HYDRODYNAMIC PRINCIPLES HYDRODYNAMIC PRINCIPLES هيدرودينامي المبادئ Sekar.L

INTRODUCTION HYDRODYNAMICS & THERMODYNAMICS  Nearly all of the biologic effects of immersion are related to the fundamental principles of HYDRODYNAMICS & THERMODYNAMICS.  It is useful to study the physics of both still & moving water.

DEFINITION:  HYDROMECHANICS / HYDRODYNAMICS is a term used to refer the movement through water.  It is a function of velocity of movement surface area of the moving object & direction of movement of the immersed object.

PROPERTIES & CHARACTERISTICS OF WATER  1. MASS  2. WEIGHT  3. DENSITY  4. SPECIFIC GRAVITY  5. BUOYANCY  6. HYDROSTIC PRESSURE  7. SURFACE TENSION  8. REFRACTION &  9. VISCOSITY

WATER AT REST  DENSITY & SPECIFIC GRAVITY:  Density is defined as MASS per unit VOLUME. كما يتم تعريف الكثافة كتلة لكل وحدة حجم  ρ=m/v, m=mass of the substance v=volume of the substance ρ=(rho)  The density is measured in Kg/m³

ARCHIMEDES PRINCIPLE ARCHIMEDES PRINCIPLE قاعدة أرخميدس a buoyant force equal  It states that when a body is immersed in a fluid it experiences a buoyant force equal to the weight of the fluid which the body has displaced. وهو ينص على أنه عندما يتم غمر جسم في سائل فإنه يواجه قوة الطفو مساوية لوزن السائل الذي أدى الى تشريد الجسم  Each individual part & tissue of the body has its own relative density.  The upper limbs are usually less dense than the lower limbs thus arms float more readily while the legs tend to sink. الأطراف العلوية وعادة ما تكون أقل كثافة من الأطراف السفلية وبالتالي تعويم الأسلحة بسهولة أكبر في حين أن ساقيه تميلالى بالوعة  The relative density of the human body varies with age. (0.87 to 0.97)

SPECIFIC GRAVITY / RELATIVE DENSITY  Specific gravity is the ratio of the density of the substance to the density of the water. الثقل النوعي هو نسبة كثافة المادة إلى كثافة الماء  The specific gravity of water is equal to 1.  Human body is mostly water, the body’s density is slightly less than that of water, with an average specific gravity of (Adolescence & early adulthood)  The specific gravity of a person when there is BONE MASS & MUSCLE MASS. It when there are greater amounts of ADIPOSE TISSUE. الثقل النوعي من الزيادات الشخص عندما يكون هناك زيادة في كتلة العظام والعضلات. أنه يقلل عندما تكون هناك كميات أكبر من الأنسجة الدهنية.  So an human body with low specific gravity of less than 1.0 will float & with high specific gravity of greater than 1.0 will sink.

HYDROSTATIC PRESSURE  PASCALS LAW:  PASCALS LAW: states that the pressure of a liquid is exerted equally on an object at a given depth & the object will experience pressure (Compressive force) that is proportional to the depth of immersion. بالباسكال القانون : تنص على أن ضغط السائل يمارس بالتساوي على كائن على ع مق معين والكائن سوف تواجه الضغط ( القوة الضاغط ة ) الذي يتناسب مع عمق الغم ر  It is the pressure exerted by water on an object immersed in the water. Pressure is defined as force per unit area. P=F/A ومن الضغوط التي تمارس من قبل الماء على جسم مغمورة في الماء. يتم تعريف كقوة ضغط في وحدة المساحة. ف = ف / أ

 The unit of pressure is called a pascal (Pa)  The pressure is measured in newton's per square meter (N/m²)  Fluids have been found experimentally to exert pressure in all directions. تم العثور على السوائل تجريبيا لممارسة الضغط في كل الاتجاهات.  Pressure in a liquid increases with depth & is directly related to the density of the fluid. يرتبط ارتباطا مباشرا في زيادة ضغط السائل مع العمق وإلى كثافة السائل

 Water exerts a pressure of 22.4mmHg/ft of water depth, which translates to 1mm Hg/1.36cm(0.54 in) water depth.  So exercise will be easier to perform closer to the surface of the water where the pressure is less. لذلك سوف يكون من الأسهل ممارسة لأداء أقرب إلى سطح الماء ح يث الضغط أقل  Increase in pressure will reduce EFFUSION, assists VENOUS RETURN, centralizes peripheral blood flow, smoothing out jerky movements & increasing coordination.

BUOYANCY BUOYANCY الطفو  Immersed objects have less apparent weight than the same object on land. الأجسام المغمورة والوزن أقل وضوحا من نفس الكائن على الأرض  Buoyancy, a force opposite to gravity, acts on the object with a force generated by the volume of water displaced. (Archimedes 287 to 212 BC) الطفو، قوة عكس الجاذبية ، ويعمل على كائن مع القوة التي تولدها حجم الماء المزاح. ( أرخميدس 287 حتي 212 قبل الميلاد )

 This is the reason why we float. So the human body with specific gravity of 0.97 will reach floating equilibrium when 97% of his/her volume is immersed. (Weight off-loading) وهذا هو السبب في أننا تطفو. لذا فإن جسم الإنسان مع الثقل النوعي للوصول 0 ، 97 التوازن عائم عند 97 ٪ من حالتهمغمورة هو حجم لها. ( وزن التفريغ )

BUOYANCY CONT BUOYANCY CONT…

 The buoyant force may be therapeutically altered simply through adjustment of the amount of human body immersed. (Partial weight-load; the immersion depth is reduced) قد تكون قوة الطفو تغيير علاجية ببساطة من خلال تعديل كمية من جسم الإنسان مغمورة. ( الجزئي الوزن الحمل، وتنخفضعمق الغمر )  With immersion to the xiphoid – most humans are around 75% off – loaded  With immersion to the umbilicus – around 50%  This weightlessness & joint unloading allows performance of ACTIVE EXERCISES with increased ease.

CENTRE OF BUOYANCY Vs CENTRE OF BALANCE (GRAVITY) - METACENTRE  A body immersed in water is subjected to 2 opposing forces – GRAVITY & BUOYANCY. يتعرض جسم مغمورة في الماء ل 2 القوات المعادية -- الجاذبية والطفو  If these forces are equal & opposite to one another then the body is balanced & no movement takes place. (Floating in equilibrium) وإذا كانت هذه القوات هي على قدم المساواة وعكس بعضها البعض ثم متوازن الجسم والحركة لا تأخذ مكان. ( العائمة في حالة توازن )

 For a human being standing in the anatomical position, the COG is located at the level of the 2 nd sacral vertebra.  The center of buoyancy for human is in the MID-CHEST. مركز الطفو عن الإنسان في منتصف الصدر  The difference between COG (Downward force) & center of buoyance (Upward force) may generate rotational force called torque. ودعا الفرق بين ( قوة الهبوط ) ترس ومركز الطفو ( الت صاعدي القوة ) قد يولد قوة عزم الدوران

REFRACTION  Water presents more resistance to the speed of light.  From the pool edge, a person standing in waist – deep water appear to have foreshortened trunk & legs.  From a pool-edged perspective, monitoring body position of an immersed person requires an understanding of this principle & experience with adjustment for its variance. (Difference between virtual reality of a body part location & its real position)

REFRACTION

SURFACE TENSION  It is defined as the force F per unit length L that acts across any line in a surface & tends to pull the surface open.  ỵ=F/L  The surface of a liquid acts like a membrane under tension.  For example, a drop of water may hang on the end of a straw.

THERMODYNAMICS – SPECIFIC HEAT  All substances on earth is measured in a quantity called a CALORIE.  A calorie is defined as the heat required to raise the temperature of 1 g of water by 1˚C.  1 Calorie is equivalent to 4.18J

 A body immersed in a mass of water becomes a dynamic system.  Water is defined as having a specific heat capacity equal to 1.  Water retains heat 1000 times more than volume of air.

THERMODYNAMICS – THERMAL ENERGY TRANSFER  The therapeutic utility of water depends greatly on both its ability to retain heat & its ability to transfer heat energy.  Exchange of energy in the form of heat occurs in 3 ways:  1. CONDUCTION  2. CONVECTION  3. RADIATION

 Conduction & convection require contact between the exchanging energy sources; radiation does not.  Substances vary widely in their ability to conduct heat.  Water is an efficient conductor of heat.

 In human body the blood becomes a convenient fluid that transfers heat to the surface.  Heat transfer increases as a function of velocity. (So the swimmer loses more heat when swimming rapidly through cold water than a person standing still in the same water.  The transfer of heat to an immersed human body mostly occurring through conduction & convection.

 Heat loss from the body to the surrounding water occurs mostly through radiation & convection.  This thermal conductive property, in combination with its high specific heat, makes water a versatile medium for rehabilitation because it retains heat or cold while delivering it easily to the immersed body part.