Diving Physics

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# Diving Physics - PowerPoint PPT Presentation

Diving Physics. We will cover. Pressure Behaviour of Gases Vision Sound Buoyancy. 1 Bar. Atmospheric Pressure Results from the weight of this air. Normal Atmospheric Pressure = 1 Bar = 1 AT = 1 Kg/cm 2. Pressure. A column of air rising above one sq. cm. of the

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## Diving Physics

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Presentation Transcript

### Diving Physics

We will cover
• Pressure
• Behaviour of Gases
• Vision
• Sound
• Buoyancy

1 Bar

Atmospheric Pressure Results from the weight of this air

Normal Atmospheric Pressure

= 1 Bar = 1 AT = 1 Kg/cm2

Pressure

A column of air rising above one

sq. cm. of the

Earth’s surface

Atmospheric

and

Water Pressure

Absolute Pressure

is the sum of

1 Bar

2 Bar

10 Metres

1 Bar

Pressure
Pressure

0 Metres

1 Bar

10 Metres

2 Bar

20 Metres

3 Bar

30 Metres

4 Bar

40 Metres

5 Bar

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

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.

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

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

Boyle’s Law

“At constant temperature, the volume of a given mass of gas varies inversely with the ABSOLUTE pressure”

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
Dalton’s Law

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

Dalton’s Law(Example)
• Pure air at 1 Bar pressure
• Air consists 79% nitrogen and 21% oxygen
• Partial pressure of nitrogen =.79 Bar P.P.
• Partial pressure of oxygen =.21 Bar P.P.
Dalton’s Law of Partial Pressure

0 1.0 .21 .79

10 2.0 .42 1.58

20 3.0 .63 2.37

30 4.0 .84 3.16

40 5.0 1.05 3.95

50 6.0 1.26 4.74

Depth Absolute

Metres Pressure ppO2 ppN2

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)

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”

P

V

P

V

1

1

2

2

=

200

12

P

12

T

T

x

x

=

2

1

2

283

313

313

x

200

x

12

P

=

2

283

x

12

Universal Gas Law Examples

= 221 Bar

Universal Gas Law Examples

Total contents in litres of cylinder:200(P1) x 0.4(V1) = 80 litres

At 30 metres the effective contents will be:80/4 = 20 litres

Giving 11/4 fills at this depth

Universal Gas Law Examples

A diver breathes at a rate of 28L/min. How long will a 10L/232 Bar cylinder last at 20M ?

What is the volume of air available at 20M ?

P

x

V

232

x

10

=

=

1

1

V

2

P

3

2

Universal Gas Law Examples

P1 = 232 Bar V1 = 10L P2 = 3 Bar V2 = ?

= 773.3L available at 20M

773

.

3

Time

=

28

Universal Gas Law Examples

Breathing at 28L/min. How long will 773.3L last

= 27.6 minutes

Vision Underwater

Light

Light

Air

Air

Water

Water

Vision Underwater

Fish appears

Larger and Closer

RED

ORANGE

YELLOW

GREEN

BLUE

VIOLET

GREY

5

8

11

19

23

28

31

Colour Absorption

DEPTH (metres)

Sound

4 times faster

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”

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

Buoyancy - Archimedes Principle

Wood

Steel

WOODSTEEL

Volume occupied by block 1000 cm3 1000 cm3

Weight of displaced water 1.0 kg 1.0 kg

Weight of object 0.7 kg 5.0 kg

Weight of object in water -0.3 kg +4.0 kg

Summary
• Pressure
• Behaviour of Gases
• Vision
• Sound
• Buoyancy