Density - An Introduction

Therese R. Tobecksen           St. Andrew the Apostle
                               331-155th Place
                               Calumet City IL 60409
                               (708) 862-4143

Objectives:


1.  The student will review the concept of heavy vs. light.
2.  The student will review the concept of sink and float.
3.  The student will conclude that solid objects of the same size and shape can 
    have different weights and therefore different densities.
4.  The student will conclude that liquids and gases can also have different 
    densities.

Materials Needed:

Clear flat pan of water, a variety of objects to investigate the sink and float 
concept, a concrete canoe (or any object that students would predict would not 
float but will), a pan balance, a variety of objects to test the concept of 
heavy vs. light, three like size cubes of aluminum, brass, and steel for each 
group, corn syrup, corn oil, one jar or beaker per group, three small plastic 
cups or containers per group, large jar for "density jar", petri dishes, ball 
bearings, glycerine, small scrap of wood, plastic bingo chip, rubber stopper, 
steel washer, two one liter plastic bottles, mineral oil, paint thinner, 
alcohol, helium balloon 

Strategy:

 1. Ask students to predict if concrete canoe will float.  Test predictions.
 2. Have students test various random objects on a balance to determine heavier 
    and lighter objects.
 3. Have students test objects to see which sink or float.
 4. Show equal sized metal cubes of aluminum, brass, and steel.  Have students 
    make some predictions about their weights.
 5. Let students discover that the metal cubes are not the same weights.
 6. Show two petri dishes, one packed with ball bearings and the second one 
    loosely packed.  Place on overhead and introduce the word "density".
 7. Show bottles of corn oil, corn syrup, and water and invite comments about 
    texture, and thickness of fluids.
 8. In small groups, allow students to pour small pre-measured quantities of
    corn syrup, water, and corn oil to see that each liquid forms a separate
    layer.
 9. Show first wave bottle containing mineral oil and blue colored water.  Have 
    students conclude that the blue water is more dense.
10. Show second wave bottle containing paint thinner and alcohol.  Have students 
    decide which liquid is more dense.
11. Make a density jar.  Into a jar pour corn syrup, glycerine, water, and corn 
    oil.  See at what level steel, a rubber stopper, a plastic bingo chip, and 
    a wood chip will float. 
12. Take out a helium balloon and lead students to conclude that the balloon 
    floats because the helium in the balloon has a lower density that the air 
    in the room.

Performance Assessment:

Show students a glass of ice water.  Ask them if they think that the ice or the 
water has a greater density.