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This past week it has gotten pretty cold up here in the (somewhat) North. With windchill, temperatures have dropped below zero, and with weather like that it can always be a struggle to stay warm. But with the proper clothing, one can still brave the harsh climate and still have a good time. We might often take it for granted, but how exactly does this insulating process work? Heat travels in three ways: conduction, convection, and radiation. Conduction is simply the transfer of heat by colliding molecules, like when a pan will get heated along its full surface instead of the bottom, and this form of energy transfer is the reason why things like microwave burritos often tell you to wait a few minutes before eating, to let the heat distribute itself evenly. In more conductive objects like metal, it is a good way of transferring heat, but in less conductive things like air (air is, in fact, a poor thermal conductor, which seems counterintuitive), it doesn't exactly do much. Radiation is simply the transfer of heat energy through electromagnetic radiation (primarily thermal, or infrared radiation), such as with sunlight or tungsten light bulbs, and for most common objects it doesn't play a big role in the transfer of heat. In fact, if you wound up stranded in space, one half of you would not freeze as the other side boils, as is popular belief. While space is technically very cold, through radiation along heat leaves your body very slowly. The real issue would be (still) your blood boiling, not due to temperature but due to the vacuum of space, and of course the lack of oxygen. But nonetheless, radiation for cooler objects doesn't transfer heat too well. The real reason why winter is cold is because of convection: the movement of air molecules in our atmosphere, the reason for our weather and the reason why open doors have "drafts". While air is a poor conductor, it convects very well, and with colder air being denser and of a higher pressure, cold air will flow into warmer areas, like when a cold front blows in, or you feel a "blast" of cold from your freezer. So in order to combat this flow of air, we bundle up, putting on layers to protect us from the wind and these currents. However, just one layer to stop the wind won't cut it - the transfer of heat itself will generate convection. The real secret to staying warm is a measure of "dead air", or the pockets of gas within our coats or mittens that are too small to give rise to convection currents but still present as to slow conduction. It's the measure of these microscopic packets of air that allow our clothes to be warm without being unnecessarily expensive. While we can certainly cut out these small pockets of air altogether (certain jackets do), the benefits of using dead air maintain warmth at a lower physical cost, and usually make a coat thicker and more resilient to tears. With that, now you know not only how to stay warm, but how staying warm works. So don't forget to bundle up.
Yesterday I climbed Giant Mountain, one of the 46 Adirondack High Peaks. With a summit elevation of 4,627 feet (1,410 m) Giant is the 12th tallest of the high peaks and with an elevation change of 3000 ft in 3 miles it's also on of the steepest. The journey began at the car near the trail head where I was deciding on footwear. The 2 options were hiking boots (0.92 kg a pair) of Nike frees (.42 kg a pair). The boots would be heavier and require more work to ascend the mountain, but would provide better traction and keep my feet dry. The frees would require less energy but likely slip on everything, provide less support and get my feet drenched within minutes. I chose the boots, so how much more work did I do climbing the mountain? The ideal approach to figuring this out would be to multiply the number of steps that I took while ascending and descending the mountain by the average distance that I lifted my feet with each step; and then multiply that by the force I exerted against the weight of my boots/shoes (work=force*displacement). However I didn't count my steps because counting for 5 hours would have driven me insane and the vertical distance that I lifted my feet varried widely on the diffenrt sorts of terain I encountered. So I'll just use the vertical displacement up the mountain as my displacement. The difference im energy expendature can be found by multiplying the difference in weight of the shoes by the displacement up the mountain. Difference in weight=(.92kg-.42kg)(9.8m/s2)=4.9N Vertical displacement=(3000ft)(1mi/5280ft)(1609m/mi)=914m work=force*displacement Difference in work=(4.9N)(914m)=4497.6J So by choosing the boots I expended about an extra 4500 Joules (about 1070 calories) of energy (but I estimate that in reality It was probably closer to double that). However as we climbed further the trail became covered in snow and ice, making it incredibly wet and slippery, so without the boots I likely would have fallen off the the mountain and gotten frostbite on my feet. In the end think 4500J is a fair tradeoff for not dying.