Density in Relation to Float and Sink

Carolyn C. Roberson-Ellis Morton Career Academy
401 N. Troy
Chicago, Illinois 60624


(Grades 6-8)
1. To create a density column from household liquid solutions.
2. To calculate the density of an object.
3. To determine why objects will float or sink in relation to density.
4. To predict the density of unknown solutions.
5. To introduce Archimedes' Principle.


The following materials are needed for each group of 3-5 students:
wood (small rectangular or baby bottle or olive jar
square shape) graduated cylinder
metal screw or nut balance scale
plastic (small rectangular or ruler (metric)
square shape) large plastic container
corn oil or small aquarium
corn syrup paper or plastic cups
food coloring (for water) small piece of rubber
glycerin aluminum foil


Instructors Preparations and Student Activities:
1. The individual student stations should be set up before students arrive. Put
several drops of food coloring into the aquarium. Use different colors for
each group with matching cups. (optional)

2. Each station or group will have the unknown household solutions within the
cups. Students are given the information in regards to water (density = one
gram/cm3). Pour the unknown solutions into the baby bottle. Students will
observe the various columns formed.

3. One should introduce the concept of density using examples and formula,
density = mass/volume. Review methods of computing volume. One should
include the water displacement method too.

4. Each group should have an object for which to compute the density. For
example, a small piece of wood, plastic, metal screw or nut, and rubber
should be used to determine the density.

5. After computing the density, students are to predict whether or not the
objects will sink or float in regards to density. Water is used as your
medium (1 gram/cm3). Make a graph and place all predictions of the board.

6. After making predictions, students are to drop the objects into the aquarium
to observe whether or not the objects will sink or float. Remove objects
from the aquarium and drop the objects into the baby bottles with the unknown

7. Knowing the densities of the given objects, students are to predict the
density of the unknown solutions. Students will make predictions based upon
where within the jar the objects floated. For example, did the object float
above or below the water? Would the unknown solution's density be higher or
lower than that of the density of a known object (wood, plastic, metal,

8. After making predictions, give students the names and densities of the
unknown solutions. Students can compare their predictions. A graph should
be constructed in regards to Mass versus Volume.

Supplemental Activities:

To introduce Archimedes' Principle, students will construct a displacement
container using a two liter pop bottle. They should cut the top and construct a
spout by cutting the side of the bottle 2cm wide and 6cm to 7cm long. Students
will discover, when objects are put into the water, the water will rise or be
displaced. (Use heavy objects to make observations, for example a can of pop
with a known mass.) Archimedes found that the amount of water displaced is
equal to the mass of the object.

In addition, Archimedes' Principle can be demonstrated by having students
construct a small barge with aluminum foil with measurements about 10 square
centimeters. Have students get as many pennies as possible on their barges.
Afterwards, one should explain Archimedes' Principle in relation to why ships

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