Density Curriculum

Introduction

What Students Need to Know About Matter, Mass, and Volume

Students need to have a deep understanding of matter in order to develop a deep understanding of density concepts. While this module contains some background information about the nature of matter, it is intended primarily in terms of review. The module assumes that students hold the following prerequisite understandings about the nature of matter, and understand the distinction between volume and mass (or at least "weight on Earth").

The Nature of Matter

• Matter is composed of atoms or "particles." (The particles are molecules, elements, atoms, and compounds.) Between particles, there is empty space.
• Matter takes up space (has volume).
• Matter has mass.
• Air (and all gases) are matter.
• Liquids are matter.
• Matter is measurable. (We can measure its volume and mass.)
• Matter exists in different phases.
• Physical changes involve changes in state, shape, etc. (where the actual particles are not changed).
• Chemical changes involve changes in chemical structure.
• Matter is conserved.
• Molecules are not static. The atoms or molecules in solids move, but stay in the same position relative to one another. The atoms or molecules in liquids move around and change position relative to one another while remaining in contact with each other. The molecules in gases spend almost all their time alone. Each molecule zips through empty space until it hits another one. Then they bounce off each other. Gases can expand and contract much more than solids and liquids because they are mostly empty space.
• Heating matter results in greater movement of the molecules.

Mass and Weight

• Mass is the amount of matter that makes up an object. More accurately, it is a measurement of the amount of matter in an object. It is measured in grams. It is also a measurement of what it takes to move an object, its resistance or stubbornness. It is independent of gravity.
• Weight refers to the amount of force gravity exerts on an object. Therefore, the weight of a particular object is different in different gravitational fields. For example, the gravitational force of a given object on the Moon is 1/6th the gravitational force of the same object on the earth. Objects have the same mass (amount of matter) but different weight in different gravitational fields.

Volume

• Volume refers to how much space matter takes up.
• If an object has a regular shape, its volume can be measured using a ruler.
• If an object doesn't have a regular shape it must be measured by water displacement. (You can also measure a regularly shaped object this way, but you don't have to).
• If an object floats, you hold it just under the surface of the water, then measure the amount of water that the object displaces in an overflow container or how many millimeters the water rises in a graduated cylinder.
• If an object sinks, you drop it into the water, then measure the amount of water that the object displaces in an overflow container or how many millimeters the water rises in a graduated cylinder.