question: Why does 72 degree water feel so much colder than 72 degree air?
comment: Water has a much higher thermal conductivity than air, meaning it will transfer heat (or cold) through it faster, ultimately removing energy from your skin faster.
passages: BULLET::::- Thermal conductivity of water is higher than that of air. As water conducts heat 20 times more than air, divers in cold water must insulate their bodies with diving suits to avoid hypothermia. Gases used in diving have very different thermal conductivity; trimix conducts heat more than air and argon conducts less heat than air hence the reason many trimix divers inflate their drysuits with argon.
   Section::::Calibration.:Equivalent temperature.
   Heat transfers very well into water, and body heat is therefore lost extremely quickly in water compared to air, even in merely 'cool' swimming waters around 70F (~20C). A water temperature of can lead to death in as little as one hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes. This is because cold water can have other lethal effects on the body, so hypothermia is not usually a reason for drowning or the clinical cause of death for those who drown in cold water.
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  "Q" = the dry heat loss, or power, recorded by the manikinbr
  
  "t" = the skin temperature of the manikinbr 
  
  "t" = the equivalent temperature of the room (the calibration temperature)
  
  This factor may then be used to calculate equivalent temperature during further experiments in which radiant temperature and air velocity are not controlled using the equation:br
  
  Section::::Setup.
   BULLET::::- In lakes exposed to geothermal activity, the temperature of the deeper water may be warmer than the surface water. This will usually lead to convection currents.
  
  BULLET::::- Water at near-freezing temperatures is less dense than slightly warmer water - maximum density of water is at about 4°C - so when near freezing, water may be slightly warmer at depth than at the surface.
   BULLET::::- In the US and Canada, the R-value that describes the performance of thermal insulation is typically quoted in ft⋅°F⋅hr/Btu. For one square foot of the insulation, one BTU per hour of heat flows across the insulator for each degree of temperature difference across it.
  
  BULLET::::- 1 "therm" is defined in the United States and European Union as 100,000 Btu—but the U.S. uses the Btu while the EU uses the Btu. The therm is used in natural gas pricing in the United Kingdom.
   BULLET::::- "U" – specific internal energy in kilojoules per kilogram
  
  BULLET::::- "S" – specific entropy in kilojoules per kilogram-kelvin
  
  BULLET::::- "c" – specific heat capacity at constant pressure in kilojoules per kilogram-kelvin
  
  BULLET::::- "γ" – Thermal expansion coefficient as 10 per kelvin
  
  BULLET::::- "λ" – Heat conductivity in milliwatts per meter-kelvin
  
  BULLET::::- "η" – Viscosity in micropascal-seconds (1 cP = 1000 µPa·s)
  
  BULLET::::- "σ" – surface tension in millinewtons per meter (equivalent to dyn/cm)
  
  Section::::Additional data translated from German "Wasser (Stoffdaten)" page.:Physical and thermodynamic tables.:Standard conditions.
   Most performance and flight planning graphs and tables use either degrees Celsius or Fahrenheit or both. The Kelvin scale, however, is used for Mach number calculations. For example, the speed of sound in dry air is 
  
  where:
  
  Section::::Aviation usage.:Sources.
   BULLET::::1. within the peak of the blackbody radiation expected from the Earth, and
  
  BULLET::::2. able to transmit adequately well through the atmosphere
   Section::::Influencing factors.:Relative humidity.:Interplay of temperature and humidity.
  
  Various types of apparent temperature have been developed to combine air temperature and air humidity. 
  
  For higher temperatures, there are quantitative scales, such as the heat index.
  
  For lower temperatures, a related interplay was identified only qualitatively:
  
  High humidity and low temperatures cause the air to feel chilly.
  
  Cold air with high relative humidity "feels" colder than dry air of the same temperature because high humidity in cold weather increases the conduction of heat from the body.
   Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or written as a degree. The kelvin is the primary unit of temperature measurement in the physical sciences, but is often used in conjunction with the degree Celsius, which has the same magnitude. 
  
  Section::::History.
   Thermal comfort as a "condition of mind" is "defined" in psychological terms. Among the factors that affect the condition of mind (in the laboratory) are a sense of control over the temperature, knowledge of the temperature and the appearance of the (test) environment. A thermal test chamber that appeared residential "felt" warmer than one which looked like the inside of a refrigerator.
  
  Section::::Models.:Adaptive comfort model.:Physiological Adaptation.
   Section::::See also.
  
  BULLET::::- Atmospheric temperature
  
  BULLET::::- Body temperature (thermoregulation)
  
  BULLET::::- Color temperature
  
  BULLET::::- Dry-bulb temperature
  
  BULLET::::- Heat conduction
  
  BULLET::::- Heat convection
  
  BULLET::::- Instrumental temperature record
  
  BULLET::::- ISO 1
  
  BULLET::::- ITS-90
  
  BULLET::::- Laser Schlieren Deflectometry
  
  BULLET::::- List of cities by temperature
  
  BULLET::::- Maxwell's demon
  
  BULLET::::- Orders of magnitude (temperature)
  
  BULLET::::- Outside air temperature
  
  BULLET::::- Planck temperature
  
  BULLET::::- Rankine scale
  
  BULLET::::- Relativistic heat conduction
  
  BULLET::::- Satellite temperature measurements
  
  BULLET::::- Scale of temperature
  
  BULLET::::- Sea surface temperature
  
  BULLET::::- Stagnation temperature
  
  BULLET::::- Thermal radiation
  
  BULLET::::- Thermoception
  
  BULLET::::- Thermodynamic (absolute) temperature
  
  BULLET::::- Thermography
  
  BULLET::::- Thermometer
  
  BULLET::::- Virtual temperature
  
  BULLET::::- Wet-bulb globe temperature
  
  BULLET::::- Wet-bulb temperature
   The thermal conductivities of common substances span at least four orders of magnitude. Gases generally have low thermal conductivity, and pure metals have high thermal conductivity. For example, under standard conditions the thermal conductivity of copper is over times that of air.
  
  Of all materials, allotropes of carbon, such as graphite and diamond, are usually credited with having the highest thermal conductivities at room temperature. The thermal conductivity of natural diamond at room temperature is several times higher than that of a highly conductive metal such as copper (although the precise value varies depending on the diamond type).
   BULLET::::- "U" is the rate of heat transfer across the building envelope per degree temperature difference between outdoor and indoor temperature and per unit floor area, given in W/°C/m (Btu/s/°F/ft). This heat transfer can vary due to variations of fresh air ventilation rate but is largely considered constant to a first order approximation.
   BULLET::::- Thermoclines, or sudden changes in temperature. Where the air temperature is higher than the water temperature, shallow water may be warmed by the air and the sunlight but deeper water remains cold resulting in a lowering of temperature as the diver descends. This temperature change may be concentrated over a small vertical interval, when it is called a thermocline.
  
  BULLET::::- Where cold, fresh water enters a warmer sea the fresh water may float over the denser saline water, so the temperature rises as the diver descends.
   There are a variety of techniques for measuring this parameter that can potentially yield different results because different things are actually being measured. Away from the immediate sea surface, general temperature measurements are accompanied by a reference to the specific depth of measurement. This is because of significant differences encountered between measurements made at different depths, especially during the daytime when low wind speed and high sunshine conditions may lead to the formation of a warm layer at the ocean's surface and strong vertical temperature gradients (a diurnal thermocline). Sea surface temperature measurements are confined to the top portion of the ocean, known as the near-surface layer.
   Surface temperature
  
  Surface temperature is the temperature at or near a surface. 
  
  Specifically, it may refer to:
  
  BULLET::::- Surface air temperature, the temperature of the air near the surface of the earth
  
  BULLET::::- Sea surface temperature, the temperature of water close to the ocean's surface
  
  BULLET::::- Surface temperature of a star, often the effective temperature
  
  Section::::See also.
  
  BULLET::::- Instrumental temperature record, the historical record of in situ measurements of surface air and sea temperatures
  
  BULLET::::- Pyrometer, a device that remotely determines the temperature of a surface
  
  BULLET::::- Infrared thermometer, a type of pyrometer
   BULLET::::- Saturation (genetic), the observed number of mutations relative to the maximum amount possible
  
  BULLET::::- Ocean saturation, more than 2.3 billion years ago: see "Great Oxygenation Event"
  
  Section::::Physics.
  
  BULLET::::- Colorfulness § Saturation, see also: "Saturation intent", a rendering intent in color management
  
  BULLET::::- Thermodynamic state at lower temperature bound of superheated steam
  
  BULLET::::- Saturation (magnetic), the state when a magnetic material is fully magnetized
  
  BULLET::::- Saturated fluid or saturated vapor, contains as much thermal energy as it can without boiling or condensing
   Apparent temperature
  
  Apparent temperature is the temperature equivalent perceived by humans, caused by the combined effects of air temperature, relative humidity and wind speed. The measure is most commonly applied to the perceived outdoor temperature. However it also applies to indoor temperatures, especially saunas and when houses and workplaces are not sufficiently heated or cooled.
  
  BULLET::::- The heat index and humidex measure the effect of humidity on the perception of temperatures above . In humid conditions, the air feels much hotter because less perspiration evaporates from the skin.
   Common scales of temperature measured in degrees:
  
  BULLET::::- Celsius (°C)
  
  BULLET::::- Kelvin (K)
  
  BULLET::::- Fahrenheit (°F)
  
  BULLET::::- Rankine (°R or °Ra), which uses the Fahrenheit scale, adjusted so that 0 degrees Rankine is equal to absolute zero.
  
  Other scales of temperature:
  
  BULLET::::- Delisle (°De)
  
  BULLET::::- Newton (°N)
  
  BULLET::::- Réaumur (°R)
  
  BULLET::::- Rømer (°Rø)
  
  BULLET::::- Wedgwood (°W)
  
  Section::::Kelvin.
  
   (Measurement of temperature) 
   Water conducts heat around 25 times more efficiently than air. Hypothermia, a potentially fatal condition, occurs when the human body's core temperature falls below 35 °C. Insulating the body's warmth from water is the main purpose of diving suits and exposure suits when used in water temperatures below 25 °C.
  
  Section::::Physical characteristics.:Acoustic properties.
   The density of most liquids is nearly constant (isopycnic), so it can be stated that their densities vary only weakly with pressure and temperature. Water, which varies only a few percent with temperature and salinity, may be approximated as barotropic. In general, air is not barotropic, as it is a function of temperature and pressure; but, under certain circumstances, the barotropic assumption can be useful. 
   Section::::Minimum detectable temperature difference.
  
  Minimum detectable temperature difference (MDTD), also called minimum detectable temperature (MDT), is not the same phenomenon as MRTD and is only subtly different. Like MRTD, it is a measure of the performance of infrared cameras.
  
  However, MDTD is a measure of visibility, not resolvability.
  
  Section::::Minimum detectable temperature difference.:Manual test.
   Section::::Technical difficulties.
  
  Section::::Technical difficulties.:Dissolved gases.
  
presuppositions: If water and air are the same temperature then it should not feel colder being in cold water than being surrounded by cold air.  Water and air of the same temperature should feel the same on skin.
corrections: Water has a much higher thermal conductivity than air, so it will transfer heat or cold through it faster. Skin does not feel temperature, skin senses the rate of energy transfer.
raw_presuppositions: If water and air are the same temperature then it should not feel colder being in cold water than being surrounded by cold air.  Water and air of the same temperature should feel the same on skin. If water and air are the same temperature then they should feel the same.
raw_corrections: Water has a much higher thermal conductivity than air, so it will transfer heat or cold through it faster. Skin does not feel temperature, skin senses the rate of energy transfer. Water has a much higher thermal conductivity than air, so it will transfer heat or cold through it faster.