Chapter 10

This chapter indicates one physical phenomenon which is heat. People often feel heat in the nature that they are not surprise any more. When we rub hands on a cold day, we feel warmer. We burn gas under a kettle of water, the kettle gets hot, and the water boils. Electricity runs through coils of wire in a toaster, and they get red-hot. In the glare of the summer sun a sandy beach heats up. However, there is a fundamental question which is what the nature of heat is. The heat is a kind of energy. When being heated, the molecules of substances move with more speed. To summarize, heat in a substance is the energy of the motion of its molecules.

Heat is measured by temperature. The common measuring device is the thermometer. In order to make sense to readers, the book gives some examples ranked from high temperature to low temperature. The surface of the sun is 5500 Celsius. Kitchen range flame is 1700 Celsius. Water boils at the temperature of 100 Celsius. The temperature of human body is 37 Celsius. Ice melts at 0 Celsius. Absolute zero that represents the lowest temperature that matter can theoretically reach is –273 Celsius.

Heat moves in three ways which are conduction, convection, and radiation. Conduction is a method of heat movement in which energy is transferred from molecule to molecule by collision or bombardment. The excellent heat conductivity of metals is due to the fact that the electrons of its atoms can flow along through the metal very rapidly and transfer energy to the atoms in cooler regions. In nonmetals, electron movement is restricted and heat energy is passed stepwise from atom to atom, but the process is much slower than in metals. Different materials vary in their ability to conduct heat. Those conduct heat slowly are called insulators. Clothing, blankets, and some house-insulating materials are effective in preventing the loss of heat Convection is responsible for the currents of heat which circulate hot and cold things and transfer energy from hot things to cold things. The difference between conduction and convection is that conduction happens in one thing, whereas convection occurs between two or more separate things. Radiation is quite different from both of these. The transmitting of radiation does not rely on any substance. Sun heating the earth is an good example of radiation because there is particular nothing to be heated in the space between sun and the earth. The sun is as giant broadcast station that emit many invisible waves which are picked up by earth and converted into the energy of heat.

A discussion of refrigeration belongs in a chapter of heat because to cool something means to subtract heat from it. Basically refrigeration depends on the principle that evaporation is a cooling or heat-removing process. Certain type of vapor is compressed into fluid in the pump which evaporates again and absorbs heat at the same time. The vapor then come back into compressor and is turned into liquid. The cycle is repeated in the refrigerator.
.