How Thermal Energy is Measured
Thermal energy is the total kinetic energy of a material. Kinetic energy is the energy of moving objects. Please point out that kinetic energy does not make things move, instead, it is the energy of things that are in motion.
Heat is the transfer of thermal energy from one object to another. Heat is ALWAYS transferred from an object with the higher temperature to an object with the lower temperature.
When you touch an ice cube, it feels cold because heat moves from your warm fingers to the cold ice cube. The reverse is true when you touch something that is at a higher temperature than your fingers.
Temperature is a measure of the average kinetic energy of all the particles making up an object.
When heat is added to an object there is an increase in the average kinetic energy of the particles, so there is a rise in the temperature of the object. Likewise, when heat is lost by an object the average kinetic energy of its particles decreases and the temperature of the object decreases.
Temperature, therefore, is a measure of how hot or cold an object is. If you dip your fingers into a bowl of warm water then dip them in icy water, you can determine that bowl of water has a greater temperature than the other. But you cannot determine the difference in degrees of the two water samples.
While your body is sensitive to differences in hotness and coldness of an object, it can be deceived when different materials are used. For example, a rug laying on a tile floor has the same temperature as the floor. But, the tile floor feels cooler to your bare feet than does the rug. This is because the tile floor is a better conductor of heat than is the rug.
Think About It!
1. Heat is easily transferred through good conductors.
2. Poor conductors of heat are call insulators.
3. Your skin feels cold when it looses heat.
4. When standing on the tile, your feet feel cold, thus heat from your skin is being transferred to the tile.
5. When standing on the rug, your feet do not feel cold, thus heat is not being transferred or is transferred at such a slow rate it is not noticeable.
6. The tile is a good conductor of heat and the rug is a poor conductor of heat. Thus, the rug is an insulator.
A thermometer is an instrument used to measure temperature in specific degrees. Many types of thermometers are used today. One type has a small diameter tube that opens into a liquid-filled bulb. At one time the liquid in most thermometers was mercury. But it is now known that mercury is toxic (poisonous), so other liquids are being used. Today a safe vegetable oil type liquid and dye mixture is being used in many thermometers.
In a liquid thermometer, when the liquid in the bulb is heated its particles move faster and move farther apart. The heated liquid expands rising in the tube. The opposite happens when the liquid is cooled. The particles move more slowly and get closer together and the liquid’s height in the tube drops. In order to measure changes in the liquid, a scale is printed along the tube.
The two commonly used thermometer scales are Fahrenheit and Celsius. The Fahrenheit scale is named after the German scientist Daniel Gabriel Fahrenheit (1686-1736). The unit of temperature on the Fahrenheit scale is the degree Fahrenheit, oF. The Celsius scale is named after the Swedish scientist Anders Celsius (1701-1744) and the unit of temperature is the degree Celsius,oC. These scales have the same two reference points, the freezing and boiling points of water, but differ in the values given to each. On the Fahrenheit scale, water freezes at 32 oF and boils at 212oF at sea level. On the Celsius scale, which is used in most scientific work, water freezes at 100oC and boils at 100oC at sea level.
Activity: Hot or Cold?
Purpose To demonstrate how accurate touch is in measuring temperature.
Materials
2 spoons of equal size, 1-metal, 1-plastic
Procedure
1. Place both spoons on a table for 5 minutes or more.
2. Hold the bottom of the metal spoon’s bowl against your cheek. Note how hot or cold the spoons feels.
3. Repeat step 2 using the plastic spoon.
Results
The metal spoon feels colder than the plastic spoon.
Why?
The temperatures of the metal and plastic spoons are the same. The metal spoon is a better conductor of heat than is the plastic spoon. This means that heat flows more easily through the metal than it does through the plastic. When you touch the spoons, more heat is transferred from your skin to the metal spoon than to the plastic spoon. The metal spoon feels colder because the nerves in your skin send messages to your brain that heat is being lost. Thus, you are aware of the transfer of heat rather than the actual temperature of the spoons.
Celsius Thermometer Reading Exercise
