Angela Shaw, age 14, of Birmingham, Ala., for her question:
WHAT EXACTLY IS HEAT?
Heat is a form of energy. Anything that gives off heat is a source of more heat. on earth, we receive heat from six main sources: the sun, fire, the earth, chemical reactions, friction and nuclear energy.
Man can control some sources of heat, such as fire and nuclear energy, which can be'used to heat buildings and do other work. All heat sources, including those man normally controls, can do great damage if they get out of control.
Heat and energy cannot be seen but the work they do can. The burning of fuel in a jet airplane's engine, for example, creates hot gases which expand and provide the power that moves the plane.
Hot and cold are words that refer to the temperature of an object. Temperature is an indication of an object's internal energy level.
The temperature of an object determines if it will take on more internal energy or lose some when it comes into contact with another object. If a hot rock and a cold rock touch each other, some of the internal energy in the hot rock will pass into the cold rock as heat.
Heat and temperature are not the same thing. Temperature is an indication of the level of internal energy that an object has. Heat is the passage of energy from one object to another.
Heat moves from one object or place to another by either conduction, convection or radiation. Conduction is the movement of heat through a material, such as heat from a burner going through a frying pan. Convection carries heat by circulating a heated material, such as a furnace warming the air around it. Radiation carries heat in the form of waves through space.
Heat is measured in two kinds of units: British thermal units (BTUs) and calories. One BTU is the quantity of heat needed to raise the temperature of one pound of water 1 degree Fahrenheit.
One calorie is the quantity of heat needed to raise the temperature of 1 gram of water 1 degree Celsius. The calories used to measure energy in food are 1,000 times as large as this heat calorie.
The idea that heat is a form of energy was proved during the mid 1800s by Julius Robert von Mayer, a German physician, Hermann von Helmholtz, a German physicist, and James Prescott Joule, a British physicist.
In 1842 Mayer found that people in warm and cold climates needed different amounts of food energy while Helmholtz determined in 1847 that heat is actually a form of energy.
In the late 1840s, Joule outlined the relationship between . mechanical energy and heat energy, calling it the mechanical equivalent of heat.
There are a number of physical changes that occur when there is a change of temperature. Most materials expand in volume when heated and contract when cooled.