encounter more resistance, as experienced while moving a body part in a whirlpool when the water is agitated.  The more vigorous the movement (and the more people moving), the greater the turbulence created.  The massaging action of the water on the skin is pleasurable for most people. It enhances circulation, improves venous return, and reduces pain. 6- thermodynamics Water temperature has an effect on the body and therefore in the aquatic environment. Water temperature Degree Very cold 1 C⁰ - 13 C⁰ Cold 14 C⁰- 18 C⁰ Cool 19 C⁰- 26 C⁰ Tepid 27 C⁰ - 32 C⁰ Neutral 33 C⁰- 35 C⁰ Warm 36 C⁰ - 37 C⁰ Very hot 41 C⁰ - 43 C⁰ Expected physiologic effect of water temperature: Very cold, cold, Vasoconstriction, anesthesia cool Tepid and neutral No loss of body heat or change in core temperature or limb size (best temperature range for pool ex.) Warm and hot Vasodilatation , analgesia Very hot Same as warm and hot temperature but may cause rapid fatigue and overheating 7-Specific heat Definition: is the amount of (calories) required to raise the temperature of 1 gram of substance by 1C. Properties: Water has a high specific heat index as compared to air, i.e. it is 4 times as that of air. This means that: water can absorb large amount of heat energy before it begins to get hot. it also means that water absorbs and releases heat energy slowly. Clinical significance: It can store heat for long time, i.e. the hot packs can remain hot for more than 30 min. It releases heat on the skin very slowly. Hot applications are used to improve circulation and reduce ms spasm and tension.  In underwater exercise, water temperature is different according to mode of exercise.  20- 30 ⁰C for strenuous exercise such as swimming to help dissipate heat generated by the body during the exercise.  34 ⁰C for gentle exercise which last for 50-55 min.  Water temperature should not exceed 35⁰C. 8- Thermal conductivity Definition: Thermal conductivity is the rate of heat transfer by a substance through conduction. Properties.  Water has high thermal conductivity as compared to air, i.e., it is 25 times as that of air. Rate of heat transfer is directly proportional to the thermal conductivity of the material, so:  The greater the temperature difference between the heating modality and the skin, the faster the rate of heat transfer to the skin and vice versa.  If the temperature difference is very large, the rate of heat transfer may be very fast and may cause skin burn. Directly proportional to the area of contact between the heating modality and skin, so; Larger contact area, i.e., the back, has faster heat conduction that smaller contact area, i.e., hand or ankle. Inversely proportional to skin thickness, so; Skin is heated very rapidly, while deeper tissues require longer time to heat up The physiological effects of hydrotherapy primarily depend upon:  The temperature of the water,  How much of the body is immersed in the water, and  Whether the person or body part in the water is at rest or moving. Thank you