Essential Science for Teachers: Physical Science
What Is Matter?: Properties and Classification of Matter A Closer Look
A Closer Look
Look for the following topics in the video, indicated by the onscreen icon, and click below to learn more.
Is the Moon Matter?
How Do We Know the Moon is Made of Matter?
In the video we define matter as “having weight and taking up space.” Certainly the Moon seems to take up space — it appears in the sky every night, sometimes blocking our view of the stars, other planets, and even the sun during an eclipse. But how do we know that it has weight?
In the video, we define weight as the measurement of the Earth’s pull on a particular piece of matter. To be more precise, in physics the measure of the amount of stuff in matter is called its mass, which is a quantity independent of whether the matter is on Earth or not. Anything that has mass exerts a pull, or the force we call “gravity,” on other things that have mass. On Earth, we call the measurement of this pull on a particular piece of matter weight.
Since the Moon clearly isn’t on Earth, the question becomes, How do we know if the Moon has mass?
Since antiquity people have observed the moon reliably in the sky, never seeming to fly out of its orbit. This fact provides a clue that there might be some pulling going on. Newton’s third law — for every action, there is an equal and opposite reaction — describes the relationship. If the Earth is pulling the Moon, the Moon is also pulling on the Earth with an equal force and in the opposite direction. So, if the Earth is pulling on the Moon, and the Moon is also pulling back on the Earth, then they both have mass and both take up space, and so by definition are made of matter.
Now that we know that the moon is made of matter and has mass, how could we actually determine how much mass?
You may remember that during the Apollo missions in the 1970s, the Command and Service Module, with one astronaut remaining on board, was in orbit around the Moon for a couple of Earth days. By carefully recording the motion of the CSM as it passed close to the Moon, it was possible to determine the strength of the Moon’s pull on the CSM, which results from its mass. This is the closest we can come to actually weighing the Moon!
It turns out that the Moon contains about 1/80 of the mass of the Earth. If we scale the weight of the Earth to that of an elephant (11,000 pounds), the Moon would weigh as much as the average person (about 140 pounds). Interestingly, the Moon’s matter is almost all solid, with just a small amount of carbon and hydrogen gases, and no liquid.
What is the mystery substance?
The mystery substance that Chris Bash’s class investigates in the video is a variation on what is also sometimes called “oobleck,” after the Dr. Seuss’ book Bartholomew and the Oobleck. It is made up of tiny particles of liquid starch and glue suspended in water. Chemists call this type of mixture a colloid. As Chris’s students discover, this colloid behaves strangely. They describe it as sticky, egg-like, slimy, stringy, droopy, and marshmallow-like. And, as our hosts Sallie and Robin point out, it has properties of both a solid and a liquid. It “holds together” if pressed into a ball, but when left alone, it will take on the shape of its container. Another interesting feature of the mystery substance is that if you try to stir it slowly, it flows easily, like a liquid. However, if you try to stir it quickly or strike it sharply, it resists strongly, like a solid.
Why does the mystery substance behave as it does?
When you stir a liquid, you are applying what a physicist would call a sideways shearing force to the liquid. In response, the liquid shears, or moves out of the way. The behavior of the mystery substance relates to its viscosity, or resistance to flow. Water’s viscosity doesn’t change when you apply a shearing force — but the viscosity of the mystery substance does. Back in the 1700s, Isaac Newton identified the properties of an “ideal” liquid as having a having a consistent viscosity, or resistance to flow, at any given temperature. Water and other liquids that have the properties that Newton identified are called Newtonian fluids. The mystery substance doesn’t act like Newton’s ideal fluid, and is therefore called a non-Newtonian fluid.
Are there other non-Newtonian fluids?
There are many non-Newtonian fluids. They don’t all behave like the mystery substance, and each one is unique in its own way. Ketchup, for example, is a non-Newtonian fluid. Quicksand is a non-Newtonian fluid that acts more like the mystery substance — it gets more viscous when you apply a shearing force. If you ever find yourself sinking in a pool of quicksand (or a vat of cornstarch), try swimming toward the shore very slowly. The slower you move, the less the quicksand or cornstarch will resist your movement.
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.