Diving
Diving is moving under water. Scuba divers use breathing devices, while freediving happens without them.Breathing apparatus includes most commonly a cylinder filled with compressed air which is supplied to the diver through a regulator. The air is exhaled into the water through the regulator (bubble cloud). Another possible breathing apparatus is so called closed-circuit apparatus which allows recycling of exhaled gases. The system removes the carbon dioxide and releases the oxygen for re-use. The closed circle apparatus enables longer diving, but is much more complex and require more precise maintenance and special training. There is also surface-supplied diving equipment, used especially by professional divers.
If the diver rises too fast from deep water, there is a risk that gases, nitrogen in particular, are decomposed in blood into separate gas bubbles which can block blood flow when the pressure is decreasing too fast. This condition is called divers' disease or decompression sickness. It is very rare among recreational divers.
Freediving
While freediving has been a professional activity especially for pearl and sponge divers, nowadays it is becoming a popular sport. It is possible to get divers' disease even when freediving if you dive aggressively enough. Even though there is not much nitrogen in lungs, the pressure makes it dissolve in blood to some degree. At great depths, nitrogen has time to accumulate in blood so that there is a possibility of divers' disease. You should never dive alone because of the drowning risk.Freediving has a number of different types of dive that are recognized competitively. e.g. dynamic apnea, constant weight, and static apnea. In addition, there are many types of vertical diving done with equipment, all of them not being competitive.
Equipment
Scuba diving use compressed gas cylinders that supplies air to diver with the help of pressure regulator.Divers use almost always so-called basic equipment, including diving masks, snorkels and fins. In addition to this basic equipment and a diving suit, scuba diving equipment also includes a knife, different kinds of lamps, orientation equipment, depth indicators, and dive computers.
To control buoyancy, divers use buoyancy control devices, BCD, that are filled or emptied with gas. Divers attempt to have as neutral lift as possible so that they don't float or sink. In this way, moving under water is effortless and pleasant, and economic considering gas consumption. Usually divers need to compensate the positive lift with lead weights attached to a weight belt or BCD. Divers wearing dry suits control the buoyancy also with their suits.
Suits
Divers use wetsuits or dry suits of different thicknesses depending on water temperature. The difference between wetsuit and drysuit is that while water gets through wetsuit, drysuit is waterproof and stays completely dry.Insulating feature of wetsuit is based on a thin, almost stable layer of water between the suit and the skin, the layer that gets warm thanks to diver's own body temperature, and on the insulating neoprene surface of the wetsuit.
Dry suits get their insulation from thermal undersuits and from the air inside them. In extreme conditions, you can fill the drysuit with argon that has lower thermal conductivity than air, keeping your body warm longer.
In addition, there are drysuits made of neoprene. The advantage of these suits is their insulating surface layers. You need less clothes under them than you need under traditional rubber and nylon suits, and they are more form-fitting and streamlined. The disadvantage is the fact that neoprene is compressed by increasing water pressure, which lowers insulation capability in depths. Neopren suits are also heavier than traditional drysuits, although it doesn't matter in water.