# What is "Cold"?

What makes something (air, beer can, whatever) cold? I’ve always heard it was the slow movement of the molecules of our cold thing. OK, but how does that affect our molecules, slowing them down? If that’s wrong, then fine. Whatever it is that makes something cold, why does it make me cold when I touch it? What are the mechanics of this diffusion?

Wind chill in Albany was about -20 today during the stronger gusts. WTF?

“Cold” doesn’t exist. It is the absence of heat (at absolute zero).

The molecules in your beer can are moving at a slower rate than the ones in your hand. When your hand touches the can, the can’s molecules absorb some of the energy from your hand. Your hand’s molecules slow down slightly, the can’s ones speed up. So the can is taking away your heat, rather than “making you cold”, as such.

Heat, as does anything else, wants to equalize. Nature generally abhorrs vacuums, and tries to fill them. Therefore, things with less heat than their surroundings take heat, and warm things give up heat. You are warm, a can of ale is cold, so the ale gets heat from you. You feel cold. If you were holding a cup of hot coffee, the coffee would give up heat to you, making you warm.

Windchill is a mathematical function of the current temperature and windspeed. It gives a more accurate estimation of how cold it ‘feels’ out than would a straight temperature reading. So if the windchill is -20, it feels 20 degrees below zero outside factoring in the windchill.

From this site ( http://www.nws.noaa.gov/pa/secnews/tip/web-faq.htm#windchill ) we get the formulas:

In US Standard (Fahrenheit/mph):

T(wc) = 0.0817(3.71V[sup]0.5[/sup] + 5.81 -0.25V)(T-91.4) + 91.4

T(wc) is the wind chill, V is the wind speed in statute miles per hour and T is the temperature in degrees Fahrenheit. The formula for windchill, using the Celsius scale is:

T(wc) = 0.045(5.27V[sup]0.5[/sup] + 10.45 - 0.28V)(T - 33) + 33

Again, T(wc) is the wind chill, V is the wind speed in Kilometers per hour, and T is Degrees Celsius.

Two main things that influence how cold something feels: the temperature and the thermal conductivity of the material. If you go outside on a cold day and pick up a piece of wood and a piece of metal, the metal will feel much colder to the touch, even though they’re both at the same temperature. The feeling of cold is associated with transfer of heat from your body to another material.