Apnée Cours S2 2017 Physics PDF

# Manuel Niveau S2 Physique ## Commission Apnée This course is a work of LIFRAS (asbl). Any partial or total reproduction is strictly forbidden. # Niveau S2 Physique ## Plan du Cours ### 2. La Physique #### 2.1 Les Grandeurs Fondamentales - **Masse M** - A mass is a quantity of matter....

# Manuel Niveau S2 Physique ## Commission Apnée This course is a work of LIFRAS (asbl). Any partial or total reproduction is strictly forbidden. # Niveau S2 Physique ## Plan du Cours ### 2. La Physique #### 2.1 Les Grandeurs Fondamentales - **Masse M** - A mass is a quantity of matter. - Official unit of measurement: the kilogram (kg). - **Force F** - A force is "something" capable of putting a mass in motion. - Official unit of measurement: the Newton (N). - **Weight P** - The weight of a body is the force that attracts that body towards the center of the earth. - Official unit of measurement: the Newton. - Relationship between P and M: P = M x 9,81 (approximately 10). - **Confusion** - Assimilation between weight and mass, hence the improper use of the kilogram to measure weight. - **Capacity and Volume** - 1 dm³ = 1 liter. - 1 m³ = 1000 dm³ = 1000 liters. - **Density p** - Volumetric density is the mass of a body relative to its volume. - Official unit of measurement: the kg per m³ (kg/m³). #### 2.2 La Pression ##### 2.2.1 Definition - A pressure is a force exerted on a surface. - P = F/S - Official Unit: The Pascal (Pa). - The Pascal is the pressure exerted by a force of 1N over a surface of 1 m². - Other practical unit: - The bar = 1 kg/cm². - 1 bar = ± 100 000 Pa. #### 2.3 Les Différents Types de Pression ##### 2.3.1 La Pression Atmosphérique - Atmospheric pressure is the pressure due to the weight of the air above us. - It therefore decreases with altitude. - At sea level, it is worth: - 1 atm = 1013 hPa = 1,013 bar = 760 mm of mercury. - Sufficient approximation: 1 atm = 1 bar. ##### 2.3.2 La Pression Hydrostatic - Hydrostatic pressure is the pressure due to the weight of a stationary column of water. - It therefore increases with depth. - It is worth approximately 1 bar for every 10 meters of water. ##### 2.3.3 La Pression Relative - Relative pressure is the pressure measured relative to a reference pressure. - This pressure is relative to atmospheric pressure. ##### 2.3.4 La Pression Absolute - Absolute pressure is the total pressure that we actually undergo. - In diving, this is the sum of atmospheric pressure and hydrostatic pressure. - Pabs = Patm + Phyd #### 2.4 Le Milieu du plongeur : L'eau et L'air ##### 2.4.1 L'Air - Air is a mixture of gases. - Approximation: 80% N2 and 20% O2. - Air has a volumetric density of approximately 1,25 kg/m³. ##### 2.4.2 L'Eau - **Volumetric Density** - The volumetric density of freshwater is 1000 kg/m³ (at 4 °C). - The volumetric density of seawater is approximately 1033 kg/m³. - **Thermal conductivity** - Water is much more conductive to heat than air. - **Consequences** - Significant cooling in water. - Necessary combination. - **Thermocline** - Zone of thermal transition between surface waters and deep waters. - **Halocline** - Caused by a strong salinity gradient affecting the density of seawater. - In concert with the thermocline. - Found when there is freshwater and saltwater in the same environment. - **Consequences** - Temperature difference. - Water turbidity, reducing visibility over a few meters. - Can be an ecological barrier for fauna and flora (Ecotone). ##### 2.4.3 L'Eau - L'Air - **Propagation of sound** - Sound is a wave that needs a medium to propagate. - The denser the sound, the faster the sound wave travels. - **Consequences** - Sound travels faster in water than in air. - In water, it is impossible to determine the direction of sound. #### 2.5 Les lois physiques relatives à la lumière ##### 2.5.1 Quatre Phénomènes - Light is a wave that can propagate even in a vacuum. - The denser the transparent medium, the slower the light wave propagates. - Light entering water undergoes four phenomena: - Reflection. - Refraction. - Diffusion. - Absorption. ##### 2.5.2 La Réflexion - Reflection is the return of part of the light to the first medium. - This is the "mirror" effect. ##### 2.5.3 La Réfraction - Refraction is the change in direction of the part of the light that enters the second medium. - This is the "broken stick" effect. ##### 2.5.4 Conséquences Pour la Plongée - **Consequences of refraction:** - **Impression of rapprochement** - Apparent distance = 3/4 of the actual distance. - **Impression of magnification** - Apparent size = 4/3 of the actual size. ##### 2.5.5 La Diffusion - Diffusion is the deviation of light in all directions by particles suspended in water. - This is the "fog" effect. ##### 2.5.6 L'Absorption - Absorption is the loss of light intensity and colors with depth. #### 2.6 Le Principe de Pascal ##### 2.6.1 Définition - The pressure exerted on a fluid is transmitted by it and integrally in all directions. #### 2.7 Le Principe d'Archimède ##### 2.7.1 Définition - Any body immersed in a fluid undergoes an upward vertical thrust equal to the weight of the volume of fluid it displaces. ##### 2.7.2 Expérience - The apparent weight of a body is calculated by the difference between the real weight of the body and the Archimedes thrust. ##### 2.7.3 Flottabilité - **Positive**: The Archimedes thrust is greater than the real weight. - The body rises. - **Null**: The Archimedes thrust is equal to the real weight. - The body is in equilibrium. - **Negative**: The Archimedes thrust is less than the real weight. - The body sinks. - It depends on two parameters: - Weight of the body. - Volume of the body. ##### 2.7.4 Applications á la Plongée - Lung-ballast. - Combination. - Ballast. - The snorkel (Surface breathing) - Duck dive #### 2.8 Loi de Boyle-Mariotte ##### 2.8.1 Définition - At constant temperature, the volume of a gas is inversely proportional to the absolute pressure it experiences. ##### 2.8.2 Effet á la Descente - The pressure increases with depth. - The volume of the air in the lungs decreases. ##### 2.8.3 Effet á la Montée - The pressure decreases with depth. - The volume of the air in the lungs increases. ##### 2.8.4 Conséquences Pour le Corps - **Pressure variation:** - Use of the snorkel up to 0.40m maximum. - Ear equalization and barotrauma. - Variation in the impact of weight. - **Reduction of air volume in the lungs:** - A feeling of chest compression. - A feeling of shortness of breath. - **Bloodshift** - **Effects on gases in the body (Dalton's Law):** - Feeling of well-being when descending. - Syncope risk at 7m during ascent. #### 2.9 Loi de Dalton : La Pression Partielle ##### 2.9.1 Définition - At constant temperature, the absolute pressure of a mixture of gases is equal to the sum of the partial pressures of each of the constituent gases. ##### 2.9.2 Applications - **Toxicity of gases:** Biochemical accidents. - **Syncope risk at 7m**. - **Samba**. - **Decompression accidents**. #### 2.10 Loi de Henry ##### 2.10.1 Définition - At constant temperature and saturation, the quantity of a gas dissolved in a given liquid is directly proportional to the pressure exerted by the gas at the surface of the liquid. ##### 2.10.2 Applications - Decompression accidents. - Diving computers. ## Credits Photos - Photo Grotte Contre-jour: Frédric Willem - Photo Apnéiste compensant: Frédric Willem - Photo Apnéiste descendant: Frédric Willem ## Illustrations - Manuel Lifras ## Realisation - Philippe Cotton MF1070 - S4-AI ## Bibliographie - Manuel Lifras 2012