Essential Science for Teachers: Physical Science
The Particle Nature of Matter: Solids, Liquids, and Gases Interactive Activity: Virtual Particle Lab
Virtual Particle Lab: Compressibility of Air
Air, unlike water, can be compressed. Why?
In Session 2, we introduced the particle model of matter by looking at examples of the behavior of matter on a macroscopic level that were best explained by assuming matter was made of particles. In these “Virtual Particle Labs,” you will manipulate a realistic scientific model of matter as particles in order to build your understandings about how interactions and changes on a microscopic scale relate to the macroscopic scale.
Each time we show a simulation or give you a choice to change something about a simulation, we’ll ask you to predict the result, so you can check your understandings of the macroscopic implications of the microscopic model.
Each Virtual Particle Lab has the following parts:
- Setup: What phenomenon are we looking at?
- Exploring the Model: Predictions are made about the way the model will act.
- The Virtual Lab: Several parameters are changed to experiment with the model.
- Wrap up: What did we learn?
In Session 2, one of the macroscopic behaviors of matter that we looked at as a reason for preferring the particle model to the continuous model was the compressibility of gases. In the Science Studio, we saw that Joana could push the plunger of a closed, air-filled syringe, which indicated that its volume was not constant. Similarly, we saw that David could not do the same with a water-filled syringe, which indicated that its volume is constant. In this lab, you’ll experiment with a realistic model of air and water to better connect the particle model to your intuitive understanding of the real world.
Exploring the Model: Air
Introducing the Model
Below, we show a simulation of air, where the size of the air molecules has been increased and time has been slowed down.
In order to make the particles visible, we illustrate a very small volume — the side of the box is 161 x 10-10 m (or 161 angstroms, 1 angstrom = 10-10 m). For a sense of scale, each side of the box is 1/1000 the diameter of a human hair. At the scale of the simulation, each atom is approximately the correct size, shown as 3 x 10-10 m or 3 angstroms in diameter. This simulation is set up to show what air (a gas) at room temperature would look like.
A particle in this simulation is represented as a small sphere: blue for nitrogen (78% of the particles in air), red for oxygen (21% of the particles in air) and yellow for argon (about 1% of the particles in air). When you start the simulation by clicking “run,” you’ll see an animation in which each increment is 10-14 seconds — the real particles in air move much faster.
One of the most important ideas of the particle model is that particles are in motion. When you run the simulation, which of the following do you think will be true?
C. The particles will move in all directions, and they will continue to move across the entire container.
Virtual Lab: Air
Now we are going to apply a force to the top of the box, compressing it in the same way that Joana pressed the plunger to compress the air in the syringe. You can choose to push with no force, or with one, two, four or eight units of force. The final volume in each case will be shown as a fraction of the original volume. With each compression, the distance between particles will, on average, be smaller.
Doubling the force on a gas results in which of the following?
B. The particles are squeezed together by the force applied by the piston, and the spaces between them get smaller. Doubling the force, however, does not result in halving the volume, because as we squeeze the particles closer together, the repulsive forces between them get stronger and, as a result, we need to push with even greater force to make the volume decrease more. It is for this reason that Joana could not push the plunger of the air-filled syringe beyond a certain point.
Exploring the Model: Water
Now we’ll take a look at a simulation of a liquid. We’ve made the box smaller by a factor of eight, but the particles are still the same size as those in the previous section. (This is why they look bigger.) You can think of this as a simulation of water.
When you see the simulation, which of the following do you think will be true?
A. The particles will move in all directions, but they will stay in about the same position.
In the case of water, what kinds of forces are acting between the particles?
In the case of water, what kinds of forces are acting between the particles?
Virtual Lab: Water
Now we are going to apply a force to the top of the box as if we were pushing a piston down on the liquid. This is equivalent to David squeezing the water-filled syringe in the program. You can choose to push with no force, or with one, two, four or eight units of force. The final volume in each case will be shown as a fraction of the initial volume.
Doubling the force on a liquid results in which of the following?
D. Although the spaces between the particles in a liquid may get slightly smaller, the particles are already “touching” each other. This means that the distance between particles is small enough that the repulsive forces between particles have gotten so strong that typical forces cannot cause them to be squeezed together any more. However, the particles are moving slowly enough so that the attractive forces can still hold them together.’
The forces between any two particles are tiny, but because so many particles make up a macroscopic object (like syringe of water), we cannot overcome their combined force (as David could not compress the water in the syringe).
In this lab, we’ve seen that the space between particles is a result of the battle between particles’ intrinsic motion and the attractive and repulsive forces between them.
Particles in a liquid or solid phase are moving slowly enough so that the attractive forces are able to hold particles next to each other. If the particles are compressed any more, however, (like David squeezing the plunger of the water-filled syringe), the shorter distances between them cause the repulsive forces to take over. When this happens, there is no change in volume on a macroscopic scale.
Particles in a gas phase are moving too rapidly for the attractive forces to hold them together. An outside force (like Joana pushing on the plunger of the air-filled syringe) will squeeze them closer together, but when they get close enough the repulsive forces take over and the gas becomes harder to compress.
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.