BACKGROUND:
Students will learn in this exercise that all solids
have specific descriptive characteristics. This exercise will focus on one
characteristic, "density," by having the students compare a
variety of heavy (more dense) and light (less dense) rocks.
In rocks of high density, the matter is packed
together more tightly than in rocks of low density. Higher density rocks
will therefore feel heavier than similar-sized rocks of lower density.
PROCEDURE:
- Before lab, prepare sets of objects with differing
densities, one for each student group. The chart below is designed for
eight rocks that you have gathered. If you do not have
the kit, you may use any rocks or objects that the students can hold in
their hands.
- Review the characteristics of the three states of
matter common on Earth. Ask the students what state of matter they
believe rocks belong to. Discuss that solids have a form that does not
change easily.
You may want to discuss with your students that
matter can be changed into different forms. For example, rocks (solid)
can be melted into lava (liquid); ice (solid) can be melted to form
water (liquid), and water can be turned into steam (gas).
- Pick two students to come forward. Give one student
two rocks. Place one rock in each of the student's hands. Ask the
question, "Which one is heavier?" After the student responds
give both rocks to the other student and ask the same question. If they
agree move on to C. If they do not agree, try to break the tie with
another student and then move on.
- Inform the students that one characteristic of
matter is density or how heavy something is. Be sure to reinforce that
in this instance "light" refers to density and not color. Tell
them that they will be looking at rocks and trying to separate them into
two groups, dense and less dense (or heavy and light). Explain that they
will be working with partners just as the two children did in the front
of the classroom.
- Each group will be given a pile of rocks. They are
to divide the rocks into heavy and light piles. If they can't tell, or
the weights feel the same, tell them that they must make a decision. The
students should check all the rocks and help each other. This is the
First Trial.
- After they have separated them into light and heavy
piles, they should separate the heavy pile rocks into lighter and
heaviest. Repeat this for the light pile. This is the Second Trial.
- If time permits and the students are interested,
have them separate the piles once more, for a Third Trial. You will
inevitably see the students arguing over their decisions - just like
real scientists!
The final sorting of the rocks is highly
subjective. The goal of the exercise is not the "correctness"
of the sorting but rather the development of the decision making ability
of the students. Note pyrite is not a rock, but a mineral.
This chart demonstrates the divisions the children
will make in each trial.
|
FIRST TRIAL: |
LIGHT |
HEAVY |
|
SECOND TRIAL: |
LIGHT |
HEAVY |
LIGHT |
HEAVY |
|
THIRD TRIAL: |
L |
H |
L |
H |
L |
H |
L |
H |
|
