David King of Christ's College asks :-
If temperature has to do with kinetic energy, why are some strong winds cold?
Erick Brenstrum, a weather forecaster with MetService and the author of "The New Zealand Weather Book", responded.
Molecules in a gas, such as air, are moving very fast in random directions, frequently colliding with each other and any surfaces available. This is known as "brownian motion". The speed of the molecules is around 2000 kilometres per hour, but the path of travel before collision is extremely short.
The air movement known as wind is superimposed on the brownian motion and is typically less than 50kph although it can rise above 200kph in hurricanes and tornados. The temperature of the air depends on the kinetic energy of its molecules which varies as the square of their speeds.
So, the kinetic energy of the air molecules due to the brownian motion is thousands of times greater than the kinetic energy due to the wind and largely determines the temperature of the air. If the air has come from the over the southern ocean it is cold, if from the tropics it is warm. If it goes over a mountain chain, dropping its moisture as rain, the air also heats up on the downwind side.
Aside from the temperature, how warm or cold the air feels to us also depends on several other phenomena. When there is no wind, our bodies are partially insulated by a thin layer of air next to the skin. When the wind picks up, this layer is progressively eroded, exposing us more to the temperature of the surrounding air.
How we experience the air's temperature also depends on the humidity of the air, which is a measure of how much water vapour the air contains. The higher the humidity, the hotter a warm day will seem to us, because our cooling system depends on using body heat to evaporate sweat from the skin's surface. When the humidity is high, water vapour in the air will condense onto our skin, releasing heat into our body, almost as fast as sweat evaporates off our skin, taking heat away.