Diving Physics Theory

1. Diving Physics Theory

2. We will cover • Pressure • Behaviour of Gases • Vision • Sound • Buoyancy • Heat Loss

3. A column of air rising above one sq. cm. of the Earth’s surface 1 Bar Normal Atmospheric Pressure = 1 Bar = 1 AT = 1 Kg/cm2 Pressure Atmospheric Pressure Results from the weight of this air. It averages at 1013 millibars or approx 1 bar

4. Pressure Deionised Fresh Water at 4° Celsius has 1 bar of pressure for every 10m of water Unless stated in the question, Assume: Sea Water has 1 bar of pressure for every 10m of water

5. Atmospheric and Water Pressure Absolute Pressure is the sum of 1 Bar 2 Bar 10 Metres 1 Bar Pressure

6. Pressure 0 Metres 1 Bar 10 Metres 2 Bar 20 Metres 3 Bar 30 Metres 4 Bar 40 Metres 5 Bar

7. Definitions Mass or Weight Quantity of matter in a body Measured in grammes (g) or kilogrammes (Kg) Pressure Force per unit area acting on a surface Measured in Kgs/cm2, Bar, Atms

8. Definitions Ambient Pressure Local or surrounding pressure Absolute Pressure The total pressure including atmospheric pressure acting on a body, as distinct from gauge pressure which ignores atmospheric pressure

9. Definitions Volume A measure of space occupied Measured in litres (Lts) or cubic centimetres (cc or cm3) Density Mass or weight per unit volume Measured in Kgs/m3, g/cm3

10. Definitions Relative Density Ratio of density of a substance to that of water at 4°C Water = 1, Sea Water = 1.027 Temperature Measured in degrees Kelvin (°K) 273°K = 0°C, 373°K = 100°C 0°K = Absolute Zero

11. Boyle’s Law “At constant temperature, the volume of a given mass of gas varies inversely with the ABSOLUTE pressure”

12. 0 Metres 1 Bar Absolute Pressure x 2 Volume x 1/2 10 Metres 2 Bar Absolute Pressure x 3 Volume x 1/3 20 Metres 3 Bar Absolute Pressure x 4 Volume x 1/4 30 Metres 4 Bar Absolute Boyle’s Law

13. Dalton’s Law In a mixture of gases, each constituent gas exerts a “Partial Pressure” in proportion to it’s percentage of the mixture

14. Dalton’s Law(Example) • Pure Air at 1 Bar Pressure • Air Consists 79% Nitrogen and 21% Oxygen • Partial Pressure (pp) of Nitrogen = 0.79 bar • Partial Pressure (pp) of Oxygen = 0.21 bar

15. Dalton’s Law of Partial Pressure Depth Absolute Metres Pressure ppO2 ppN2 0 1.0 0.21 0.79 10 2.0 0.42 1.58 20 3.0 0.63 2.37 30 4.0 0.84 3.16 40 5.0 1.05 3.95 50 6.0 1.26 4.74

16. Henry’s Law “The amount of gas that dissolves in a liquid is proportional to the partial pressure of the gas in contact with the liquid” (Providing temperature is not changed)

17. Charles’Law “At constant pressure the volume of a gas varies directly as to the absolute temperature” or “At constant volume the pressure of a gas varies directly as to the absolute temperature”

18. P V P V 1 1 2 2 = T T 1 2 Universal Gas Law(Simplification)

19. Vision Underwater • Vision Underwater Affected by: • Refraction • Diffusion • Absorption • Turbidity

20. Refraction • Speed of Light in Air: • 300,000 km / sec • Denser Mediums Slows Light Rays • Bends Light • Snell’s Law

21. Vision Underwater Light Light Air Air Water Water

22. Vision Underwater Fish appears Larger and Closer

23. Diffusion • Water Deflects and Scatters Light • Occurs in All Waters • Reduces Light at Depth • Light at Depth is Dispersed • Reduces Shadows

24. RED ORANGE YELLOW GREEN BLUE VIOLET GREY 5 8 11 19 23 28 31 Colour Absorption DEPTH (metres)

25. Turbidity • Relative Concentration of Suspended Particles • High Concentrations Block Light • Plankton, Stirred up Sediment, Pollution and Run-Off

26. Sound 4 times faster

27. Archimedes Principle “Any object wholly or partially immersed in a liquid experiences an up-thrust (apparent loss of weight) equal to the weight of liquid displaced”

28. Archimedes Principle Compare:- Density of object with density of displaced liquid, to determine state of Buoyancy. Fresh Water Density = 1000kgs/m3 Sea Water Density = 1027kgs/m3

29. Buoyancy - Archimedes Principle Wood Steel WOODSTEEL Volume occupied by block 1000 cm3 1000 cm3 Weight of displaced water 1.0 kgs 1.0 kgs Weight of object 0.7 kgs 5.0 kgs Weight of object in water -0.3 kgs +4.0 kgs

30. Useful Mathematical Formulae “Pi” is approximately equal to 3.14 p

31. Useful Mathematical Formulae Surface area of a block 2[(L x B)+(L x H)+(B x H)] Volume of a block L x B x H H B L

32. Useful Mathematical Formulae Surface area of a circle p R2 Circumference of a circle 2 p R R

33. Useful Mathematical Formulae Surface area of a sphere 4 p R2 Volume of a sphere 4/3 p R3

34. Useful Mathematical Formulae Surface area of a cylinder 2 p RH+2 p R2 Volume of a cylinder p R2H

35. Heat Loss • Diver Suffers Heat Loss through the Following Mechanisms: • Conduction • Convection • Evaporation • Radiation

36. Conduction • Primary Heat Loss Mechanism • Loss of Heat through Direct Contact with Water or Cold Air • Water Removes Heat 25 Times Faster than Air • Cylinder Gas Cold – Cools Lungs

37. Convection • As Water or Air is Heated it Expands and Circulates • Replaced by Cold Water or Air • Moves Heat From Body • Wetsuit Reduces Convection

38. Evaporation • Energy Needed to Change Fluid from Liquid to Gas • Results in Heat Loss • Humidifying Dry Air from Cylinder during Respiration • Evaporation from Diver’s Clothing

39. Radiation • Transfer of Heat • Electromagnetic Waves • Diver Generates Heat Which is Transferred from the Diver • Least Effect of Heat Loss Under Water

40. Summary • Pressure • Behaviour of Gases • Vision • Sound • Buoyancy • Heat Loss