Navigating this Pathway
[stextbox id = “info”] In this pathway, students try to explain how they are able to smell something from a distance, a phenomenon the vast majority of students are familiar with, whether the aroma of cookies baking or an unseen skunk. (Although, it is estimated that about 1 percent of the population has no sense of smell.) We recommend having students write the driving question, “How can I smell something from across the room?” in their science notebook and/or displaying this question prominently in the classroom throughout the pathway. Students first experience smelling something from a distance and try to explain the phenomenon. Then they collect evidence that air (a gas) is something and that there is empty space between the particles. Next, they observation a simulation that shows what happens at a particle level when a gas is compressed. A second simulation allows them to see what happens at a particle level when a liquid evaporates. Finally, students revisit the question of how they are able to smell something from a distance using their emerging understanding of the particle nature of matter.[/stextbox]
Connections to Other Pathways
[stextbox id = “info”] Answering the driving question for this pathway depends on some understanding of evaporation. Students might benefit from doing the “What happens to the water in a puddle?” pathway first.[/stextbox]
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 (a liquid) are present in the other (a gas). No particles are destroyed and none are added. The particles in a substance, even a solid substance, are always moving. In a liquid, some particles (atoms or molecules) are moving so fast they leave the liquid and enter the gas phase—a process known as evaporation. Over time, all of the atoms or molecules eventually enter the gas phase. The faster the water molecules move, the more likely they are to leave the liquid and enter the gas phase. Once particles enter the gas phase, they continue to move randomly, spreading out from the source. However, if there is an air current, as there almost always is, the current strongly influences the direction in which the particles move. 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.”[/stextbox]
Student Thinking
[stextbox id = “info”] Students are familiar with smelling things from a distance, whether it’s pizza, cookies, or vinegar. However, many students have never thought about how they can smell objects that are not right next to them.[/stextbox]
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Student Experiences
[stextbox id = “info”]- Student Experience 1: What’s That Smell?
Students experience the phenomenon of an odor spreading from a source and try to explain how they can smell something from a distance? - Student Experience 2: Air is Something
Students gather evidence that air is matter and is compressible, suggesting that there is empty space between the air particles. - Student Experience 3: States of Matter Simulation
Students observe what happens at the particle level when a gas is compressed. - Student Experience 4: Evaporation Simulation
Students observe evaporation at the particle level using a computer simulation. - Student Experience 5: Revisiting “What’s That Smell?”
Students again imagine how they can smell something from a distance.