lecture 1 physical properties.pdf

1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 1 Physical properties of water 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 2 Objectives of this lecture: • To understand the different physical properties of water. • To know how to get benefit of thes...

1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 1 Physical properties of water 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 2 Objectives of this lecture: • To understand the different physical properties of water. • To know how to get benefit of these properties and how to use them to achieve best results in practical applications in hydrotherapy. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 3 Definition: • Hydrotherapy, which is derived from the Greek words hydro and therapeia, meaning “water” and “healing,” is the application of water, for the treatment of physical or psychological dysfunction. • Hydrotherapy can be applied in the form of:  Immersion techniques in water as :  The whole body immersion (total body immersion)  Parts of the body immersion (partial body immersion),  Non immersion techniques as: spraying, bathing or pouring water onto the body. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 4 Physical properties of water: • I- Specific heat and thermal conductivity • II- Buoyancy (upward thrust force) • III- Density • IV- Resistance • V- Viscosity • VI- Surface tension • VII- Hydrostatic pressure 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 5 I-Specific heat and thermal conductivity • Specific heat: is the amount of heat needed to raise the temperature of unit mass by one degree Celsius. ( for example: water takes long time to gain or even lose heat, so it requires great amount of heat/cold to change its temperature, so it is capable of keeping its “hot or cold” temperature for long time before being changed). • Thermal conductivity: the rate at which heat transmitted through a specified material, expressed as the amount of heat that flows per unit time through a unit area. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 6 • The specific heat of water is approximately 4 times that of air, and its thermal conductivity is approximately 25 times that of air. • Thus water retains 4 times as much thermal energy as an equivalent mass of air at the same temperature, and it transfers this thermal energy 25 times faster than air at the same temperature. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 7 Conduction and convection methods of heat transfer • Direct contact with the source of heat will transfer the heat by conduction (example: hot glass of tea).. • while moving fluids will transfer heat by convection (blood stream is the best example for transmission of heat by convection). The rate of heat transfer by convection increases as the rate of fluid flow relative to the body increases, this also explains why we felt warmth when our circulation increases following any physical activity or exercises. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 8 II-Buoyancy force • Buoyancy: is a force experienced as an upward thrust on the body in the opposite direction to the force of gravity. • According to Archimedes’ principle, when a body is entirely or partially immersed in fluid at rest, it is subjected to an upward thrust equal to the weight of the fluid it displaces. • The effect of the buoyancy force increases by increasing the body surface area subjected to it, thus increasing the tendency for this body to float, the peak effect of the upward thrust force on the body is achieved when maximum surface area of the body is subjected to it (the body surface area is horizontal) so that the upward thrust force is perpendicular to it. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 9 Advantages of the buoyancy in exercising: • Submersion decreases stress and compression on weight bearing joints, muscles, and connective tissue (Fig. 2). • It provides support for the weight of the patient’s body during therapeutic activities. • Submersion help to raise weakened body parts against gravity thus providing assistance to the weak muscles when moving from down “beside the body” to the surface of water • It can be also used as source of providing resistance against movement of the limb from the surface of water and moving downward. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 10 Patient exercising in water while wearing foam vest to increase buoyancy (Fig. 2) 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 11 III-Density: • The density of a substance is the relationship between its mass and volume, measured in kg/m3. • Density = mass / volume, kg/m3. Water is most dense at 4°C, expanding at both higher and lower temperatures. Density increases with dissolved substances; hence seawater is denser than pure water. • The relative density of a substance compares the density of a substance using water as a standard. • Densities of various substances are defined by a number value called specific gravity. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 12 • Relative density and specific gravity of an object will depend on the composition of the object and will determine whether an object will float or sink. • If the density of the immersed body is less than the density of the fluid it will float. Conversely, if the density of the immersed body is greater than the density of the fluid, it will sink. • The specific gravity of pure water is 1.0. • If the ratio of an object’s specific gravity to that of water is greater than 1.0; the object will tend to sink; if the ratio is less than 1.0, the body will float. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 13 Pure water versus salt water • Because the density of the human body is less than that of water, having a specific gravity of about 0.974 compared with that of water, it floats in water. • Specific gravity of Pure water is 1 Kg/L. • Specific gravity of salt water is 1.025 Kg/L. • That’s why swimming in salt water is much easier than in fresh water as specific gravity of human body is lesser when compared to salty water than to pure water. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 14 Fig. 1 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 15 IV-Resistance • The water provides resistance to the motion of a body in water. This resistance occurs against the direction of the motion of the body. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 16 Factors affecting the resistance of water: The resistance increases in the following cases: • Speed of the motion of the body. • Speed at which the water moves toward the patient (water jets) • Frontal area of the body parts in contact with the water • Using Paddles or fins (as they increase the frontal area of the body in contact with water. The resistance decreases when: • 1-Keeping the limbs more parallel to the direction of movement. • 2- Decreasing the speed of movement in water. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 17 1/8/2021 Fig. Fig. 3 1 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 18 Fig. 4 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 19 Advantages of water resistance: • Provides safe and effective strengthening and conditioning medium for many patients. • The resistance of water falls to zero when motion stops this provides safety. • The resistance can be increased by increasing the speed of motion or the frontal area in contact with the water, which makes water a very effective environment for training. • The variable resistance and pressure provided by moving water is beneficial for debriding and cleansing wound. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 20 V- Viscosity: • The resistance to movement through water is caused by the friction “coherence” between water molecules. Water acts as a resistance to movement, as the molecules tend to adhere to each other and thus the surface of the body moving through it. • Viscosity of water “coherence between molecules” is greater than that of air, that’s why moving in water is much difficult than that of air. • Viscosity decreases as water temperature increases. This means weaker and smaller muscles move more easily in warmer water. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 21 Vi- Surface tension: • Surface tension is the force exerted between the surface molecules of the fluid. Water molecules have a greater tendency to adhere together at the surface. That’s why an insect can land on the surface of the water. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 22 VII-Hydrostatic pressure • Hydrostatic pressure: is the pressure exerted by a fluid on a body immersed in the fluid. • According to Pascal’s law, a fluid exerts equal pressure on all surfaces of a body at rest at a given depth, and this pressure increases in proportion to the depth of the fluid. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 23 • Because hydrostatic pressure increases as the depth of immersion increases, the amount of pressure exerted on the distal extremities of an upright immersed patient is greater than that exerted on the more proximal or cranial parts of the body. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 24 1/8/2021 Fig. 5 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 25 Benefits of hydrostatic pressure for under water exercising: • Increase in venous return (resulting from increasing hydrostatic pressure on the limbs) may facilitate cardiovascular function. • Assist in promoting circulation or alleviating peripheral edema caused by venous or lymphatic insufficiency. • The support provided by the external pressure may help to brace unstable joints or weak muscles. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 26 Effect of hydrostatic pressure change according to body position in water: • As hydrostatic pressure increases with depth of immersion, the physiological and clinical benefits of the hydrostatic pressure of water will vary with patient positioning in water. • The greatest effects will occur with vertical positioning, in which the feet are immersed deep in the water. • The effects will be much less if the patient is swimming or performing other activities in more horizontal positions close to the water surface, in which the limbs are kept at less depths of immersion. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 27 Effect of hydrostatic pressure according to body position in water: “continued” • There are no hydrostatic pressure effects when non-immersion hydrotherapy techniques are used. (i.e: non immersion techniques doesn’t exerts hydrostatic pressure on body). • So the general effect of non immersion hydrotherapy techniques (which miss the hydrostatic pressure) will be less than the effect of other devices and immersion techniques that exerts pressure on the body parts. 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 28 Thank you 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 29 1/8/2021 Dr wael Osama Aly, Lecturer Basic Science Department, BUC 30