Science Buddies: "Ask an Expert"

Could you please help me get started with researching my science project. Does a fan blowing on your face make you cooler or does it make you think you are cooler. I have tried the internet. I could not find anything.
Thank you for your help
Chris

Your question has aspects of physcology, physiology, and physics.

To understand the physics, try doing some searching for articles on
1) "heat transfer" and then more specifically "convection heat transfer"
2) "Evaporation" and "heat of vaporization"

I'm not sure how to quickly find information on the physiology aspects in a form oriented to understanding your question. The human body blood flow, capillaries, thermal responses, and heat sensory nerves are all involved. You might find some articles by searching for something like "Understanding Wind Chill Factors"; however, these will probably only deal with the very cold part of the physiology. Articles located by searching for wind chill aren't likely to deal with hot conditions when we perspire to cool ourselves and the affect of wind / air movement on this cooling.

As to the physcology aspects, your asking in the wrong forum. I've used evaporation and convection flow designs to move heat from equipment that doesn't have any feelings. I'm sure there are people who would enjoy discussing the philosophical aspects of whether somebody feels more or less cool because of psycological factors than what the actual physiolgic heat transfer would support. In other words, can one's state of mind or other senses be fooled; however, those kinds of testing are probably off limits because of the rules in place for Science Fairs.

You could try a really simple experiment. Doing it in reverse works. That is, if your were an ice cube sitting on the kitchen counter, and there was a fan blowing on you, would you "think" your were warmer, or would you actually be warmer?

This may seem a silly analogy, but it's an experiment you could try. Get two ice cubes that weigh the same. Put them on the kitchen counter - in a shallow container if you don't want water running all over the place. Blow air on one with a fan, - not from a heating source like a hair drier, but just a fan - and keep the breeze from blowing on the other one with a piece of cardboard, or a baking sheet form the cupboard. After you notice the ice cubes have melted some, weigh them, or measure the amount of liquid water each has produced, and see which one is melting the fastest.

It should be the one with the breeze blowing on it. Due to "convective cooling" - heating in this case, a principle mentioned by Craig in the previous response, the ice cube with the breeze will absorb heat more quickly from its environment and melt faster. The same principle applies to your face. The more wind, the faster heat leaves your face, the faster your skin temperature drops, and the colder you "feel". You actually feel what is happening.

This is the concept behind the principal of "wind chill factor". I don't know where you live, but here in Minnesota we are very much aware of the wind chill factor in the winter. Just because the thermometer says its below zero doesn't give you the whole story. You have to worry about how much the wind is blowing. In high winds, the temperature of your exposed skin can drop really fast, causing it to freeze - i.e. get frostbite - pretty quickly. It's all due to convective cooling.

So one other area you might consider researching is "wind chill".

Have fun.

Ed Neu
Buffalo, MN