The Physics Of Scuba Diving: Swimming With The Fish Essay, Research Paper
The Physics Of Scuba Diving: Swimming with the Fish
Have you ever wondered what it would be like to swim with the fish and
explore the underwater jungle that covers two-thirds of the earth’s surface? I
have always been interested in water activities; swimming, diving and skiing,
and I felt that scuba was for me. My first dive took place while on a family
vacation. I came across a dive shop offering introductory dives, which
immediately caught my interest. After much convincing (my parents), with my
solemn assurance that I would be careful, I was allowed to participate in a dive.
I was ready, or so I thought. The slim basics such as breathing were explained
and I was literally tossed in. Sounds easy enough, right!, well WRONG!!. From
the moment I hit the water, my experience was much less than fun. I quickly
sank to the bottom into a new world, with unfamiliar dangers. I really wasn’t
ready for this experience. I was disorientated, causing me to panic, which
shortened the length of my dive, not to mention my air supply. Let’s just say I
would not do that again.
To start exploring the underwater world, one must first master a few
skills. Certification is the first step of learning to dive. From qualified
professionals one must learn how to use the equipment, safety precautions, and
the best places to dive. This paper is designed to help give a general
understanding of the sport and the importance that physics plays in it. Self-
contained Underwater Breathing Apparatus, or SCUBA for short, is a hell of a lot
of fun. However, there is considerably more to Diving than just putting on a
wetsuit and strapping some compressed air onto ones back. As I quickly learned,
diving safely requires quite a bit more in terms of time, effort, and
preparation. When one goes underwater, a diver is introduced to a new and
unfamiliar world, where many dangers exist, but can be avoided with proper
lessons and understanding. With this knowledge the water is ours to discover.
The Evolution of Scuba Diving
Divers have penetrated the oceans through the centuries for the purpose
of acquiring food, searching for treasure, carrying out military operations,
performing scientific research and exploration, and enjoying the aquatic
environment. Bachrach (1982) identified the following five principal periods in
the history of diving which are currently in use. Free (or breath-hold) diving,
bell diving, surface support or helmet (hard hat) diving, scuba diving, and,
saturation diving or atmospheric diving (Ketels, 4)
The development of self-contained underwater breathing apparatus
provided the free moving diver with a portable air supply which, although finite
in comparison with the unlimited air supply available to the helmet diver,
allowed for mobility. Scuba diving is the most frequently used mode in
recreational diving and, in various forms, is also widely used to perform
underwater work for military, scientific, and commercial purposes.
There were many steps in the development of a successful self-contained
underwater system. In 1808, Freiderich yon Drieberg invented a bellows-in-a-box
device that was worn on the diver’s back and delivered compressed air from the
surface. This device, named Triton, did not actually work but served to suggest
that compressed air could be used in diving, an idea initially conceived of by
Halley in 1716. (Ketels, 9)
In 1865, two French inventors, Rouquayrol and Denayrouse, developed a
suit that they described as “self-contained.” In fact, their suit was not self
contained but consisted of a helmet-using surface-supported system that had an
air reservoir that was carried on the diver’s back and was sufficient to provide
one breathing cycle on demand. The demand valve regulator was used with surface
supply largely because tanks of adequate strength were not yet available to
handle air at high pressure. This system’s demand valve, which was automatically
controlled, represented a major breakthrough because it permitted the diver to
have a breath of air when needed. The Rouquayrol and Denayrouse apparatus was
described with remarkable accuracy in Jules Verne’s classic, Twenty Thousand
Leagues Under The Sea, which was written in 1869, only 4 years after the
inventors had made their device public (Ketels, 10).
Semi-Self-Contained Diving Suit
The demand valve played a critical part in the later development of one
form of scuba apparatus. In the 1920’s, a French naval officer, Captain Yves Le
Prieur, began work on a self-contained air diving apparatus that resulted in
1926 in the award of a patent, shared with his countryman Fernez. This device
was a steel cylinder containing compressed air that was worn on the diver’s back
and had an air hose connected to a mouthpiece. The diver wore a nose clip and
air-tight goggles that undoubtedly were protective and an aid to vision but did
not permit pressure equalization.
The major problem with Le Prieur’s apparatus was the lack of a demand
valve, which necessitated a continuous flow (and thus waste) of gas. In 1943,
almost 20 years after Fernez and Le Prieur patented their apparatus, two other
French inventors, Emile Gagnan and Captain Jacques-Yves Cousteau, demonstrated
their “Aqua Lung.”
This apparatus used a demand intake valve drawing from two or three
cylinders, each containing over 2500 psig. Thus it was that the demand regulator,
invented over 70 years earlier by Rouquayrol and Denayrouse and extensively used
in aviation, came into use in a self-contained breathing apparatus which did not
emit a wasteful flow of air during inhalation (although it continued to lose
exhaled gas into the water). This application made possible the development of
modern open-circuit air scuba gear (Ketels,11).
In 1939, Dr. Christian Lambertsen began the development of a series of
three patented forms of oxygen rebreathing equipment for neutral buoyancy
underwater swimming. This became the first self-contained underwater breathing
apparatus successfully used by a large number of divers. The Lambertsen
Amphibious Respiratory Unit (LARU) formed the basis for the establishment of U.S.
military self-contained diving. This apparatus was designated scuba (for self-
contained underwater breathing apparatus) by its users. Equivalent self-
contained apparatus was used by the military forces of Italy, the United States,
and Great Britain during World War II and continues in active use today. (Ketels,
A major development in regard to mobility in diving occurred in France
during the 1930’s: Commander de Carlieu developed a set of swim fins, the first
to be produced since Borelli designed a pair of claw-like fins in 1680. When
used with Le Prieur’s tanks, goggles, and nose clip, de Carlieu’s fins enabled
divers to move horizontally through the water like true swimmers, instead of
being lowered vertically in a diving bell or in hard-hat gear. The later use of
a single-lens face mask, which allowed better visibility as well as pressure
equalization, also increased the comfort and depth range of diving equipment
Thus the development of scuba added a major working tool to the systems
available to divers. The new mode allowed divers greater freedom of movement
and access to greater depths for extended times and required much less
burdensome support equipment. Scuba also enriched the world of sport diving by
permitting recreational divers to go beyond goggles and breath-hold diving to
more extended dives at greater depths.
The physics of Scuba Diving
Upon entering the underwater world, one notices new and different
sensations as one ventures into a realm where everything looks, sounds and feels
different than it does above the water. These sensations are part of what makes
diving so special.
Understanding why the underwater world is different helps you adapt and
become accustomed to the changes. In the following pages I will attempt to
explain two factors that greatly affect a diver under water: buoyancy and
Have you ever wondered why a large steel ocean liner floats, but a small
steel nail sinks? The answer is surprisingly simple. The steel hull of the ship
is formed in a shape that displaces much water. If the steel used to
manufacture the ocean liner were placed in the sea without being shaped into a
large hull, it would sink like the nail. The ocean liner demonstrates that
whether an object floats depends not only on its weight, but on how much water
it displaces (Ascher, 51).
The principle of buoyancy can be simplified this way: An object placed
in water is buoyed up by the force equal to the weight of the quantity of water
it displaces. The principle of buoyancy is that if an object displaces an
amount of water weighing more than its own weight, it will float. If an object
displaces an amount of water weighing less than its own weight then it will sink.
If an object displaces an amount of water equal to its own weight it will
neither float nor sink, but remain suspended. If an object floats, it is said
to be positively buoyant; if it sinks, it is negatively buoyant; and if it
neither floats nor sinks, it is neutrally buoyant (Kolezer, 16).
It is important for a diver to learn to use these principles of buoyancy
so that the diver can effortlessly maintain his/her position in the water. One
must control buoyancy carefully. When you are at the surface, you will want to
be positively buoyant so that you could conserve energy while resting or
swimming. Under water, you will want to be neutrally buoyant so that you are
weightless and can stay off the bottom and avoid crushing or damaging delicate
corals and other aquatic life. Neutral buoyancy permits a diver to move freely
in all directions (Kolezer, 17).
Buoyancy control is one of the most important skills that a diver could
master, but it is also one of the easiest. A diver, controls his/her buoyancy
using lead weight and a buoyancy control device (BCD). The lead weight, which
is incorporated into a weight system, such as a weight belt is negatively
buoyant. The BCD is a device that can be partially inflated or deflated to
control buoyancy (Kolezer, 19).
Another factor that affects the buoyancy of an object is the density of
water. The denser the water, the greater the buoyancy. Salt water (due to its
dissolved salts) is more dense than fresh water, so you’ll be more buoyant in
salt water than in fresh water – in fact, when floating motionless at the
surface, most divers need to exhale air from their lungs to sink. By exhaling,
the volume of the lungs is decreased, and less water is displaced, resulting in
less buoyancy (Kolezer, 19).
Thus, we can see, that changing the volume of an object changes its
buoyancy. Divers primarily control buoyancy by changing the volume of air in
Body air spaces and water pressure
Although usually not noticeable, air is constantly exerting pressure on
us. An example being as simplified as when walking against a strong wind, what
is actually felt its force pushing against our body. This demonstrates that air
can exert pressure, or weight. One doesn’t usually feel the air’s pressure
because our body is primarily liquid, distributing the pressure equally
throughout our entire body. The few air spaces in our body are- in the ears,
sinuses and lungs- These are filled with air equal in pressure to the external
air. However, when the surrounding air pressure changes, such as when you
change altitude by flying or driving through mountains, some of us can feel the
change as a popping sensation in our ears (Tillman, 40).
Just as air exerts pressure on us at the surface, water exerts pressure
when a person is submerged. Because water is much denser than air, pressure
changes under water occur more rapidly, making one more aware of them.
The weight of the water above a person greatly compounds the amount of
pressure one (ears, lungs, and the air in ones lungs) is under. While it takes
the entire height of the atmosphere to contain a weight of air enough to give 1
atmosphere (1 ATM) of pressure (the pressure one is used to be under as one
walks around daily), it only takes 33 ft. of water to make up an additional ATM
of pressure. Of course, the air is still there too, so at a depth of 33 feet, a
diver is subjected to two Atmospheres of pressure, fully twice what one is
subjected to at the surface! (Resneck, 53)
A diver would have to go really, really deep before being in any danger
of actually being crushed by pressure. It’s what the pressure does to the gases
in your body that can be dangerous. Physics teaches us Boyle’s Law of gases,
which suggests that the volume of a gas is proportional to its pressure. Thus,
when one goes to a depth of, say, 33 feet (1 extra ATM) and fills ones lungs
with a breath of air from a tank and then ascend to the surface without exhaling,
the air in the lungs would expand to twice its volume, causing massive trauma to
the lungs. Other more subtle problems occur with gas under pressure, such as the
accumulation of residual nitrogen in the body’s tissues which can result in
Decompression Sickness (DCS), commonly known as the bends (Tillman, 44).
As with air pressure, one doesn’t feel water pressure on most of ones
body, but we can feel it in our body’s air spaces. When water pressure changes
corresponding with a change in depth, it creates a pressure sensation one can
feel. Through training and experience a diver will learn to avoid the problems
associated with water pressure and the air spaces in our bodies.
As previously mentioned, pressure increases at a rate of one atmosphere
(ATM) for each additional 33 feet of depth underwater. The total pressure is
twice as great at 33 feet than at the surface, three times as great at 66 feet,
and so on. This pressure pushes in on flexible air spaces, compressing them and
reducing their volume. The reduction of the volume of the air spaces is
proportional to the amount of pressure placed upon it.
When the total pressure doubles, the air volume is halved. When the
pressure triples, the volume is reduced to one third, and so on (Tillman, 40).
The density of air in the air spaces is also affected by pressure. As
the volume of the air spaces is reduced due to compression, the density of the
air increases as it is squeezed into a smaller place. No air is lost; it is
simply compressed. Air density is also proportional to pressure, so that when
the total pressure is doubled, the air density is doubled. When the pressure is
tripled the air density triples and so on.
To maintain an air space as its original volume when pressure is
increased, more air must be added to the space. This is the concept of pressure
equalization, and the amount of air that must be added is proportional to the
Air within an airspace expands as pressure is reduced. If no air has
been added to the air space, the air will simply expand to fill the original
volume of the air space upon reaching the surface (Ketels, 76).
If air has been added to an air space to equalize the pressure, this air
will expand as pressure is reduced during ascent. The amount of expansion is
again proportional to the pressure. In an open container, such as the bucket,
the expanding air will simply bubble out of the opening, maintaining it original
volume during ascent. In a closed flexible container, however, the volume will
increase as the pressure is reduced. If the volume exceeds the capacity of the
container, the container may be ruptured by the expanding air (Cramer, 51).
Now let’s take a look at how the relationship between pressure volume
and density affect a diver while diving. Previously it has been mentioned that
air spaces are effected by changes in pressure. The air spaces that a diver is
concerned about are both the natural ones in your body and those artificially
created by wearing diving equipment.
The air spaces within a diver’s body that are most obviously affected by
increasing pressure are found in the ears and sinuses. The artificial air
spaces most affected by increasing pressure is the one created by a divers mask.
During descent, water pressure increases and pushes in your body’s air
spaces, compressing them. If pressure within these air spaces is not kept in
balance with this increasing water pressure, the sensation of pressure builds,
becoming uncomfortable and possibly even painful as the diver continues to
descend. This sensation is the result of a squeeze on the air spaces. A
squeeze is not only a scuba phenomena but may also be experienced in a swimmers
ears when diving to the bottom of a swimming pool. A squeeze, then is a
pressure imbalance resulting in a pain or discomfort in a bodies air space. In
this situation, the imbalance is such that the pressure outside the air space is
greater than the pressure inside (Ketels, 76-77).
Squeezes are possible in several places: ears, sinuses, teeth, lungs and
ones mask. Fortunately, divers can easily avoid all these squeezes.
To avoid discomfort, pressure inside an air space must always equal the
water pressure outside the air spaces. This is accomplished by adding air to
the air spaces during descent, before discomfort occurs. This is called
Compared to the ear and sinus air spaces, the lungs are large and
flexible. As a scuba diver, one automatically equalizes the pressure in the
lungs by continuously breathing from the scuba equipment. When you skin dive,
holding ones breath, the lungs can be compressed with no consequence as long as
they are filled with air when one begins to descent. The lungs will be reduced
in volume during decent and will re-expand during ascent to nearly the original
volume when one reaches the surface (some of the air from the lungs is used to
equalize the other body air spaces) (Ketels, 78).
In a healthy diver, blocking the nose and attempting to gently blow
through it with the mouth closed will direct air into the ear and sinus air
spaces. Swallowing and wiggling the jaw from side to side may be an effective
equalization technique. Some divers even attempt a combination of the previous
As mentioned previously along with squeezes, the lungs experience no
harmful effects from the changes in pressure when holding ones breath while skin
diving. At the start of the skin dive, one takes a breath and descends; the
increasing water pressure compresses the air in the lungs. During ascent, the
air re-expands so that when reaching the surface, the lungs return to their
original volume (Ketels, 78).
When scuba diving, however, the situation is different. Scuba equipment
allows one to breathe under water by automatically delivering the air at a
pressure equal to the surrounding water pressure. This means the lungs will be
at their normal volume while at depth, full of air that will expand on ascent
If a diver breaths normally, keeping the airway to you lungs open, the
expanding air escapes during ascent and your lungs remain at their normal volume.
But, by holding ones breath and then blocking the airway while ascending the
lungs would over expand, much like the sealed bag. Expanding air can cause lung
over-pressurization (lung rupture), the most serious injury that can occur to a
diver. The most important rule in scuba diving is to breath continuously and
never hold your Breath. Lung rupture will occur unless pressure is continuously
equalized by breathing normally at all times (Cramer, 52).
Other physical Phenomena’s
As an air-breathing creature, we have evolved to live on land. Above
the water, we see, hear and move about in a familiar and comfortable manner that
seems normal because we have adapted to an air environment.
Under water, though, one enters a new world, where seeing, hearing,
staying warm and moving are different. This is because water is 800 times more
dense than air, affecting light, sound and heat in ways that we aren’t used to.
Sight seeing is a big part of what diving is all about. One dives for
numerous reasons. A primary purpose is to see new environments, aquatic life
and natural phenomena. Since underwater sight seeing is important, like buying
a new camera, one must learn, how. Therefor when diving, one must know how the
liquid environment affects vision.
To see clearly under water, a mask is needed because the human eye
cannot focus without any air space in front of it. A mask provides the air space.
Without the mask, you can see large objects, but they will be blurred and
indistinct because your eyes cannot bring the rays of light into sharp focus.
Only by wearing a mask can you see sharply (Ascher, 9).
Light travels at a different speed in water than in air. When light
enters the air in your mask from the water, the change in speed causes its angle
of travel to shift slightly. This causes a magnificent effect that makes
objects under water appear 25% larger and closer (Ascher, 52).
Water has other effects on light. As you descend, there is less light.
This is due to several facts: some light reflects off the water’s surface, some
is scattered by particles in the water, and some is absorbed by the water itself.
However, water does not absorb light uniformly.
White light, such as sunlight, is actually composed of various colors
mixed together. The colors are absorbed one by one as depth increases: First
red, followed by orange and yellow. Since each color is part of the total light
entering the water, less light remains as depth increases and each color is
absorbed. For these reason, deeper water is darker and less colorful. To see
true colors, divers sometimes carry underwater lights with them (Resneck, 151).
The underwater world is not a silent world. One can hear many new and
interesting sounds, like snapping shrimp, grunting fish, and boat engines
passing in the distance. Since sound travels farther in water than in air, one
is able to hear things over much longer distances.
Sound also travels about four times faster in water than in air and
because of this, one may have trouble determining the direction a sound is
coming from (Cramer, 95).
Speech is virtually impossible under water because ones vocal cords do
not work in a liquid environment, not to mention the addition of the tube in
ones mouth. Communication by sound is usually limited to attracting the
attention of another diver by rapping on the tank with a solid object, such as a
knife. The diver will hear the rapping, but may not be able to tell where the
sound is coming from.
Heat loss in water.
Diving stops being enjoyable when the diver gets cold. In fact, even a
small loss of body heat has the potential to be a serious health threat. For
these reasons, understanding about heat loss is important.
In air, body heat is lost as it rises from the skin into the air, as it
is carried away by air currents, or as perspiration cools the skin through
evaporation. Water conducts heat away from your body twenty times faster than
air does, meaning that for a given temperature, water has a far greater cooling
effect. Even seemingly warm 86F water can become chilly after a while (Cramer,
The loss of body heat in water can quickly lead to a serious condition
unless you use insulation to reduce the heat loss. Insulation through the use
of exposure suits is recommended for diving in water 75F or colder. Just as one
dresses according to the temperature and conditions to go outdoors, one must
dress appropriately for diving.
Motion in water
One of the best aspects of diving is that it can be so relaxing.
There’s little reason for hurrying. By learning how to move without
breathlessness, cramping or fatigue, you learn to relax during a dive.
Due to the greater density of water, resistance to movement in water is
much greater than in air. If you’ve ever tried to run waist-deep water, you’ve
experienced this. In overcoming this increased resistance while diving, the
best way to conserve energy is to move slowly and steadily. Avoid rapid and
jerky movements that waste energy. Simply take your time. After all this is a
sport to enjoy.
Several months after my vacation, I decided to give scuba diving a
second chance. However, this time I decided to do it right. I signed up to
take a P.A.D.I. certification, which is one of the many internationally
recognized scuba associations. It was here, in a properly structured course,
consisting of both theoretical and practical (in water) sessions where I was
properly re-introduced to the sport.
Since my introductory dive from hell, I have had the chance to become
quite the scuba enthusiast. Partaking in numerous dives not only in warmer
climates (preferably) but in the colder Montreal waters as well, scuba diving
has become part of my lifestyle. I participate in and enjoy every opportunity to
re-visit the underwater world that once scared me away.
In this paper, I included some history of the evolution of the sport in
order to point out that there is more to this particular sport than jumping into
the water. Scuba is a complex sport and can not be enjoyed without some
scientific knowledge. Scuba diving did not simply evolve, but it is the result
of numerous inventions and physical properties. One could only imagine the
difficulty that those historic divers (scientists) had in creating this sport.
My objective in writing this paper was not to deter people away from the
sport, but to stress the importance of the knowledge that is required to
properly and safely partake in it. Like everything else in life, one must work
towards a goal, and this is no different. One will quickly see that the payoff
is far greater than anything else ever experienced. Recreational scuba is meant
to be a very enjoyable and relaxing sport. The scenery is magnificent and the
sensations are truly indescribable.
Today, scuba diving is quickly becoming one of the expanding trades.
Whether for military, research, business, or recreation, hundreds of thousands
of people are heading for the depths, to experience the unknown. My advice for
a new diver is to do it right. Get the proper certification and make each dive
a safe one.
When a diver is fully trained, and in good mental and physical condition,
safe diving can be one of the most enjoyable of experiences. The true beauty of
the underwater world, coupled with the marvelous almost-weightlessness of
floating with neutral buoyancy is an indescribable experience.
Ascher, Scott M. Scuba Handbook for Humans. Iowa : Kendall/Hunt Publishing
Cramer, John L. Ph.D. Skin and Scuba Diving: Scientific Principles and
Techniques. N.Y.: Bergwall Productions, Inc. 1975.
Ketels, Henry & McDowell, Jack. Safe Skin and Scuba Diving, adventure in the
underwater world. Canada : Little, Brown and Company (Canada) Ltd. 1975.
Koelzer, William. Scuba Diving, How to get started. Pennsylvania :Chilton Book
Resneck, John Jr. Scuba, Safe and Simple. New Jersey : Prentice-Hall, Inc. 1975.
Tillman, Albert A. Skin and Scuba Diving. Iowa : Wm. C. Brown Company Publishers.