question: Why touching wood feels warm but touching metal feels cold?
comment: Metal is a much better conductor of heat. Both the wood and the metal are colder than your skin, but the metal pulls the heat out of your skin faster than the wood does. Your skin can only detect the transfer of heat, not the raw temperature, so it feels colder than the wood.
passages: When the two bodies come in contact, surface deformation may occur on both bodies. This deformation may either be plastic or elastic, depending on the material properties and the contact pressure. When a surface undergoes plastic deformation, contact resistance is lowered, since the deformation causes the actual contact area to increase
  
  Section::::Factors influencing contact conductance.:Surface cleanliness.
  
  The presence of dust particles, acids, etc., can also influence the contact conductance.
  
  Section::::Measurement of thermal contact conductance.
   The thermal contact resistance of certain sandwich kinds of materials that are manufactured by rolling under high temperatures may sometimes be ignored because the decrease in thermal conductivity between them is negligible.
  
  Section::::Factors influencing contact conductance.:Interstitial materials.
   According to the laws of thermodynamics, all particles of matter are in constant random motion as long as the temperature is above absolute zero. Thus the molecules and atoms which make up the human body are vibrating, colliding, and moving. This motion can be detected as temperature; higher temperatures, which represent greater kinetic energy in the particles, feel warm to humans who sense the thermal energy transferring from the object being touched to their nerves. Similarly, when lower temperature objects are touched, the senses perceive the transfer of heat away from the body as feeling cold.
   Polished wood feels cold like metal. Heat emission is so high that it causes melting of metal vessels in which the wood is burnt.
  
  Section::::Uses.
   In the absence of interstitial materials, as in a vacuum, the contact resistance will be much larger, since flow through the intimate contact points is dominant.
  
  Section::::Factors influencing contact conductance.:Surface roughness, waviness and flatness.
   When two solid bodies come in contact, such as A and B in Figure 1, heat flows from the hotter body to the colder body. From experience, the temperature profile along the two bodies varies, approximately, as shown in the figure. A temperature drop is observed at the interface between the two surfaces in contact. This phenomenon is said to be a result of a "thermal contact resistance" existing between the contacting surfaces. Thermal contact resistance is defined as the ratio between this temperature drop and the average heat flow across the interface.
   BULLET::::- Electronic packaging
  
  BULLET::::- Heat sinks
  
  BULLET::::- Brackets
  
  BULLET::::- Industry
  
  BULLET::::- Nuclear reactor cooling
  
  BULLET::::- Gas turbine cooling
  
  BULLET::::- Internal combustion engines
  
  BULLET::::- Heat exchangers
  
  BULLET::::- Thermal insulation
  
  BULLET::::- Flight
  
  BULLET::::- Hypersonic flight vehicles
  
  BULLET::::- Thermal supervision for space vehicles
  
  BULLET::::- Residential/Building Science
  
  BULLET::::- Performance of building envelops
  
  Section::::Factors influencing contact conductance.
  
  Thermal contact conductance is a complicated phenomenon, influenced by many factors. Experience shows that the most important ones are as follows:
  
  Section::::Factors influencing contact conductance.:Contact pressure.
   When selecting a TIM, care must be taken with the values supplied by the manufacturer. Most manufacturers give a value for the thermal conductivity of a material. However, the thermal conductivity does not take into account the interface resistances. Therefore, if a TIM has a high thermal conductivity, it does not necessarily mean that the interface resistance will be low.
   Near room temperature, the resistivity of metals typically increases as temperature is increased, while the resistivity of semiconductors typically decreases as temperature is increased. The resistivity of insulators and electrolytes may increase or decrease depending on the system. For the detailed behavior and explanation, see Electrical resistivity and conductivity.
   Copper has a thermal conductivity of 231 Btu/(hr-ft-F). This is higher than all other metals except silver, a precious metal. Copper has a 60% better thermal conductivity rating than aluminium and a 3,000% better rating than stainless steel.
  
  Further information about the thermal conductivity of selected metals is available.
  
  Section::::Beneficial properties of copper heat exchangers.:Corrosion resistance.
   Durability is the main advantage of metal furniture. For example, not many types of non-metal furniture can remain outside during winter and still look good when spring arrives. If cared for properly, metal furniture can last up to 30 years. Because most metal furniture is treated for rust and heat resistance, it doesn't need much maintenance.
  
  Section::::Types of metals.
  
  Usually metal furniture is made from either steel or aluminum. To tell aluminum from steel, place a magnet on a metal surface and if it is steel it will stick. 
   Section::::Background.
   This table shows the resistivity ("ρ"), conductivity and temperature coefficient of various materials at 20 °C (68 °F, 293 K)
  
  The effective temperature coefficient varies with temperature and purity level of the material. The 20 °C value is only an approximation when used at other temperatures. For example, the coefficient becomes lower at higher temperatures for copper, and the value 0.00427 is commonly specified at .
  
  The extremely low resistivity (high conductivity) of silver is characteristic of metals. George Gamow tidily summed up the nature of the metals' dealings with electrons in his popular science book "One, Two, Three...Infinity" (1947):
   Most metals show more plasticity when hot than when cold. Lead shows sufficient plasticity at room temperature, while cast iron does not possess sufficient plasticity for any forging operation even when hot. This property is of importance in forming, shaping and extruding operations on metals. Most metals are rendered plastic by heating and hence shaped hot.
  
  Section::::Physical mechanisms.:In metals.:Slip systems.
   More technically, the free electron model gives a basic description of electron flow in metals.
  
  Wood is widely regarded as an extremely good insulator, but its resistivity is sensitively dependent on moisture content, with damp wood being a factor of at least worse insulator than oven-dry. In any case, a sufficiently high voltage – such as that in lightning strikes or some high-tension power lines – can lead to insulation breakdown and electrocution risk even with apparently dry wood.
  
  Section::::Temperature dependence.
  
  Section::::Temperature dependence.:Linear approximation.
   Thermal contact conductance is the study of heat conduction between solid bodies in contact. A temperature drop is often observed at the interface between the two surfaces in contact. This phenomenon is said to be a result of a thermal contact resistance existing between the contacting surfaces. Interfacial thermal resistance is a measure of an interface's resistance to thermal flow. This thermal resistance differs from contact resistance, as it exists even at atomically perfect interfaces. Understanding the thermal resistance at the interface between two materials is of primary significance in the study of its thermal properties. Interfaces often contribute significantly to the observed properties of the materials.
   Soft soldering is characterized by having a melting point of the filler metal below approximately , whereas silver soldering and brazing use higher temperatures, typically requiring a flame or carbon arc torch to achieve the melting of the filler. Soft solder filler metals are typically alloys (often containing lead) that have liquidus temperatures below .
   Two additional design factors also influence the thermal/mechanical performance of the thermal design:
  
  BULLET::::1. The method by which the heat sink is mounted on a component or processor. This will be discussed under the section "attachment methods".
  
  BULLET::::2. For each interface between two objects in contact with each other, there will be a temperature drop across the interface. For such composite systems, the temperature drop across the interface may be appreciable. This temperature change may be attributed to what is known as the thermal contact resistance. "Thermal interface materials" (TIM) decrease the thermal contact resistance.
  
  Section::::Engineering applications.:Microprocessor cooling.:Attachment methods.
   "Internal" chills are pieces of metal that are placed inside the molding cavity. When the cavity is filled, part of the chill will melt and ultimately become part of the casting, thus the chill must be the same material as the casting. Note that internal chills will absorb both heat capacity and heat of fusion energy.
   Metal furniture
  
  Metal furniture is a type of furniture that uses metal parts in its construction. There are various types of metal that can be used, such as iron, aluminium, and stainless steel.
  
  Iron and steel products are extensively used in many application, ranging from office furnishings to outdoor settings.
   Section::::Considerations.
  
  When selecting metal furniture, consider coat and finish, ensuring the surface is powder coated—which does not need maintenance—and the finish is not just painted onto the furniture but baked into the metal. Also, consider your climate. For example, if you live in a rainy area, you will want furniture with heavy waterproofing and light enough to carry indoors. For hot climates, consider that aluminum retains heat, so you can not use it until it cools down.
  
  Section::::Misconceptions.
   The highest temperature of the tool can exceed 700 °C and occurs at the rake face whereas the lowest temperature can be 500 °C or lower depending on the tool...
  
  Section::::Energy Considerations.
   Both "resistance" and "resistivity" describe how difficult it is to make electrical current flow through a material, but unlike resistance, resistivity is an "intrinsic property". This means that all pure copper wires (which have not been subjected to distortion of their crystalline structure etc.), irrespective of their shape and size, have the same "resistivity", but a long, thin copper wire has a much larger "resistance" than a thick, short copper wire. Every material has its own characteristic resistivity. For example, rubber has a far larger resistivity than copper.
   The Arctic Silver company was founded by Nevin House in 1999. Headquartered in Visalia, California, USA, House's original product was a custom modified version of HP's Turbocooler heatsink design from servers and workstations. That experience led to research in thermal compounds, and their material composition. House experimented with silver based solutions, and success with improved formulas led to a change in business focus, to thermal interface compounds.
   Properly applied thermal interface materials displace the air that is present in the gaps between the two objects with a material that has a much-higher thermal conductivity. Air has a thermal conductivity of 0.022 W/m•K while TIMs have conductivities of 0.3 W/m•K and higher.
  
raw_presuppositions: Touching wood feels warm.
raw_corrections: Wood just doesn't pull the heat out of your skin as much as metal does. 