Question: How are Free-diving and Scuba diving different?
About the article "Snorkeling", section "Variants and related activities".

Candidate passages:
Underwater diving is the practice of going underwater, either with breathing apparatus (scuba diving and surface supplied diving) or by breath-holding (freediving).
Atmospheric diving suits or the saturation diving technique can be used to combat decompression sickness.
Diving activities are restricted to relatively shallow depths, as even armored atmospheric diving suits are unable to withstand the pressures of most of the deeper waters of the world.
Diving is also restricted to conditions which are not excessively hazardous, though the level of hazard acceptable to the diver can vary considerably.
Occasionally divers may dive in liquids other than water.
The term deep sea diving refers to underwater diving, usually with surface supplied equipment, and often refers specifically to the use of standard diving dress with the traditional copper helmet.
Hard hat diving is any form of diving with a helmet, including the standard copper helmet, other forms of free-flow helmet and lightweight demand helmets.
Recreational diving is a popular activity (also called sports diving or subaquatics).
Technical diving is a branch of recreational diving.
Professional diving (commercial diving, diving for scientific research purposes or diving for financial gain) takes a range of diving activities to the underwater work site.
Public safety diving is the underwater work done by law enforcement, fire rescue, and search & rescue/recovery dive teams, and may be done by professionals or volunteers.
Military diving includes combat diving, clearance diving and ship's husbandry diving.
Underwater sports is a group of competitive sports using either free-diving, snorkelling or scuba technique, or a combination of these techniques.
Training, types of equipment used and breathing gases used depend on the type of diving. 
  Surface supplied diving - mostly used in professional diving.
This category includes: * Surface oriented surface supplied diving (Bounce diving), where the diver starts and finished the dive at normal atmospheric pressure.
* Saturation diving, where the diver remains under pressure in an underwater habitat or saturation spread between underwater excursions.
* Standard diving dress - mostly used in professional diving.
Mainly of historical interest now.
* Airline or Hookah diving.
* "Compressor diving" - a rudimentary form of surface supplied diving used in the Philippines by artisanal fishermen.
* Recreational forms like snuba.
Scuba diving - The use of self-contained underwater breathing apparatus.
This category includes: * Open-circuit scuba consisting of diving cylinder(s) and diving regulator(s) * Rebreather, closed-circuit or semi-closed-circuit scuba  Free diving or breathhold diving, where the diver completes the dive on a single breath of air taken at the surface before the dive.
* Snorkel allows breathing at the surface with the face submerged, and is used as an adjunct to free diving and scuba.
Atmospheric diving suits and other submersibles which isolate the diver from the ambient environment.
These are not considered here.
Liquid breathing systems are extremely rare and at an early experimental stage.
It is hoped that some day practical systems allow very deep diving.
This is not considered here.  
 Try Scuba Diving  
The river is a popular scuba diving location and the valley is used for bungee jumping.
The diving conditions are usually best from late spring to early autumn. 
  Scuba, which is commonly used in recreational diving, is the main alternative to surface supplied diving equipment.
Scuba is available in open circuit and rebreather configurations.
Atmospheric diving suits such as the JIM suit and the Newtsuit isolate the occupant from the ambient pressure, but are bulky and extremely expensive.
Manned and unmanned submersibles (ROVs and AUVs) have their applications, but lack the dexterity of a diver at present (2011).
Free diving, or breathhold diving, is extremely limited in duration and relatively high risk.