Heat and Temperature Units
Before we talk about temperatures and calories, and the like, let's define a few words that you'll need to know when reading this page. Easier to understand definitions are in parenthesis.
- Energy- Physical quantity that has the capacity to do work.
(The power needed to do work.)
- Heat- Thermal energy that is absorbed, given up, or transferred from one material to another.
(All the energy that is gotten, given, or moved between objects.)
- Thermal Energy- The total potential and kinetic energy associated with the random motion and arrangements of the particles of a material.
(All the combined energies an object has.)
- Potential Energy- Energy due to the position of an object.
(The energy something has just for being somewhere.)
- Kinetic Energy- Energy due to the motion of an object.
(The energy something has just for moving.)
- Temperature- Physical quantity that is proportional to the average kinetic energy of translation of particles in matter.
(The measure of hotness or coldness of something.)
Now that we got all that out of the way, on to the show. We know from experience that heat and temperature are related. They aren't the same however. A burning match has a much higher temperature than a steam radiator, but a match can't keep an entire house warm on a cold winter's night. Suppose we have a large cup filled with boiling water. If we pour some into a smaller cup the temperature will be about the same. However, the water in the large cup could melt more ice than the little cup, because the larger cup has more heat. (Ice absorbs heat as it melts) It is possible for a material to have a high temp but give low heat; low temp, high heat; low temp, low heat; or high temp and high heat.
To measure temperature it is necessary to tell you about something you've probably heard many times, the degree. This unit of temperature difference can't be derived from length, time, mass or any other physical property. There are many physical changes that go along with temperature changes, the length of a solid, the volume of a liquid, the pressure of a gas held at a constant volume, the volume of a gas held at a constant pressure. Some of these properties could be used to make a temp. scale. To make a temperature scale it is necessary to identify a process that occurs without a change of temperature. The temp. at which such a process takes place can be used as a fixed point on a scale. A change of phase of a substance, such as a melting or freezing point, can be used. On the Celsius scale, the freezing point of water is set at 0ƒC and the boiling point at 100ƒC. Now these numbers are all relative. You could create your own temp. scale. You could set the freezing point of orange juice as 1ƒ M (or whatever the first letter of your last name is). The important thing to remember is to keep things in some kind of an order. The Kelvin Scale is another important scale you should know of. This scale was used to come up with a very special number, absolute zero. This is OƒK or -273ƒC. At this temperature all molecular motion is at its minimum. This is as cold as it gets.
There is no instrument that measures the amount of thermal energy a body gives or absorbs. Therefore, quantities of heat must be measured by the effects they produce. For example, the amount of heat given off when a fuel burns can be measured by measuring the temp. change in a known amount of water as the fuel burns. If one piece of coal warms 1 kilogram of water 4ƒC, and another piece warms 1 kilogram of water 8ƒC, the second piece gives out twice as much heat. Now back in the days of old, water was used to define different heat units. The kilocalorie was the amount of heat needed to raise 1 kilogram of water 1C degree. The calorie was the amount of heat needed to raise 1 gram of water 1C degree. But, nowadays we use a much more complicated way. We use joules, 1 calorie = 4.18605 joules and 1 kilocalorie = 4186.05 joules. This way, the size of the calorie is .o1 joules bigger than the old one.