From Academic Kids
Diving has several meanings:-
- Jumping or falling deliberately, often acrobatically, into water. This, and also completely unequipped swimming underwater, is described on this page. See also Underwater swimming.
- Going underwater with or without breathing apparatus. When done for sport, this is sometimes called subaquatics. See:-
Humans are not the only ones to dive (in sense 1). Some species of amphibious animals such as marine mammals and some seabirds dive to catch their prey underwater. When dealing with equipment such as submarines and underwater remotely operated vehicles, the act of descending into the water is called diving and the command for the descent, especially in battle, is "dive."
Scuba divers sometimes jump into water feet first from some height above the water (e.g. from a large boat or from a pier. Do not jump in head first if you are wearing any sort of scuba equipment or snorkelling equipment. In particular, an open-circuit scuba banging about on the back is big and hard and heavy and during a headfirst dive (in sense 1) may sprain or break the back or neck. Use one hand to hold your mask on.
Sometimes the term jumping is used to disambiguate, e.g. simply for the thrill of entering the water from a high cement tower, we might say that the children jump off the tower, to describe the airborne experience, as well as the impact with the water, but not emphasizing the dive down below the surface of the water, since the intent of jumping off the cement tower is not really to dive down under the water, and in fact the depth of diving into the water is an undesirable effect that can cause barotrauma. Ideally for recreational fun, one would like to jump from a high tower, but not dive too deep after impact.
When people dive in sense 1, they deliberately enter a body of water by jumping in, usually in a posture that minimises drag on entry with arms stretched forwards parallel to straightened legs and torso, typically palms-first, to create a "shadow" for the head.
Competitive swimmers enter the water by diving from a set height above a specially constructed pool. Dives are performed either from springboards, which are long flexible planks that bend as the divers repeatedly jump on the end of the board to gain height and speed before diving; or from rigid platforms of greater height. In elite competition, there are two springboard height competitions, at 1 metre and 3 metres; and a platform competition at 10 metres, but in olympic competition there is only the 3 meter springboard and the 10 meter platform.
Such divers may perform a variety of dives, making somersaults and twists in various orientations and from different starting positions (including platform dives from an initial handstand). Divers are judged on whether they completed all aspects of the dive, the conformance of their body to the requirements of the nominated dive, and the amount of splash created by their entry to the water (less being better). The raw score is then multiplied by a difficulty factor, derived from the number of movements attempted. The diver with the highest total score after a sequence of dives (usually eight in elite competition) is declared the winner.
While not a particularly popular participant sport, diving is one of the more popular Olympic sports with spectators. Successful competitors possess many of the same characteristics as gymnasts, including strength, flexibility, and kinaesthetic judgment.
Synchronized diving was adopted as an Olympic sport in 2004. In this event, two divers form a team and attempt to perform identical dives simultaneously. This is an impressive spectacle, and requires great coordination between the team-mates.
Swimming underwater and diving
The ability to dive and swim underwater can be a useful emergency skill, and is an important part of watersport and navy safety training. More generally, entering water from a height is an enjoyable leisure activity, as is underwater swimming with or without breathing apparatus.
Learning to swim underwater
Assuming that you can swim on the surface, the main obstacle to diving is likely to be the psychological barrier of immersing your head. To overcome this, try hard to keep your eyes open while under the water. Don't be afraid of water getting into your eyes; although chlorinated water can sting, it is not harmful. (Salt water is less irritating.) Your eyes, nose and ears will become accustomed to immersion; plugs and goggles are advisable when there is a risk of infection, for long periods of training, or for competitive swimming.
The crucial step in gaining underwater mobility is adopting a suitable posture. To do this, first try to reach an object on the floor of the pool (or other body of water) that is within your depth. It will be difficult to reach from an upright posture. To get your hands to the object, jump up, bend your body well forward, throw your feet in the air, and try to reach the object, head foremost.
The next exercise might be to swim a few metres towards the object on the surface, and then dive for it. It is difficult at first to get the chest below the surface; but if your legs are thrown well up in the air, their weight will force your body downwards. This is surface diving (also known as a jackknife); some snorkellers and scuba divers call it duck diving.
Swimming underwater should follow quite naturally given some practice. It is largely a matter of maintaining a slightly inverted posture so as to counteract the natural buoyancy of the lungs. Strokes used in surface swimming must be adapted somewhat, and some arm movements (such as the crawl) cannot be used.
Learning to dive into water
Diving in this sense is not as difficult as it looks; again the main barrier is psychological, as diving head-first into the surface seems likely to hurt. To avoid the hurt (and possibly being knocked unconscious) the hands are usually held out (preferably palms-first) to protect the head, since fingertips-first entries often do not cast a large enough "shadow" to protect the head from a high height. Jumping in and landing hands-first tends to avoid water up the nose, but feet first often involves holding the nose. However, if going feet first, the impact often loosens the grip causing water to go up the nose, as well as resulting in one punching one's self in the mouth or otherwise the hands hitting the face on impact in addition to being dislodged from their grip. One problem in learning, is that at first there is impact that causes bruises or pain, but once learning to be streamlined, another problem arises: pain in ears. The ear pain is often absent during initial learning because lack in coordination, etc., causes the body to land in a less streamlined way, so it does not go as deep. Once streamlined, the body goes deep, resulting in immediate and tremendous pain in the ears, from the impact and sudden increase in pressure. Ear plugs seem to mitigate such pain. For safety reasons, diving should always be done into deep water and without goggles, which can damage the eyes by way of sudden increase in pressure. Most eyewear makers, such as Speedo, include instructions that advise against jumping into water with the eyewear on. However, in competitive swimming, the swimmers seem to jump off the starting blocks while wearing eyewear, which seems to run contrary to the advice of the eyewear manufacturers. Competitive swimmers wear specially designed, streamlined racing goggles which are meant to be used while diving. Competitive swimmers usually wear their goggles tighter than recreational swimmers do. This is to keep them from becoming dislodged mid-race. Competitive swimmers use a shallow racing dive which doesn't usually penetrate more than a meter into the water. There is less risk to competitive swimmers of eye injuries for these reasons.
It is best to start by entering some water where the surface is close to or level with the edge. Stoop down until you are nearly double, put your hands together over your head, lean over until they nearly touch the surface, and try to glide, rather than fall, into the water. With practise the height of entry can be increased. Next, you can try taking short run, and leaping head first into the water.
Some pools have increasing heights, 0 m, 1 m, 3 m, 5 m, and 10 m, but others have only limited choices. For example, the Donald Summerville pool in Toronto has only 0 m, 5 m, and 10 m heights available. This means that children learning must move from 0 m to 5 m, which is a large jump in height. At 5 m, adults who are learning often climb back down after seeing the pool from the increased height, since it looks higher from above than down below. Children, however, seem to be less afraid. Children don't seem to need to wear ear plugs, or have as much problems with pain. This may be due to the volume to surface area ratio, e.g. an adult who is twice the height of a child will be eight times as heavy, but present only four times the surface area (volume varies as cube of height; surface area as square of height), resulting in deeper penetration of the water. Perhaps there is also the effect of muscles and bones having a strength that varies as the square of the length, and volume as the cube; this is why ants can fall from great heights with less damage. Therefore, it is much more difficult to learn in adulthood, if one does not learn as a child.
To make a clean entry, you should keep your body, arms, and legs quite stiff, and in a straight line. Tuck your head in so that your hands break the surface in front of it.
Feet first or hands first
Hands first results in more streamlined entry, and less pain, if things work out correctly, but since the body needs to change orientation 180 degrees, things can go wrong, such as having legs bent, resulting in bruised thighs. The bruises that swell up usually go away after about 14 days or so. Once getting streamlined, then ears will hurt. Feet first is less streamlined, and also the nose is facing the "wrong" way, and water is blasted up the nose. To avoid this "nose enema", one hand may be used to hold the nose. Usually the hand will be pulled off, unless it is tucked in tight. Using the other arm to hold the first arm in tight helps in this regard, since the outer arm gets yanked away at time of impact, but the inner arm sometimes remains holding the nose. Crossing the legs when going feet first tends to reduce the effective impact on the genitalia, which might otherwise be felt as "referred pain" in the abdomen. When going feet first there is a choice in pointing the toes, more or less. More pointed (streamlined) impacts further up (genitalia, nose, etc.), and not pointed helps to bear the brunt of the water on the feet, which are often hard and calloused from walking barefoot on gravel roads (sometimes people wear shoes if doing feet-first entries from large heights).
If going hands first, it is important to keep arms out to protect the head. Looking down at the water will likely result in a badly bruised face, but some people take that risk and quickly pull the head in just before impact. When doing so, a common mistake is to overshoot, and to pull the head in too far, bruising the top of the head. Thus it seems easiest to keep the head steady, and also this allows the shoulders to be brought in to help protect the ears when the arms are extended. Fingers should not be interlocked, or they may be broken or damaged. The most recommended way is to, with hands together, facing open palms towards the water to bear the brunt of the impact. There are several benefits to this method, such a reduction of impact speed felt by the rest of the body (less injuries), dispersion of local surface tension (less injuries, pain, splash), and most importantly protection for the head. If done properly, it's surprisingly streamlined, because the flat palms generate sizable air bubbles that encase most of the body so that the body is gliding through air immediately after impact. The air bubbles later dissipate by slowly bubbling to the surface, instead of having one big splash. A good streamlined entry results in less sudden energy transfer/dissipation, and therefore less pain and bruising, except on the palms which are usually tough enough to withstand the approximately 300 pounds or so of impact force from a height of 10meters (approximately 14 pounds per square inch of water column).
One non-standard diving (class 1) method sometimes seen is entering the water in the fetal position bottom first, making a big splash. This is sometimes called bombing. If done from excessive height, there is a risk of the impact pressure pumping water into the anus. It also may wet people standing beside the pool. Blunt entries of this sort will also result in bruising, if done from any but the lowest towers.
Another undesired entry attitude is the bellyflop. In it, the body enters the water horizontally or nearly so, belly down.
The effect of height on the dive
The following table summarizes velocity of impact, and time-in-the-air, from the various standard heights of 1 m, 3 m, 5 m, and 10 m, that are found in municipal swimming baths, as well as from greater heights. The impact velocity and time of impact vary as the square root of the height. Heights beyond 10 m are not commonly found at municipal swimming baths, but exist at "use at your own risk" places such as bridges and cliffs. Cliff jumping, a common pastime for daredevil children, often takes place at heights of 20 m to 30 m. There is a limit to how high one can jump from and survive, regardless of water depth. For example, the Golden Gate Bridge is 220 feet (66 m) high and overlooks water deep enough to not hit the bottom, but the result is certain death. Thus the 66 m jump listed below is only used for suicide, but the other heights are typical of recreational bathing. Although 66 m is a "lethal dose", children often jump from 30 m (approximately 50% lethal dose) for recreation. This can be quite dangerous (e.g. if landing badly, or hitting a branch or dead fish or other object floating on the surface). The impact can also knock him unconscious, and, in absence of lifeguards (i.e. bridge jumping or cliff jumping), can cause drowning, even if from less than the lethal height.
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