# Physics 103 Module 3 (Ch. 7)

Chapter 7

60. What is the purpose of the copper or aluminum layer on the bottom of a stainless-steel pot?

Copper or aluminum conducts heat better than steel. The purpose of the copper or aluminum layers on the a steel pot is to make uniform (to spread evenly) the heating from the flames on all the bottom surface.

62. Many tongues have been injured by licking a piece of metal on a very cold day. Why would no harm result if a piece of wood were licked on the same day?

Metal is a better heat conductor than wood and because the heat from the tongue flows much quickly into the metal it can cause local freezing on the tongue.

In addition this happens because the specific heat of the steel  is greater than the specific heat of the wood. (The tongues is harmed because to warm up the steel piece of metal requires a very large quantity of heat).

74. If the composition of the upper atmosphere were changed to permit a greater amount of terrestrial radiation to escape, what effect would this have on Earth’s climate?

The radiation kept into the atmosphere warms up the air and again the land. If greater amount of radiation would escape the general temperature of the atmosphere would drop and the climate would become colder.

78. Porous canvas bags filled with water are used by travelers in hot weather. When the bags are slung on the outside of a fast-moving car, the water inside is cooled considerably. Explain.

Water from inside a  porous canvas bag evaporates. If hung outside of a fast moving car it evaporates faster (because the water vapors in the vicinity of the bag are taken away from the bag vicinity faster by the fast moving air). Evaporation is a process which take away heat from the liquid water. Faster the evaporation is done, faster the water cools down.

104. If you wish to save fuel and you’re going to leave your warm house for a half-hour or so on a very cold day, should you turn your thermostat down a few degrees, turn it off altogether, or let it remain at the room temperature you desire? This question should elicit much discussion!

The heat lost by the home is proportional with the temperature difference between the inside air and the outside air. The cooler the air inside the house the smaller the heat loss. (To warm up after returning home to the same temperature, you will need the same quantity of heat as the house lost during your leaving) It means it is better to turn off altogether the thermostat and let the house coll down as fast as it can (this way the quantity of heat lost by the house will be minimum).

110. Why does spraying fruit trees with water before a frost help protect the fruit from freezing?

As said above water has a very high specific heat comparing with other substances. When you spray with water fruit trees, you give them a protective coating that in order to freeze has to give up very much heat. this protects the fruit from early freeze. Also when the outside water freezes it gives up heat to the inside fruit. A third reason is that after water freezes,  ice is a great insulator and the fruit is protected.