What happened to the dog’s water?

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Navigating this Pathway

[stextbox id = “info”] In this pathway, students try to explain what happens when a liquid evaporates. We recommend having students write the driving question, “What happened to the dog’s water?” in their science notebook and/or displaying this question prominently in the classroom throughout the pathway. Using their super strong glasses, students first try to visualize what is happening to the water in a dog’s bowl when left outside on a sunny day. Students then observe and try to explain what happens to a wet handprint on a chalkboard, focusing on where the water goes. Next, students observe a small puddle on a surface that they agree cannot absorb water. Students try to explain what they observe happening to the puddle over several hours. Students then watch a computer simulation that shows what happens at the particle level during evaporation. Finally, using their super strong glasses, students draw once more what they would see happening to the water in the dog’s bowl as it evaporates. These drawings will help the teacher see how students’ thinking has changed over the pathway.
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Connections to Other Pathways

[stextbox id = “info”] This pathway does not depend on students having done other pathways first. However, this pathway does introduce students to the idea that particles are in constant motion, which they can use to explain phenomena in the other pathways.
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Teacher Content Background

[stextbox id = “info”] All matter is made of particles that are too small to see, that are in constant random motion, and that have empty space between them. All of the particles present in one state (liquid water) are present in the other (water vapor). No particles are destroyed and none are added. The particles in a substance, even a solid substance, are always moving. In liquid water, some particles (water molecules) are moving so fast they leave the liquid and enter the gas phase—a process known as evaporation. For example, over time, all of the water molecules in the dog’s bowl eventually enter the gas phase. The water will evaporate faster on a sunny day because the water molecules absorb energy from the Sun and from the bowl, which makes the water molecules move faster. The faster the water molecules move, the more likely they are to leave the liquid and enter the gas phase. NOTE: Some students may use the word “vapor” instead of “gas.” For the purposes of this pathway, the two words can be treated as synonyms. In fact, they may appreciate making the connection between “vapor” and “evaporation.”
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Student Thinking

[stextbox id = “info”] All students are all familiar with water “disappearing” on a sunny day, but this pathway will confront them with the commonly held idea that all of the water soaks into the surface (Osborne & Cosgrove, 1983; Prain, Tytler, & Peterson, 2009; Russell, Harlen, & Watt, 1989; Tytler, 2000; Tytler, Prain, & Peterson, 2007). Many students have this idea even when the surface does not allow absorption. Some students believe that water literally ceases to exist when it evaporates (Lee et al., 1993; Osborne & Cosgrove, 1983; Russell, Harlen, & Watt, 1989; Tytler & Peterson, 2000). In addition, students may use the word “evaporation” but not know about the process. They may use it simply to describe a puddle or any liquid disappearing without understanding how it disappears.
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Student Experiences

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