Essential Science for Teachers: Physical Science
Density and Pressure Children’s Ideas About Density and Pressure
Children’s Ideas About Density and Pressure
Below are common ideas children in grades K-6 have about this topic, compiled from research on children’s ideas about science. Consider what evidence might refute this idea, and why a child would be likely to believe this? Once you’ve entered all your answers you can click “printable page” at the bottom of this form to print your answers. You can also click “see possible response” for any question to see one possible response from the series content advisors.
1. An object rises or sinks in water based on its size, weight, and/or shape.
Children aren’t able to directly observe density, the determining “intensive” property of matter that predicts whether something rises or sinks in a fluid. As a result, they rely on their direct experience with the “heaviness” or “bulkiness” of objects, and are often surprised when a large object rises to surface of a liquid and floats. Only objects that are less dense than the fluid they are in will rise and float.
2. Objects with holes in them will always sink, especially once water gets into the holes.
Children may carry this idea from their experiences or memories of having seen boats “spring a leak” and sink. However, objects like the plastic piece with a hole in it in the video may have an average density that is less than the fluid they are in, causing them to rise regardless of whether water gets in the holes.
3. Something floats because it has air in it.
Children often believe that air is the lightest thing there is and, since light things float, anything that contains air will float. Solid objects float because they are less dense than the fluid they are in, not because they contain air.
4. “Pressure” and “force” are the same.
Researchers have found that elementary school students often use these terms interchangeably. As stated in the video, force is the pressure times the area on which the pressure acts. Conversely, pressure is force divided by area. Pressure acts in all directions in a fluid and increases with depth. As the children in the Science Studio swimming pool discovered, the amount of force needed to keep an object underwater is the same at any depth.
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.