## Key Idea: Thermal energy is associated with the temperature and the mass of an object and the material of which the object is made.

Students are expected to know that:

1. The temperature, the mass of the object, and the material of which the object is made all affect the thermal energy of the object.
2. Every object, regardless of whether it is a solid, a liquid, or a gas, has some thermal energy even if the object’s temperature is very low.
3. Objects that are made of the same material, have the same mass and are at the same temperature have the same amount of thermal energy.
4. The higher the temperature of an object, the more thermal energy the object has, and the lower the temperature of an object, the less thermal energy the object has.
5. When the thermal energy of an object increases, the temperature of the object increases and when the thermal energy of the object decreases, the temperature of the object decreases (assuming the mass of the object does not change).
6. For objects that are made of the same material and have the same mass, the object with the highest temperature will have the most thermal energy and the object with the lowest temperature will have the least thermal energy.
7. For objects that are made of the same material and have the same mass, the object with the greatest thermal energy has the highest temperature and the object with the least thermal energy has the lowest temperature.
8. For objects that are made of the same material and at the same temperature, the object with the greatest mass will have the most thermal energy and the object with the least mass will have the least thermal energy.
9. For objects that are made of the same material and at the same temperature, the object with the greatest thermal energy has the greatest mass and the object with the least thermal energy has the least mass.
10. Objects that are made of different materials may have different amounts of thermal energy even if they have the same mass and temperature.
11. For objects that are made of the same material and have the same amount of thermal energy, the object with the greatest mass will have the lowest temperature and the object with the least mass will have the highest temperature.
12. For objects that are made of the same material and have the same amount of thermal energy, the object with the highest temperature will have the least mass and the object with the lowest temperature will have the greatest mass.

Boundaries:

1. Students are not expected to know or use the formulas associated with thermal energy, such as 3/2 kT and m(ΔT)Cp. The sub-ideas above describe qualitative relationships.
2. This idea refers to macroscopic objects not individual atoms and molecules.
3. Students are not expected to know the relationship between heat and temperature, that heat capacity is a measure of how much the temperature of an object will increase with the addition of a given amount of thermal energy, or why an object could feel colder than other objects at the same temperature. The idea that how an object feels does not necessarily reflect the temperature of the object is a prerequisite idea.
4. Students are not expected to compare situations where both the mass and the temperature of the objects vary. In assessment items, either the mass or the temperature of the objects will be held constant while the other varies so that both variables will not be changed at the same time.
5. Additionally, students are not expected to compare the thermal energy of objects that are made of different materials, e.g., we will ask students to compare the thermal energy of one apple to the thermal energy of another apple not apples to oranges.
6. In this idea, the temperature changes will be limited to those that do not involve changes of state.
7. Students are not expected to know that absolute zero is the temperature a substance would have if all atomic and molecular motion were to stop.
8. Assessment items will use Fahrenheit as the units of temperature, for example, 80ºF.
9. Students are not expected to know that temperature is not a characteristic property of substances.
10. Note: The students are not expected to know the difference between “weight” and “mass.” The words “weight” or “weigh” are used as substitutes for “mass” in situations where such substitutions do not make any difference.
11. Note: The term “heat” can be used in everyday conversation as a verb or a noun. When heat is used as a verb, the meaning is basically to raise the temperature of an object as in “I heated the water.” When heat is used as a noun, it usually is intended to mean some “energy.” While people often use the term “heat” as a synonym for thermal energy, that use is not scientifically correct. Technically, “heat” is the energy transferred from one system to another (or between a system and its environment) due to a temperature difference between the systems (or between the system and its environment). Thus the term “heat” should be used in a manner similar to the word “work” in that it should only be used to describe the energy transferred into or out of a system, not the energy in a system. Students are not expected to know the proper use of the term heat. To avoid confusion, the everyday use of the “heat” as a noun should be avoided in middle school instruction and beyond. The use of “heat” as a verb does not cause a problem, however.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number
6–8
9–12
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70%

70%

61%

63%

60%

61%

56%

64%

46%

53%

44%

50%

38%

42%

41%

41%

29%

41%

34%

33%