Essential Science for Teachers: Physical Science
Density and Pressure Featured Classroom: Tina Grotzer; Arlington, MA
Tina Grotzer; Arlington, MA
“You can’t understand the nature of density without understanding matter. You can’t understand air pressure, and all of the weather-related phenomena around air pressure, without understanding matter. There’s just so much that builds upon it, I would call it one of the most fundamental and generative concepts that we can teach students.”
School at a Glance:
Thompson Elementary School
- Grades: K-5
- Enrollment: 323
- Students per Teacher: 20
7% African American
- Percentage of students receiving free or reduced-price lunch: 23% versus a state average of 29%
Nestled in the heart of East Arlington, Massachusetts, the Thompson School is one of seven elementary schools in the district that science specialist Nadine Solomon visits on a regular basis. In addition to working with the students and modeling lessons for teachers, she occasionally invites science education researchers like Tina Grotzer into classrooms.
Tina has had a long-term relationship with the Arlington Public Schools. She was a teacher in the system for many years, the coordinator of an elementary academic enrichment program, a teacher professional developer, and is now a researcher. As a researcher, Tina developed the Understandings of Consequences Project at Project Zero, at the Harvard Graduate School of Education. The Understandings of Consequences Project addresses the difficulties that students have in understanding cause and effect and how that influences their learning of scientific concepts. The curriculum that grew out of the project focuses particularly on the “non-obvious” causes of macroscopic phenomena, like rising and sinking, by making concepts like density more obvious.
Lesson and Curriculum
Causal Patterns in Density; Understandings of Consequence Project
Lesson at a Glance:
Curriculum: Understandings of Consequence Project, Project Zero, Harvard Graduate School of Education
Topic: Causal Patterns in Density
Prior to this lesson, the students had been working with the Arlington science specialist Nadine Solomon and their teacher Nicole Scalzo in lessons on the nature of matter, states of matter, and what it means in terms of particles for something to be a solid, liquid, or gas.
In this lesson, by using brass and aluminum cylinders and controlling for two variables — mass and volume — Tina made the property of density more obvious to the students. She also began to address the causes for density differences in matter on the particle level, by asking the students to draw their own models for what they think the particles of the two materials would look like under what she called their “microscopic eyes.”
Tina commented, “One of the critical challenges in understanding density is that in addition to particle “crowdedness,” there’s differences between atoms, in terms of their mass. Eventually, the lessons that we’re doing today will lead into lessons on the nature of rising and sinking. What we’ll be trying to get the students to understand at that point is that it’s the relationship between the density of the object and the density of the liquid that accounts for whether it sinks or rises, not just the density of the object itself.”
Session 1 What Is Matter?: Properties and Classification of Matter
What is matter? This question at first seems deceptively simple — matter is all around us. Yet how do we define it? What does a block of cheese have in common with the Moon? What are the characteristics of matter that set it apart from something that is definitely not matter? Matter is one of the big ideas in science. Most areas in physical science can be discussed and explained in terms of matter or energy, and matter is a subject that naturally bridges to the other sciences (chemistry, life, earth science, etc.). In this session, we’ll build a working definition of matter, learn to distinguish between its “accidental” and “essential” properties, and explore it through classification, an activity with a rich history in science.
Session 2 The Particle Nature of Matter: Solids, Liquids, and Gases
What simple idea links together all of chemistry and physics? How can a close study of the macroscopic differences among solids, liquids, and gases support a microscopic model of tiny, discrete, and constantly moving particles? In this session, participants learn how the "particle model" can be turned into a powerful tool for generating predictions about the behavior of matter under a wide range of conditions.
Session 3 Physical Changes and Conservation of Matter
What happens when sugar is dissolved in a glass of water or when a pot of water on the stove boils away? Do things ever really "disappear?" In everyday life, observations that things "disappear" or "appear" seem to contradict one of the fundamental laws of nature: matter can be neither created nor destroyed. In this session, participants learn how the principles of the particle model are consistent with conservation of matter.
Session 4 Chemical Changes and Conservation of Matter
How can the particle model account for what happens when two clear liquids are mixed together and they produce a milky-white solid? What happens when iron rusts? Where do the elements come from? In this session, participants extend the particle model by looking inside the particles, learn about some early chemical pioneers, and in the process discover how the law of conservation of matter applies even at the scale of atoms and molecules.
Session 5 Density and Pressure
What makes a block of wood rise to the surface of a bucket of water? Why do your ears pop when you swim deep underwater? In this session, participants examine density, an essential property of matter. They also look at how particles of matter are in constant motion, which leads to a deeper understanding of fluid pressure. Lastly, the concepts of pressure and density are investigated to explain the macroscopic phenomenon of rising and sinking.
Session 6 Rising and Sinking
Why does a hot air balloon rise into the sky? Why does ice rise in water, when a lump of solid wax will sink in a jar full of molten wax? In this session, participants generalize the model that has been developed about what rises and what sinks, using the idea of balance of forces.
Session 7 Heat and Temperature
What makes the liquid in a thermometer rise or fall in response to temperature? Which contains more heat — a boiling teakettle on the stove or a swimming pool of lukewarm water? In this session, participants focus on the difference between heat and temperature, and examine how both are defined in terms of particles. The particle model is then used to explain a number of everyday phenomena, from why things expand when they are heated to the role that temperature plays in changes of state.
Sessions 8 Extending the Particle Model of Matter
In this session, participants extend their understanding of the particle model to explain additional macroscopic phenomena, including the electrical properties of matter. Participants review the progression of ideas covered in the course and anticipate future developments in the understanding of matter.