Diving Physics

# Diving Physics

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## Diving Physics

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1. Diving Physics

2. Diving Physics • Buoyancy • Pressure • The Gas Laws • Light • Sound • Heat

3. Buoyancy • Archimedes Principle • "Any object wholly or partly immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object." • Float (positive buoyancy) • Neutral • Sink (negative buoyancy) • Displacement vs. density • Weight of fresh water (62.4 lbs./cu.ft.) • Weight of salt water (64 lbs./cu.ft.)

4. Buoyancy • Human factors affecting buoyancy: • Fat • Muscle • Bone • Equipment factors affecting buoyancy

5. Buoyancy • Controlling buoyancy: • BCD • Natural lung capacity • Exposure suits • weight systems • relaxation

6. Buoyancy Displacement Float or Sink? • Object weighs 128 lbs, • Displaces 2 cu ft • Sink or Float? • Archimedes Principle • Volume-Weight • Relationship • 1 cu ft Sea Water = 64 lbs • (Fresh Water = 62.4 lbs) • Object weighs 128 lbs, • Displaces 1 cu ft • Sink or Float? Body Position • Object weighs 128 lbs, • Displaces 4 cu ft • Sink or Float? Neutral Float Sink Level Head Down Head Up Diver weighs 170 lbs and requires 22 lbs weight for neutral buoyancy in sea water. What is the diver’s volume? • Buoyancy Controlled by BCD/Weight • Buoyancy May Change with Depth

7. Pressure • Defined as a force per unit area • In US measured as pounds per square inch (psi) • Atmospheric pressure: • Pressure of 1 sq in of atmosphere (14.7 psi) • Hydrostatic pressure • Pressure due to weight of water • .447 psi fsw • .432 psi ffw • Absolute pressure (psia) • Hydrostatic plus Atmospheric

8. Partial Pressure • In a mixture of gasses, the proportion of the total pressure contributed by each gas in the mixture is called the partial pressure • Atmospheric Air: • Approximately 78% nitrogen, 21% oxygen • Component Partial Pressures

9. Pressure in Diving 1 Cu Ft Sea Water = 64 lbs Atmospheric Pressure The Weight of Air Pressure Changes 1 Atm for Each 33 ft in Sea Water (34 ft in Fresh Water). 1 Ft 1 Sq.. In 12 in 12 in 14.7 psi at Sea Level Base Area = 144 Sq. In 64 lbs/144 Sq. In = .445 psi / ft (62.4 lbs/144 Sq. In = .432 psi / ft) Sea Water Pressure Changes .445 psi per ft (Fresh Water Pressure Changes .432 psi per ft) 14.7 psi = 1 Atm

10. The Gas Laws Define Relationship between 3 Factors • Volume • Temperature • Pressure A change in one will result in a measurable change in the others

11. 10 50 10 50 Pressure-Volume Relationship (Boyle’s Law) Volume Pressure High Large Low Small Closed, Flexible Container P1V1 = P2V2

12. Scuba Delivers Air at Ambient Pressure/Density Maintaining Constant Volume Lungs Cannot Expand Therefore, NEVER HOLD YOUR BREATH on Scuba

13. 3000 psi 3150 psi SPG SPG 70 Deg F 100 Deg F Temperature - Pressure - Volume (Charles’ /Gay-Lussac’s) A Direct Temperature-Pressure-Volume Relationship Exists. A Change in Temperature Directly Affects the Volume of a Closed Flexible Container. A Change in Temperature Directly Affects the Pressure Exerted by a Gas in a Closed Rigid Container. The Pressure in a Scuba Tank Will Change by Approx. 5 psi for Every 1 Degree Fahrenheit Change in Temperature.

14. Partial Pressure (Dalton’s Law) Pt = PP1 +PP2 + … Air: 78 % Nitrogen 21 % Oxygen Air = Nitrogen + Oxygen Sea Level - 1 atma 14.7 psia 11.61 psia 3.09 psia 33 fsw 2 atma 29.4 psia 23.52 psia 5.88 psia 66 fsw 3 atma 44.1 psia 35.28 psia 8.82 psia 99 fsw 4 atma 58.8 psia 47.04 psia 11.76 psia 297 fsw 10 amta 147.0 psia 117.60 psia 29.40 psia Note: Pure Oxygen is Toxic at 2 atma (29.4 psia). The Partial Pressure of the Oxygen Component of Air at 297 fsw(10 atma) is 29.40 psia!

15. Solubility (Henry’s Law) Gas Enters a Liquid in Direct Proportion to its Partial Pressure If You Increase the Partial Pressure, the Amount of Dissolved Gas also Increases Reducing Pressure Too Quickly Allows Dissolved Gases to Release Too Quickly and Form Bubbles: The BENDS! DECOMPRESSION SICKNESS (DCS) Prevention: Use the Dive Tables CONSERVATIVELY! DCS Can Occur When Diver Follows Tables

16. Light • Diffusion • Color absorption • Refraction

17. Light Properties Sunlight is Diffused or Absorbed by Particles Suspended in the Water by Light Wavelength According to Depth Surface 10 20 30 40 50 60 70 80 90 100 110 R O Y G B I V Color Loss, Ambient Light

18. Sight Refraction, the Bending of Light Waves, When Changing Transmission Medium, Causes Objects to Appear Closer and Larger Underwater. Actual Size and Location Perceived Size and Location

19. Sound Sound Travels 4X Faster in Water than in Air Time Delay Ears are Calibrated to Air Sound Waves You Can Hear, but Can’t Determine Direction

20. Temperature Relative Body Protection Rqmts 110 90 Lycra 1/8” Wet Suit 70 1/4” Wet Suit Dry Suit 50 30 Heat Loss By Conduction Faster in Water 10 Temp F

21. Heat • Water is 800 times denser than air • Conduction • Convection • Radiation • Thermoclines

22. Physics - Summary Gas Laws Buoyancy Boyle - Volume Use BC/Wt Belt to Regulate Dalton - Partial Pressure Pressure Henry - Solubility One Atm = 14.7 psi Gay-Lussac/Charles - Temp/Pressure/Volume Sound Can’t Determine Direction Temperature Sight Proper Protection Essential Objects Appear Closer/Larger Light Visibility/Colors Decrease w/Depth