Let us imagine you have a stainless steel cup of ice cream in the fridge. You opened the fridge; the air inside was cold. You stretched out your hand to pick your favourite ice cream and got a jolt.
"Ouch!"
It was numbingly cold!
By Damianosullivan (Own work) [CC BY-SA 3.0 Source, via Wikimedia Commons
But the fridge and the air inside the refrigerator is at the same temperature. Why did the cup appear colder than the air?
This same experience repeats itself in another instance. An air-conditioned room at 15 degree Celsius (60 °F) feels pleasant. But if you enter into the shower and a 15°C (60 °F) water suddenly splashes on you, you'd probably jump out of the bathroom due to how cold it was.
But a thermometer indicates the two materials are at the same temperature.
The questions are these, how does the metal appear colder than air at the same temperature?
Why did the water appear colder than air when they are both the same temperature?
The old physics is here to the rescue. Again.
The perception of different temperature is dependent on the thermal conductivity of different materials. Or more specifically heat transfer.
Thermal conductivity merely is the capability of a material to conduct heat.
The heat transfer occurs at a higher rate for materials that have a high conductivity, and at a lower rate for material with low thermal conductivity.
Take a look at the different material and its thermal conductivity in the table below.
| Material (@25 °C or 77°F) | Thermal Conductivity in Watts/meter-kelvin, W/(m.K) |
|---|---|
| Acrylic | 0.2 |
| Air | 0.024 |
| Aluminium | 205 |
| Copper | 401 |
| Carbon Steel | 54 |
| Concrete | 1.050 |
| Glass | 1.050 |
| Gold | 310 |
| Nickel | 91 |
| Paper | 0.050 |
| PTFE(Teflon) | 0.250 |
| PVC | 0.190 |
| Silica aerogel | 0.02 |
| Silver | 429 |
| Steel, Carbon 1% | 43 |
| Stainless steel | 16 |
| Water | 0.606 |
| Wood | 0.130 |
The important aspect is the style that heat is absorbed or escapes by your body.
If the temperature of the medium(mostly air, water, etc.) that surrounds a body is lower than your body's temperature, your body will give off heat. Or behave in the reverse direction (absorb heat) if otherwise.
Your body's heat transfer or heat loss is fastest on materials that are good conductors. The amount of heat loss is also determined by the thermal conductivity of the material, the higher it is, the more the heat lost when you touch it.
For instance, a stainless steel spoon and a wooden spoon are both inside the same place at room temperature. The stainless steel spoon will appear colder to touch.
Your hand is warmer than the room temperature, both the metal and wooden spoon conducts heat away from your hand.
The metal spoon will conduct the heat away from your hand faster than the wooden spoon would. And give you the impression that steel spoon is colder than the wooden one.
The same thing happens when you leave both spoons in a piping hot soup. The steel spoon will absorb heat more than the wooden spoon and appear warmer to touch.
The water in the bathroom absorbs more heat away from your body faster than the air. Hence the feeling of it being colder than the air.
References
* Thermal Conductivity
* Thermal Conductivity of Different Materials
* Why does cold metal seem colder than cold air?
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