Temperature is a measure of how much heat something contains. The English measure of temperature is in degrees Fahrenheit. The SI (metric) unit for measuring temperature is degrees Celsius. Hot is when heat is present. Cold occurs when heat is lacking. All substances do not gain or lose heat at the same rate. The amount of heat gained or lost by a substance is determined by three factors: 1. the kind of substance 2. the amount (mass) of the substance 3. the temperature change that takes place. The quantity of heat required to raise the temperature of 1 gram of any substance by 1 degree Celsius is referred to as the specific heat of a substance.

Temperature changes create changes in the phase of matter from solid to liquid to gas. Temperature changes are arrested in a substance until all the substance has changed phase. If heat is added to a block of ice, for example, the ice will not rise above freezing (zero Celsius) until all the ice has become a liquid. If heat is applied to liquid water, the temperature of the water will not rise above 100 degrees Celsius until all the water has become water vapor.

Each kilogram of a pure substance requires a certain amount of heat to melt completely. This amount is called the heat of fusion. Each kilogram of a pure substance requires a certain amount of heat to become a gas. This amount of heat is called the heat of vaporization. When water, for example, goes from a vapor to a liquid it releases the heat of vaporization. This extra heat from condensation is a major cause of severe thunderstorms and tornados. The scientific definition for heat is a form of energy transferred because of temperature difference. Therefore, heat always moves from a hot substance to a less hot substance. This energy is called heat only when it is moving from one substance to another. When this energy is inside of something, it is not called heat; it is called internal energy. Only when it moves is it called heat.

Because heat is energy it is described by the law of conservation of energy. This law states that energy cannot be created or destroyed; it can be changed in form. So when eventually our sun "burns out," all its heat will have become moved into the cold reaches of the universe. Its heat will not disappear, it will have just moved and spread out.

Heat moves in three basic ways. It can move through a material without the material itself moving. This type of heat movement is called conduction. Metals are good conductors of heat. Substances which are poor conductors of heat are called insulators. Heat can also move through a material by actually moving the material. This type of heat movement is called convection. The movement of the materials due to temperature differences are called convection currents. Breezes are caused by convection currents. Land absorbs and loses heat faster than water. As it absorbs heat, the air expands and pushes outward and upward. As it loses heat the air contracts and pushes inward and downward. This is why it is almost always windy in areas where large bodies of water meet a land mass. The third way heat moves is as pure energy that moves through empty space. The heat of the sun travels to earth through empty space. Energy that moves through space, and is not carried by matter, is known as radiation. Light, X-rays, microwaves and heat move as radiation. Heat radiation is called infrared radiation.

A cooling system removes heat from a space. Cooling anything requires that heat be removed from it. A fan, increases the rate of heat radiating from objects. When water evaporates, it absorbs heat. Therefore, the human body is cooled by perspiration which absorbs heat as it vaporizes. In freezers, refrigerators and air conditioners, liquid Freon (dichlorodifluoromethane) is pumped into tubes. In these tubes, Freon absorbs heat and turns into a gas. As it absorbs heat, it creates cool air. The gaseous Freon is then pumped outside of the cooling unit. There it gives off heat to the surrounding air and becomes a liquid again. This is why the back of a refrigerator and the outside part of an air conditioner are always very warm. This is where the heat is given off by the Freon. The Freon is pumped through these systems by an electric motor.

Heat loss is deterred by insulation. Insulating materials have fibers which trap air. Since air is a poor conductor of heat, this helps to prevent rapid heat loss. Fiber glass, double glassed windows with air in between, and down, the fluffy feathers next to the body of birds helps to trap air and insulate against heat loss.

Fahrenheit: Celsius:

water boils 212 degrees water boils 100 degrees

water freezes 32 degrees water freezes 0 degrees

Heat Study Sheet