Diving Physics

Front 1

Why do colors appear different under water?

Back 1

Colors are different because some of them are absorbed by water very differently than by air.

Front 2

Is water a better conductor of heat than air?

Back 2

Yes. We lose heat much more quickly in cold water. Water is also more denser than air.

Front 3

How much more approximately does water weigh than air, at sea level?

Back 3

Water weighs about 800 times more than air. As you dive, you are quickly subjected to very substantial pressure. The gasses inside the human body, are much more subject to change.

Front 4

What is buoyancy?

Back 4

It is the tendency or capacity to stay afloat in a determined liquid.

Front 5

Who was Archimedes?

Back 5

He was a Greek scientist who lived more than 2,000 years ago.

Front 6

What did Archimedes find regarding buoyancy?

Back 6

He observed that an object that is partly or fully immersed in water is pushed upwards by a force that is equal to the weight of the fluid that is displaced.

Front 7

What is "neutral buoyancy"?

Back 7

It means that the divers body and whatever gear is worn or carried is as exactly as dense as the water. Interpreted into Archimedes findings, you just float in place and neither rise nor sink. Explained another way, if the sum total of your body is less dense than the surrounding water you are positively buoyant and you rise. if the diver and his gear is denser, than he is negatively buoyant, and he sinks.

Front 8

What are the three major ways to control buoyancy?

Back 8

1. Adding weights. The usually amount to about 10% of the body weight.
2. Buoyancy compensator(BC) or referred to as a Buoyancy control device, (BCD).
3. Lung buoyancy. Most are positively buoyant in water with their lungs fully aerated, but negatively when the air is released from the lungs.

Front 9

Where does the BC get its air from?`

Back 9

It gets its air from the scuba tank and is employed to adjust buoyancy at various depths. It is considered a safety device.

Front 10

What other factors determine "buoyancy"?

Back 10

1. The size and weight of the diver.
2. The type of diving suit.
3. The weight belt
4. Design and weight of the scuba unit
5. The air in the BC.
6. The air in the lungs.
7. The remaining air in the tank.
The stuff the diver carries with himself.
8. Whether one is diving in salt or fresh water.

Front 11

Saltwater contains dissolved minerals, but mostly salt. True/False

Back 11

True. There is about 30-35 pounds of salt in 1,000 pounds of water. Seawater is denser, and promotes a much more positive buoyancy.

Front 12

gasses are of very low density compared to water. True/False

Back 12

True.Water does not compress at all. gas compresses quite easily.
What we call air, is actually a number of gases.

Front 13

What is the most important and significant of gases?

Back 13

Oxygen. Its chemical symbol is "O" and its atomic number is 8. It is the 2nd most common element on earth and roughly makes up about 21% of the air we breathe. Too much can be poisonous.

Front 14

For diving purposes, what is the second most significant gas?

Back 14

Nitrogen(N). Its atomic number is 7. It is the largest component of our air, which is app. 78%.
Above water, whatever N is breathed in is usually exhaled. Some N gets absorbed by our bodies and just remains there.

Front 15

What is contained in the 1% of air that remains?

Back 15

A variety of elements such as Argon, Neon, Helium, methane, Krypton, Hydrogen, Carbon Dioxide and others.With the exception of CO2, the other gases have really no significance.

Front 16

Is there a problem with N for Divers?

Back 16

Absolutely. When you dive, the increased pressures of the water compresses N and more of it will dissolve into your body. There are N saturation points under water.

Front 17

What do saturation points depend on?

Back 17

They depend on the depth, the type of body tissue involved, and how long a diver is exposed to the increased pressure.

Front 18

The deeper you dive, the more N your body absorbs. True/false. In fact, the deeper you go, the larger the difference between the N already absorbed in your body and what it can now hold, which means more N gets absorbed at an even faster rate.

Back 18

True. In fact, the deeper you go, the larger the difference between the N already absorbed in your body and what it can now hold, which means more N gets absorbed at an even faster rate.

Front 19

At depths of app. 100ft or so, N can result in N narcosis. True/False

Back 19

True Absorbing the N as one descends is not as preoccupying as releasing the N as one ascends.

Front 20

What happens when a diver ascends?

Back 20

As pressure diminishes, N starts dissolving out of tissues. This is referred to as "off gassing".This results in the formation of tiny N bubbles that then get carried out to the lungs and breathed out.

Front 21

What is the concern if there is too much N?

Back 21

If there is too much N, and it is released too quickly, small bubbles will combine to form bigger bubbles, and these can do damage to the organism. Joint pain, breathing difficulty and if severe enough, death. (Decompression sickness) (Bends) (Caisson's)

Front 22

Is there a way to know how much N is absorbed?

Back 22

Yes. There are Dive Tables that calculate how much N is absorbed and can be safely released

Front 23

Each individual diver is different and will absorb and release N in a different manner. True/False

Back 23

True. different body tissues have different absorption/diffusion ratios.

Front 24

Give an example of tissue that are slow to absorb and release N?

Back 24

Cartilage and bone.
Lung tissue is very fast.
Body fat has a much greater affinity for N absorption, and can impact decompression significantly.

Front 25

What does Boyle's law say?

Back 25

It says that as gas pressure increases, gas volume decreases.

Front 26

What is Charles' law?

Back 26

It says that with constant pressure, gas volume increases and decreases with its temperature.

Front 27

What is dalton's law?

Back 27

In a mix of gases, the total gas pressure is equal to the sum of their individual pressures.

Front 28

What is Henry's law?

Back 28

That the amount of gas that will dissolve in a liquid is a function of its partial pressure and how easily the liquid absorbs gas.

Front 29

What is meant by one atmosphere?

Back 29

It is the air pressure at sea level.It also translates into 14.7 pounds/sq. in. or 14.7psi.

Front 30

What happens at a depth of 33 feet of water regarding pressure?

Back 30

The pressure doubles. This means that gas down there is compressed to half its volume. This means that every regular breath of air actually takes in twice as many air molecules as on the surface. As a result, air in the tank will last only half as long.

Front 31

What happens for each additional 33 feet of depth?

Back 31

The pressure increases by another atmosphere.

Front 32

What is the total pressure at 33 feet and at 66 feet respectively?

Back 32

At 33 feet the total pressure is 2 atmospheres, and 3 atmosphere at 66 ft.

Front 33

What is the pressure in atmospheres at 100 feet?

Back 33

It is 4 atmospheres. The air in the tank will last only a quarter of the time it would relative to the surface.

Front 34

Imagine taking a breath of air at a depth of 33 feet, then holding your breath and ascending to the surface. What can happen?

Back 34

The air will expand to twice its size, which can lead to abnormal presence of air around the lungs.

Front 35

As a result of too much air around the lungs, pneumothorax can result. True/false

Back 35

True.This can result in lung collapse.
It can also cause the formation of an arterial air embolism.
Mediastinal emphysema is when air is trapped in the center of the chest.
If air bubbles find their way under the skin, this can result in subcutaneous emphysema.

Front 36

When scuba diving, one should never hold ones breath. True/ False.

Back 36

True, and True again.

Front 37

Can one say that Charles law describes why a scuba cylinder being filled with air gets quite hot?

Back 37

Yes. But, once it cools down, the pressure inside the tank is now lower. gas pressure gets lower, when the gas gets cooler.

Front 38

Relating to Dalton's law,if a bad compressor pumps some CO into the tank, at the surface that would not do much damage. But what is the consequence at depth?

Back 38

The CO inhaled could be deadly. While the percentage of CO stays the same, at say, 100 ft, one would still breath in 4 times as many CO molecules, more than enough to do damage. Even O2, can become toxic at such depths.

Front 39

Because of tissue variation regarding gas absorption and release, and that people differ in size and shape, it can be very difficult to predict to accurately predict ingassing and the much more dangerous outgassing into and out of tissue. True/False

Back 39

True. Dive tables and computers have data that show safe rates of descent.

Front 40

Regarding Nitrogen, if you start out at sea level and then drive up a mountain to dive in a mountain lake, which is app. 6000 ft in elevation, howdoes that affect the N levels in your body?

Back 40

You will start out having residual N in your body. Your first dive should be treated as a repetitive dive, unless you wait long enough for your body to first tatoally adjust to the new altitude.

Front 41

When using a PADI system, one should assume that each 1,000 feet of additional elevation is equivalent to 2 pressure groups. One should always round up. True/False

Back 41

True.

Front 42

Does one see different underwater?

Back 42

Yes. The diving mask, with its flat glass lens, bends light so that objects underwater are magnified by about 1/3rd. Inexperienced divers tend to underestimate the distance of close objects, and overestimate the distance to objects farther away.

Front 43

Are colors different underwater as well?

Back 43

Yes.Colors are different wavelengths reflected by an object. Underwater waves ravel differently, and some wavelengths are filtered out by water sooner than others.

Front 44

Which energy wavea are absorbed first?

Back 44

Lower energy wavea are absorbed first, so red disappears first, then orange, then yellow. Green stays longer, and blue the longest, which is why things look bluer the deeper you go.

Front 45

What happens in murky water?

Back 45

There is less light penetration and things tend to look greenish yellow.

Front 46

How far down can colors be observed?

Back 46

Even in clear conditions colors can only be seen down to a depth of just over 100ft. Below this, objects look black to gray.

Front 47

Does the water surface have an effect on light. Absolutely.

Back 47

The water surface is reflective and can act like a mirror. At noon, with the sun being right overhead, almost all of the suns light enters the water. Early or late in the day, when the suns rays hit the water at different angles, almost all light is reflected away, and doesn't make it into the water. It can get dark sooner than one thinks.

Front 48

Sound travels much faster in water, than in air. True/False

Back 48

True. It travels about 4 times as fast. Sound also travels farther in the water. This is why the military is concerned with silent submarines.

Front 49

Can sound be affected by other variables in the water?

Back 49

Yes. It can be affected by water pressure, temperature and salinity.

Front 50

Water is a much better conductor of heat than air is. True/False

Back 50

True. When diving, the water that comes into contact with your body warms up, expands, and quickly carries the heat away from you. One feels cold quickly.
Water remove heat from the body 25=30 times faster than air.

Front 51

Can breathing be a factor regarding heat loss?

Back 51

Yes.Breathing accounts for about a quarter of our body's heat loss in the form of exhaled warm air. the deeper we dive, the denser the air we inhale.

Front 52

What happens at a depth of 33 ft regarding inhalation and heat loss?

Back 52

At 33 ft the air we breathe in and exhale is already twice as dense as on the surface, which means that the heat loss from exhaling is as well, twice as large.