In recognition of your ability
to hum and whistle at the same time, your fellow students have awarded you a
room on the lawn. But only over winter break. After canceling your ski vacation
in Aspen and Vail, you settle in to your new abode and discover that it's
awfully cold. They've turned off all the heat! It's too late to go shopping for
an electric heater tonight, so you prepare for a difficult night's sleep.
Fortunately, the room comes with a fireplace. Unfortunately, the room's previous occupants already burned all the available firewood. That doesn't really present a big problem because you have no homework to do on the room's wooden desk. After throwing the desk onto the sidewalk a couple of times to "soften it up," you take out a match and soon have a nice fire going in the fireplace.
1. You sit in front of the fire, trying to keep warm, and soon find yourself poking at the burning desk with various ordinary objects. You have two old, broken umbrellas--one made entirely of plastic and the other made mostly of metal. While the ends of both umbrellas heat up quickly when you put them in the fire, the handle of the plastic umbrella remains much cooler than that of the metal umbrella. What characteristic of the materials accounts for this difference in behavior, and why does this characteristic differ between plastic and metal?
2. As you sit in front of the fire, you find that your face is becoming unpleasantly hot while the back of your neck remains quite chilly. Explain that odd arrangement of heating.
3. The air in the room is finally beginning to warm up, so you move over to the bed. As you walk by the window and look out into the frigid night, you feel a rush of cold coming at your face. With your hand, you feel a flow of cold air falling toward the floor from the window's surface, but this cold air is not approaching your face. (a) What causes the flow of cold air falling downward from the window, and (b) why does your face feel cold when you look out the window, even though cold air is not hitting your face?
4. Despite the fire, the room air is still cool. As you lie huddled under your blanket, trying to keep warm, you are glad that the blanket consists of tiny fibers that trap air. Assuming that your body is hotter than the room air, (a) why does exposure to the room air make you feel cold, and (b) why does the blanket's structure do such a good job of making you feel less cold?
That
summer job as a video-game tester fell through, so you have decided to
apprentice as a glassblower in one of the boutiques at Kings Dominion. You
spend many a happy hour heating clear and colored glasses with a torch as you
fashion little glass poodles, spaceships, and circus clowns. Not surprisingly,
you have also been learning from painful experience that touching hot glass is
always a bad idea.
5. The torch operates on a mixture of propane and air. What is happening within this mixture that allows the torch to transfer thermal energy as heat to the glass? (Follow energy's movements from the time it arrives at Kings Dominion until it reaches the glass as heat.)
6. When you heat clear glass hot enough to melt it, it emits a dim reddish glow. However, when you heat black glass to the same temperature, it glows bright red. Why does hot black glass emit red light, and why is this light so much brighter than the red light emitted by hot clear glass?
7. Which cools faster to room temperature: hot clear glass or hot black glass? Explain why.
8. Knowing the
temperature of hot glass aids in fabricating those little glass nick-knacks.
Since touching the glass is out of the question, the only ways to judge its
temperature are to look for melting behavior or to study the light emitted by
the glass. What would you look for in this light to know if the glass is hot
enough?