CTS Guide: Water Cycle and Distribution, pp 214-215- Section IV Research Summaries
Clouds and Rain
A study by Phillips (1991) found that some younger students believe that clouds get scrambled and melt and rain occurs when clouds are shaken. Phillips also found some students at the high school level had beliefs similar to younger students. For example, students believed that clouds are formed by boiling vapors from a kettle or the Sun boiling the sea; clouds are mostly smoke; clouds are made of cotton or wool; or clouds are bags of water.
A study by Bar (1986) examined a sample of students ages 5–15 for their conceptions about aspects of the water cycle. He found certain ideas are more prevalent with certain ages. When students ages 5–7 were asked what causes rain, there was little evidence of a relationship between clouds and rain. Several students described clouds as being made of smoke or cotton wool. Of those that did see a link between rain and clouds, clouds were often described as bags of water kept high in the sky; when they collide, they rip open and the water falls out. Students ages 6–8 often described clouds as collecting water from the oceans and then moving to places in the sky above land. At ages 6–9, several students described clouds as being made of water vapor from the Sun heating the sea or water vapor that comes from kettles. At ages 7–10, some students visualize a cloud as a sponge that has drops of water in it. The common idea at ages 9 and 10 is that clouds are made of water evaporated from puddles. At ages 11–15, students begin to describe clouds as made of small drops of water and water vapor that gets cold.
Condensation
Before students can explain the process of condensation, they need to know where the water that condenses comes from (AAAS 2009).
In a study of Israeli children ages 10–14 (Bar and Travis 1991), children were asked what causes water to form on the outside of a container holding ice. The most frequent responses were “the coldness changed into water” or “the cold caused hydrogen and oxygen to change into water.” The researchers concluded that even though students knew that water as a gas (vapor) could be changed back to a liquid, applying that knowledge was difficult for students.
In Osborne and Cosgrove’s (1983) study of New Zealand children’s ideas about change in state, they found that the percentage of students who could explain condensation as resulting from water in the air increased from 10% in children below age 12 to 55% in children ages 12–17. The majority of students gave macroscopic descriptions of condensation with very few mentioning energy and movement of molecules.
Water Distribution and Groundwater
A common misconception of both students and teachers is that water under the ground flows in river-like systems or in large underground lake-like reservoirs. Students who think this sometimes assume that wells will provide water forever because they are filled by underground rivers. The scale of the spaces water fills also varies from micro to macro, with some older students thinking that groundwater fills spaces the size and depth of skyscrapers. (Dickerson et al. 2007).
Feller (2007) identified several common misconceptions about the ocean, including the commonly held idea that the three big oceans are not connected and each acts alone.
The common misconception that groundwater is like an underground lake may come from the level of abstraction that is needed to understand hidden phenomena and processes that take place underground. Research indicates that students’ mental model of groundwater as a static sub-surface lake results from their actual experience with the upper water system (Ben-zvi-Assarf and Orion 2005).
In a study of junior high students’ perceptions of the water cycle, students were asked to agree or disagree with the following statement: Most of the water in our planet is the salty water in the ocean and is not available for humans to use. Of those surveyed, 12.6% agreed, 23.6% were uncertain, and 63.8% disagreed (Ben-zvi- Assarf and Orion 2005).
Evaporation
In a study of water cycle modeling with third graders, several students attributed evaporation to an active process by the Sun to ‘‘attract’’ the water. Another student described the direction of evaporation but noted that ‘‘invisible helium will take the water and bring it up to the clouds and that’s how the clouds get more water.’’ One student noted that ‘‘evaporation goes up to the clouds ... some wind blows that [cloud] over to there.’’ When asked if they think there is water up in the sky all of the time and asked how it gets there, a student replied, “Yes, it evaporates ... which means that little tiny, that you can’t see, water droplets come out of the oceans, lakes, rivers, and ponds, and they go up into the clouds. And, when there is too many water droplets in the clouds, it starts to rain or snow” (Forbes, Zangori, and Schwartz 2015, p. 907).
Research has shown that students seem to go through a series of stages before they fully understand evaporation as a process that converts water to an invisible form. At first they may seem to think that when water evaporates, it simply ceases to exist. In the next stage, they may think it changes location but that it changes into some other form we can perceive, such as fog, steam, or droplets. Fifth grade is about the time that students can accept air as the location of evaporating water if they have had special instruction that targets this idea (AAAS 2009).
Students’ scientific concept of evaporation appears to be dependent on three notions: (1) conservation of matter, (2) the idea of atoms or molecules, and (3) the idea that air contains particles we cannot see. At ages 12–14, students are apt to link these notions (Driver et al. 1994).
Fetherstonhaugh and Bezzi (1992) reported that junior high students had difficulty explaining the process of evaporation in a natural context, and believed that “water vapor is made when the sun is out.”
A study by Barr and Travis (1991) found that students’ understanding of evaporation in a boiling context may precede their understanding of evaporation of water from surfaces. In the sample in that study, 70% of six- to eight-year-old students understood that there was vapor coming out of water when it boiled. They understood that the water was going somewhere as the amount decreased from the container and that the vapor was made of water. However, the same children thought that when a solid, wet object dried, the water simply disappeared or went into the object.