Unit III: Properties of Matter
Introduction
General Instructional Objectives (and corresponding Specific Learning Outcomes) | Unit Content |
Knows terms
Understands the meaning of terms |
atom, Avogadro’s number, molecule, density, elasticity, buoyant force, plasma, surface tension, capillarity, compound, mixture, antimatter |
Understands scientific concepts | atomic structure, Brownian motion, states of matter, the periodic table, atomic bonding, scaling, crystal structure, Archimedes' Principle, Pascal's Principle, Boyle's Law, Bernoulli's Principle, Hooke’s Law, principle of flotation |
Knows all laboratory procedures
Prepares a plan for an experiment Participates in classroom activities Respects the scientific process Displays a scientific attitude Demonstrates skills in laboratory work |
All content |
Instructional Foci
The next section explores the solid state of matter. This discussion should begin with crystal structure, which is what many solids are made of. Blocks can be purchased which illustrate each of the crystal structures, but too much emphasis should not be placed on this. Styrofoam balls arranged to represent, for example, a crystal of sodium chloride (NaCl) can just as easily be used. Then a discussion of density as related to crystal structure (spacing of the atoms) and mass would be appropriate. Changes in the arrangement and bonding of atoms in a material resulting from a deforming force are know as elasticity. When studying elasticity, Hooke’s law should be demonstrated using springs with varying weights (illustrating that the amount of stretch is proportional to the force applied or weight). This discussion will naturally lead to the discussion of tension and compression. Tension and compression rules can be illustrated using arches and domes in architecture. This is why the Astrodome in Houston does not need any columns to support it. Other examples are the Capitol, Eskimo igloos, Roman aqueducts, and the Jefferson Monument. Finally, there should be a brief discussion of scaling.
The liquid state of matter will be explored in this section. We will begin with a discussion about pressure in a liquid. An illustrative example is swimming under water—as you increase in depth you feel an increase in pressure against your eardrum. In addition, when you try to pick someone or something up under water it seems lighter than when you try to lift it out of the water or above the surface. This is due to buoyant force, which depends on the volume of the displaced object, not the weight of the displaced object. A demonstration for this and Archimedes’ Principle follows: using a beaker full of water immediately next to an empty one being held up by a scale, lower a weight, being held up by a scale, into the beaker of water and watch as the scale attached to the weight decreases as the water pours into the empty beaker, and its weight increases. Notice the initial weight of the scale is equal to the weight of the immersed weight plus the weight of displaced water (Archimedes’ Principle). Then demonstrate and discuss the density effects on submerged objects if the object is (1) denser than the fluid (a penny in water), (2) less dense than the fluid (a piece of styrofoam in water), (3) equal density to the fluid (a fish). This will naturally lead to a discussion about flotation. Talk about canoes or ships that, when weighing more float lower (displace more) in the water than when empty or weighing less (displace less)—a floating object displaces a weight of fluid equal to its own weight. Then discuss Pascal’s Principle, an example of which is an automobile lift. Surface tension and capillarity will be the next topics of study. An excellent example relevant to students’ lives is that of soap weakening the cohesive forces between water molecules, hence reducing surface tension. To illustrate this interaction, mix oil and water in a jar then calculate the time it takes for them to separate. Now add soap to the mixture and re-mix it, calculating the time it takes to separate the oil from the water. It should take much longer with the soap in the mixture since soap breaks the surface tension around each oil (dirt) particle. This is what allows the water to surround the dirt particle and carry it away with rinsing. To illustrate capillarity pass around different diameter test tubes filled with water and not the capillary action in each. Also, dip the tip of a paper towel in water and notice how the water seeps up higher than the water level due to capillary action.
In the final section of this unit we will explore gases
and plasmas. The atmosphere is a relevant illustration of gases doing their
thing. The teacher should also discuss atmospheric pressure, barometers
and Boyle’s Law. An excellent homework exercise for understanding the concept
of pressure is to have the students measure the force or weight of their
car using the area of and pressure in their tires. Give students a large
pieces of graph paper in square centimeters. They should trace the area
of a tire, assuming the other four tires have the same area, and determine
the pressure in the tire (by using a pressure gauge or by assuming the
pressure in the tire is as it should be according to the pressure requirement
of the tire). They should then convert the area traced on the graph paper
from square centimeter to square inches. This number of square inches multiplied
by the pressure of the tire in pounds per square inch will give them the
force or weight of their car! Then discuss the buoyancy of air, which is
just like the buoyancy of water, but in air. Following that should be a
discussion of Bernoulli’s Principle. Only after the students have some
grasp of the this principle should a demonstration of it in action be given.
The demonstration could use a ball tied to a string that is then held under
a steam of running faucet water. Then pull the string away from the steam
and notice the ball stays in the running water. This is, of course, due
to the decrease in pressure from the increase in speed of the water causing
the ball to seek the area of lesser pressure or be pushed from the higher
pressure surrounding air into the lower pressure stream of water. Airplanes,
tornadoes (and torn off roofs), and spin on a tennis ball are also relevant
applications of Bernoulli’s Principle. This section will be concluded with
the discussion of plasma as the fourth state of matter. A discussion of
fluorescent lamps, which use a plasma consisting of low-pressure mercury
vapor, would be appropriate.