Heat Energy and Heat Transmission
All matter is composed of tiny particles called molecules; most scientists believe that molecules are in a constant state of motion or vibration. They also believe that a body in motion posses’ kinetic energy and that the faster it moves, the move kinetic energy it has. Moving molecules in matter represent kinetic energy that appears in the form of heat. The faster the molecules move, the more kinetic energy or heat there is in a particular substance. When the molecules of a substance slow down, there is less kinetic energy and substance heat.
To make the best possible use of heat, it is important to know how it is transferred from one point to another, and how its movement can be stopped. Heat always flows from a warmer object to a colder object. The transfer rate of heat flow depends upon the temperature difference between objects.
The transmission of heat from one location to an other depends a great deal on the material of the flow path. Heat will flow effectively through solids, liquids and gases. The transmission of heat, however can be achieved only by conduction, convention or radiation.
If one end of a solid metal bar is placed in an open flame. the other end will soon become hot. The process by which hat is transferred from the flame to the cold end of the are is called conduction. For conduction to take place, the heat source must touch the object being heated.
The conduction process applies primarily to heat transmission through solid materials. Metals are bet conductor of heat, whereas non-metals in general are poor conductor or insulator.
Convention is the process of transmitting heat through a fluid such a liquid or gas. When a container of water is placed on a heat source. at first only the water at the very bottom receive heat by conduction through the container. As the bottom layer of water begins to receive heat, it tends to expand somewhat. This condition causes it to become less dense than the cooler water above it. As A result of this condition, warm water begins to rise the surface, which causes heavier cold water to flow down towards the source of heat. The new bottom layer of water will receive heat and rise to the top. The process is repeated over and over again until boiling occurs.
Radiation is a process by which heat is transferred through the motion of waves. A prime example of this is the heat that reaches the earth from the sun. Since the pace between earth and the sun is generally void of molecule except near the earth surface, it heat cannot be transferred by conduction or convention. In effect, heat energy is given off or radiated away from a heat source through infrared rays. Energy of this type moves away from the source in a wave like pattern at the speed of light. An interesting characteristic of radiation is that the air between the heat source and the object. which the waves must pass through, is not heated.