Course:     8th grade Physics

Unit Introduction: The Nature of Matter

The Nature of Matter Unit provides students with hands-on and computer-based experiences that will help them modify their existing ideas and construct new ideas about the nature of matter - what makes up the things we see around us.  The first part provides background in mass, volume, and density.  Part 2 begins looking at observable phenomena involving air and develops the particulate theory for gases.  Part 3 expands the theory to include solids and liquids.

Objectives: Students will learn…

 

Properties of Matter

 

Properties of Gases

  1. Gases can only push on objects; they occupy all the space of its container, and have a very small mass.
  2. Gas particles are moving around and spread out randomly, with empty space between them. When the air is compressed or removed the spacing between the gas particles changes.
  3. When the density of a gas changes, the pressure of the gas changes.  At a constant temperature, there are two ways to change the density of a gas: (a) add or remove gas from a container, or (b) compress or expand the gas.

 

Small Particle Theory in Gases

  1. Particles of matter are very, very small compared to normal objects, such as a baseball. Different substances are made of different types of particles.  The particles making up different substances differ in both mass and size.
  2. Gas particles are far apart with empty space between them.
  3. Gas particles move constantly and randomly in all directions, occasionally colliding with each other and the walls.  Gas particles always move faster when the gas is heated, although not all particles move at the same speed.
  4. When gas particles collide with a wall and bounce off, they push on the wall. Pressure is caused by the number of particle collisions per time and the amount of push delivered during each collision.  The type of container, the number of particles, the volume of the container and the temperature of the gas all affect pressure.

Small Particle Theory in Solids and Liquids

  1. The particles of a liquid are much closer together than in gases, in no particular pattern, with empty space between them. Particles of a liquid are moderately attracted to each other, since they are much closer together. Particles of a liquid are constantly in motion, bumping into and sliding past one another. The particles of a liquid move at different speeds. The particles of a liquid always move faster when heated.
  2. The particles of a solid are close together, in a fixed pattern, with empty space between them. Particles of a solid are strongly attracted to each other, resulting in a fixed, unchanged pattern of particles. Particles of a solid are constantly in motion, vibrating in their place within the pattern. The particles of a solid always vibrate faster when heated.
  3. As a solid is heated, the particles of the solid vibrate faster and slightly further apart.  As it continues to be heated, the solid reaches a point where the temperature stops changing for a little bit.  At this point, the heat is being transferred into the energy of the solid particles, and the particles gain enough energy to break the bonds holding them in their fixed pattern. A few particles break free and form a liquid.   This continues until all of the solid particles have gained enough energy to break their bonds and form a liquid. They break free of each other and are able to move around - the solid has become a liquid.  As the liquid is heated, the particles continue to move faster and slightly further apart.  There is a point where the temperature stops rising for a little bit.  At this point, the heat is being transferred into the energy of the liquid particles, and the particles get enough energy to break the bonds holding them close together.  A few particles break free and form a gas - the bubbles in a boiling liquid. This continues until all of the liquid particles have gained enough energy to break their bonds and move freely.