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Bite-size answers to commonly asked questions from inquiring minds
Did you know?
Antarctica is the coldest place on Earth. In 2009, researchers identified ‘Ridge A’ using satellite technology. At nearly 14,000 metres high, Ridge A has an average winter temperature of -70 degrees Celsuis (-94 F). Brrrrrr. (Source: MSN Science.)
A. Why does a fan keep us cool? Well, an electric fan could actually make the room hotter because the fan’s motor generates heat. Do not leave a fan on in an enclosed room when no one is present – it could only make it warmer and cost you money in electricity consumption. So how does a fan keep us cool?
What a fan does is create a ‘wind chill’ effect when you’re in the room. Moving air cools skin faster than still air. When the weather forecaster talks about wind chill what they are referring to is convection: how the wind (moving air) increases convective heat loss. But what is convection?
Convection occurs when a gas or liquid gets hot – it rises (when you have finished reading this answer you can click here to find out why it rises!). If, for example, you have a mug of hot coffee it will heat a layer of the air directly above. That air then rises because it is hotter than the surrounding air and cold air will fill the empty space left. In turn this air will heat up and rise. One can accelerate the process by blowing. If we didn’t blow on the coffee, it would stay hotter for longer. In effect, convection is a transfer of heat in a gas or liquid - it takes place when heated molecules move from one place to another taking heat with them.
So how does this tie in with a fan making us feel cooler? When we get hot, we perspire (in fact, we sweat to one extent or another pretty much most of the time). By blowing air, the fan increases convective heat loss in us and makes it easier for the air to evaporate our sweat. Liquid evaporating from the skin has a cooling effect. When liquid – in this case sweat – evaporates its molecules turn to vapour (driven by heat) and, in order to escape as vapour, it must take heat energy with it. The heat it takes with it comes from the surface (our skin) from which it has evaporated.
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Source(s): Nakedscientists.com, Howstuffworks.com, Ehow.com, Wisegeek.com, Resources.schoolscience.co.uk, MSN Science