## Key Idea: Energy can be transferred from one system to another (or from a system to its environment) in different ways: by conduction, mechanically, electrically, or by radiation (electromagnetic waves).

Students are expected to know that:

1. Thermal energy can be transferred by conduction when a warmer object (including liquids, like water, and gases, like air) is in contact with a cooler one. [Note: this is not the only way thermal energy can be transferred. See boundary statement 3.]
1. Two objects must be in contact with each other for thermal energy to be transferred by conduction (which is not the case for radiation). This means that the sun does not transfer thermal energy directly to the earth.
2. There must be a temperature difference between the objects in contact for thermal energy to be transferred by conduction. The greater the temperature difference the greater the amount of thermal energy that can be transferred by conduction (assuming the mass or type of material is held constant).
3. The thermal energy transferred by conduction goes from the warmer object to the cooler one.
4. As thermal energy is transferred by conduction the thermal energy (and temperature) of the cooler object will increase and the thermal energy (and temperature) of the warmer object will decrease until the objects are at the same temperature. [This sub-idea assumes that neither object changes state, in which case the temperature of the object would not increase or decrease as the change of state was occurring. Assessment items are limited to contexts in which there is no change of state.]
2. Energy can be transferred mechanically when one object pushes or pulls on another object over a distance.
1. In order for energy to be transferred mechanically there must be a change in position and/or shape (the push or pull must act over a distance).  This energy transfer will stop if the motion/changing of position stops.
2. Energy will be transferred mechanically the entire time the push or pull is acting (in the direction of motion) and energy transfer will stop when the push or pull stops.
3. When two pushes or pulls act over the same distance, the stronger push or pull transfers more energy mechanically than the weaker push or pull.
3. Energy can be transferred electrically when an electrical source, such as a battery or generator, is connected in a complete circuit to an electrical device, such as a light bulb, speaker, heater, or motor.
4. Energy can be transferred by electromagnetic radiation.
1. Electromagnetic radiation is always given off by all objects and energy is transferred when this electromagnetic radiation is absorbed by another object.
2. Electromagnetic radiation can transfer energy through space; therefore, objects do not need to be in contact with each other in order to transfer energy by radiation.
3. The amount of electromagnetic radiation given off by an object can depend on the temperature of the object. The higher the temperature of an object, the more electromagnetic radiation the object gives off.
4. When energy is transferred to an object by radiation, the temperature and thermal energy of the object typically increase.  When energy is transferred from an object by radiation, the temperature and thermal energy of the object typically decrease. [This sub-idea assumes that neither object changes state, in which case the temperature of the object would not increase or decrease. Assessment items are limited to contexts in which there is no change of state.]
5. This is the mechanism by which the sun transfers energy to the earth.
5. Students should know that as energy is transferred from one system to another, energy transformations can also occur.

Boundaries:

1. Examples of mechanical energy transfer that students should be familiar with include the energy transfer that occurs when billiard balls hit each other, when a ball is thrown or kicked, when a baseball or golf ball is hit with a bat or club, when an object is set in motion by a rubber band or spring, or when a bobsled or swing is pushed. Assessment items should use contexts in which it is clear that the object supplying the energy has less energy after the transfer and the object receiving the energy has more energy after the transfer. For example, when a ball is thrown, it may be hard to appreciate that your body is loosing energy. Note that this may also be true for other forms of transfer. For example, it may not be obvious that an object that radiates energy loses energy.
2. Students are not expected to know that conduction occurs through collisions of atoms.
3. Students are not expected to know that convection and diffusion are other ways by which thermal energy is transferred.
4. Although students are expected to know that when energy is transferred, a decrease of energy somewhere is accompanied by an increase in energy somewhere else and vice versa, they are not expected to know that the total amount of energy in the system is conserved.
5. Students are not expected to keep track of how much energy is transferred by each mechanism.
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
Select This Item for My Item Bank

70%

74%

65%

69%

60%

62%

58%

64%

53%

66%

53%

65%

55%

58%

51%

63%

47%

59%

48%

51%

48%

50%

41%

61%

48%

48%

45%

49%

43%

51%

43%

47%

39%

50%

39%

49%

40%

47%

39%

44%

35%

43%

33%

46%

35%

41%

31%

42%

31%

41%

23%

30%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

6–8

9–12

NGM010

Energy can be created (Kruger, 1990; Lovrude, 2004; Papadouris et al., 2008).

50%

40%

EGM035

Springs or other elastic objects have the same amount of elastic energy regardless of how much they are stretched or compressed (AAAS Project 2061, n.d.).

38%

33%

NGM016

When two objects at different temperatures are in contact with each other, thermal energy is transferred from the warmer object to the cooler object and “coldness” or ”cold energy” is transferred from the cooler object to the warmer object (AAAS Project 2061, n.d.).

37%

35%

NGM066

When objects are in contact an equal amount of energy is transferred between them, this causes no change in temperature (AAAS Project 2061, 2017).

34%

37%

NGM057

Energy is not transferred from one object to another unless those objects are in direct contact with each other (AAAS Project 2061, n.d.).

35%

31%

NGM031

Only objects that are glowing can transfer energy in the form of electromagnetic radiation (AAAS Project 2061, n.d.).

31%

28%

NGM056

Electrical sources such as batteries transfer energy all the time, even when there is not a complete circuit (AAAS Project 2061, n.d.).

26%

27%

NGM032

Only hot objects can transfer energy in the form of electromagnetic radiation (AAAS Project 2061, n.d.).

25%

21%

NGM013

Thermal energy will continue to be transferred by conduction even after objects in contact with each other reach the same temperature; the temperature of the object getting warmer will continue to increase and the temperature of the object getting cooler will continue to decrease (Kesidou & Duit, 1993).

23%

21%

NGM015

When a cold and a warm object are placed in contact with each other, the warm object gets colder and the cold object gets warmer because “coldness” is transferred from one object to the other (Brook, Briggs, Bell, & Driver, 1984; Newell & Ross, 1996).

23%

18%

NGM054

Only hot or warm objects transfer thermal energy (AAAS Project 2061, n.d.).

23%

16%

NGM067

Energy is spontaneously transferred out of colder regions or objects and into hotter ones.

19%

16%

NGM036

Only the sun transfers energy in the form of electromagnetic radiation (AAAS Project 2061, n.d.).

11%

11%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.