Thermal energy is energy associated with random motion of molecules. It is indicated by temperature, which is the measure of the relative warmth or coolness of an object.
A temperature scale is determined by choosing two reference temperatures and dividing the temperature difference between these two points into a certain number of degrees.
The two reference temperatures used for most common scales are the melting point of ice and the boiling point of water.
- On the Celsius temperature scale, or centigrade scale, the melting point is taken as 0°C and the boiling point as 100°C, with the difference between them being equal to 100 degrees.
- On the Fahrenheit temperature scale, the melting point is taken as 32°F and the boiling point as 212°F, with the difference between them being equal to 180 degrees.
It is important to realize, however, that the temperature of a substance is not a measure of its heat content, but rather, the average kinetic energy of its molecules resulting from their motions.
Below is a 6-ounce cup with hot water and a 12-ounce cup with hot water at the same temperature.
- Do they have the same heat content?
- Do they have the same amount of energy?
Instructions: Click the play button to obtain a magnified view of what is happening. Draw your conclusions, enter your answer in the text field provided, and then click the link below the video to check your answer.
Try This: Measuring Thermal Energy
A six ounce cup and a twelve ounce cup are both filled with 85 degree water.
Conclusion: They do NOT have the same heat content. Since water in the two cups is at the same temperature, the average kinetic energy of the molecules in the cups is the same; however, the 12 ounce cup has twice as many molecules when compared with the 6 ounce cup and thus has the greater total motion or heat energy.