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Rochester winters are famous for their snow, and the next one isn’t far off. The more the merrier I say, except when it's that really dense, slushy snow that clogs up your driveway. Unless of course, you're using it to peg some random stranger with. But what if it breaks up like mine always do? Will it still hit the mark? Let's say we have a nice big snowball, separated into three chunks. The dense center has a mass of .02 kg. The next, slightly less dense section has .01 kg, and the outer ring is fluffy snow with .005 kg, for a total of .035 kg. It's thrown from a teenage boy's arm height - let's say 1.2 m - at a small child's head - about .5 m high. The child is 6 m away. The snowball is thrown at exactly 15.88 m/s horizontally so that it may hit the target perfectly. But, after 2 m, .005 kg breaks off, and after another 2m, .01 kg breaks off too. Using conservation of momentum, knowing each piece breaks off at the current speed of the snowball, we find the speed in the x-plane to be 15.88 m/s again! Repeating the same procedure for the next 2 m, we again find that the speed of the snowball hasn’t changed. Thus, the snowball hits its target perfectly, and the scientists involved get a stern talking to from an angry mother. Complete success!
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.
This week has not been the best week for driving. It's been very snowy, and so cold that road salt has been working very poorly, making the roads a slippery mess. Loss of traction can cause serious accidents, so it is best to drive slowly. In the end, it all comes down to friction. Whether you're fishtailing, or stuck in a rut, or have gone into a full on skid, too little friction can cause serious problems. Most commonly people will end up fishtailing more in snowy weather, usually while going around turns. This is characterized by a loss of control in the rear wheels, where they begin to slide as the car continues to turn, even when you try to straighten out. The scary part about sliding is, however, that it is harder to stop than it is to prevent. Once you've started to slide, frictional forces tend to oppose you, and your best bet is to point your front wheels in the direction of the skid and wait until you've regained traction. A similar problem occurs when your drive wheels are spinning out, skidding without a solid connection with the ground. A result of accelerating too fast, it is best remedied by easing up and taking it a bit slower next time. But worst of all is when your front wheels begin to lose control, preventing you from steering and often sending you into a spin. Like with all other winter driving problems, you just have to easy up and "go with the flow", until you can regain control. Proper winter driving requires a gentle touch, and grace under pressure when the inevitable happens. On bad days it is almost unavoidable to have some slipping here and there, but as long as you don't try to overcompensate the issues will stay minor and not wind up getting much, much worse. So drive safe, and try not to panic.