Key Idea: Temperature variations in fluids such as air and water lead to currents that circulate the fluid, and this circulation transfers thermal energy from place to place in the fluid.
Students are expected to know that:
- When a region of a fluid (e.g., air or water) is warmer than the fluid around it, it rises, and when a region is cooler than the fluid around it, it sinks.
- If the rising or sinking fluid encounters a boundary that blocks its movement (such as the top or bottom of a container, or the surface of a liquid) the fluid will begin to flow horizontally along the boundary.
- The combination of warmer regions of a fluid rising, cooler regions sinking, and movement along boundaries causes circulation of the materials that make up a fluid.
- The continuous circulation of the material that makes up the fluid creates a current. The current moves fluid from place to place, and in doing so it transfers thermal energy from place to place within the fluid. The movement of a fluid with a lot of thermal energy increases the temperature of the fluid at the place where it moves and the movement of a fluid with little thermal energy decreases the temperature of the fluid at the place where it moves.
Note: This idea addresses the process of convection in general, so examples used for items testing this idea will not necessarily be specific to the earth system.
Boundaries:
- Students are not expected to know how much warmer or colder than the fluid around it a fluid needs to be in order to circulate.
- Students are not expected to know that as the fluid moves, energy is also transferred out of the circulating system by conduction and radiation.
- Students are not expected to know how density differences cause the circulation of fluids as part of this idea.
Item ID Number |
Knowledge Being Assessed | Grades 6–8 |
Grades 9–12 |
Select This Item for My Item Bank |
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50% |
58% | |||
46% |
54% | |||
42% |
46% | |||
39% |
47% | |||
42% |
42% | |||
37% |
46% | |||
38% |
46% | |||
Air moves from place to place, and its thermal energy moves with it. | 37% |
43% | ||
36% |
39% | |||
Ocean currents form when warm water rises and cold water sinks. | 38% |
37% | ||
When cold air comes into contact with warmer air around it, the cold air will sink. | 35% |
39% | ||
32% |
37% | |||
Convection currents can occur in gases and liquids but not in solids. | 33% |
35% | ||
34% |
35% |
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.
Code |
Statement |
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Energy is spontaneously transferred out of hotter regions or objects and into colder ones. |