1. Baking a potato takes a long time, even in a hot oven, because the inside of a potato warms up very slowly.
e. Why Can a Microwave do this job more efficiently and quicker?
f. What is a potato clock and why does it work?
2. An electric hot water heater takes cold water at its inlet pipe and delivers hot water at its outlet pipe. Between these two pipes is a large water container. Many electric hot water heaters have two separate heating elements: one near the top of the water container and one near the bottom. These elements use a lot of electric power so they don't operate simultaneously. Instead, the top element operates until the water near the top of the hot water heater reaches the desired temperature and then the bottom element operates until the water near the bottom is also at the desired temperature. The water heater then turns itself off and waits until more heating is required.
f. How does "Instant Hot" water in a water cooler work differently?
3. A typical electric oven has two separate heating elements: one on top and one on the bottom. The bottom element is used for baking while the top element is used to broil foods.
e. An oven thermometer can accurately gauge temperatures over 250 degrees. How does it do this when the air temperature where the dial gauge is located is much hotter? Why doesn't this thermometer melt or warp in a hot oven?
f. What is different about bulb thermometer and an oven thermometer? Why couldn't you use a bulb thermometer to cook your turkey on Thanksgiving?
4. Sliding friction is useful for starting fires.
a. If you press a wooden peg against another piece of wood and spin the peg rapidly, it can become hot enough to ignite. The peg produces thermal energy no matter how fast it spins, so why is it important that it spin rapidly?
b. If you strike a piece of flint against a piece of steel, you can shave a red-hot spark off the steel. However, moments later the surface of the steel itself barely feels warm. What happens to the thermal energy in that surface?
c. When you rub a match on a matchbook, it suddenly bursts into flames. The principal source of heat here is a chemical reaction in the match head. What purpose does the initial thermal energy serve in starting this reaction?
d. what is a safety match? How does it work?
e. You might see a "cowboy match" in a movie light a match by rubbing it on the heel of their boot. How does a match light that way?
5. Glass transmits the visible light radiated by the white-hot sun but it absorbs the infrared light radiated by objects near room temperature. This selective absorption and transmission gives rise to the "greenhouse effect."
e. How do these greenhouse gases affect the earth's temperature?
f. What is a cold frame and why do gardeners use them?
6. Your room is particularly cold at night. Here are several things that you decide to do to make your room more comfortable.
f. Before there was electricity there were copper and silver bed warmers. These vented vessels were rubbed and kept in the bed. How did they work?
7. A child's toy oven uses an incandescent light bulb to bake cookies or cakes. It resembles a conventional oven, except that the heating element is simply a 60 W electric light bulb.
c. Some that is not a child's toy is Nitinol. What is that, and how is it affected by temperature that is different from other metals?
f. The oven's door locks when the oven is hot. The lock uses a horizontal bimetallic strip. The lower piece of metal in the strip expands more when heated than the upper piece of metal. Which way does the strip curl when the oven is hot?
8. A duck has a thick layer of fat just beneath its skin. In addition to making the duck more buoyant, this fat helps it stay warm in cold water.
a. Why does the duck have trouble maintaining its body temperature in cold weather?
b. Why does the duck have more trouble staying warm in cold water than in cold air?
c. How does the layer of fat help the duck keep warm?
d. Fat is relatively rigid but is chemically almost indistinguishable from liquid oil. Why wouldn't liquid oil be as effective as semi-rigid fat at keeping the duck warm?
e. Muscle tissue is also relatively rigid, but having an extra layer of muscle wouldn't be as effective at keeping the duck warm as the layer of fat. Why not?
f. The duck's oily feathers also tend to trap air near its skin so that cold water doesn't actually touch the duck's skin. Why does this trapped air help keep the duck warm?
9. Often items can be changed through variances in temperature. There are a variety of methods using temperatures and friction reduction which can be quite useful in assembling or disassembling, especially with metal objects.
a. You can remove a tight-fitting iron ring from around a copper cylinder by carefully heating only the iron ring. Why does this technique work?
b. Even if you can't heat the iron ring without heating the copper cylinder, you can free the ring from the cylinder by putting them both in liquid nitrogen, which has a temperature of -195° C. Why should this technique work?
c. One scheme for making it impossible to remove an aluminum post from a hole in an aluminum plate involves temperature. If you start with a post that is slightly too wide to fit into the aluminum plate and then chill the post in liquid nitrogen, it will shrink enough to fit. When it warms up it will fit so tightly in the hole that nothing can remove it. Why won't heating or cooling the post and plate make it possible to extract the post?
d. If a nut has rusted shut, how could it be loosened to open?
e. If a screw head is stripped, how could you remove the screw from wood? From metal?
f. Why is a new jelly jar harder to open? An old Jelly Jar that has not been opened in a while can also be hard to open. Why are the new and the old jar different in why they are sealed and how could you aid opening the new and the old jar?