Eureka!
By Cynthia House, Thomas Middle School
I sponsor an after school Science Club in a k-5 elementary school. The club is organized into two-week-long sessions, each session
focusing on a specific topic. One of this year’s most successful sessions involved the Archimedes Balance from Educational
Innovations.
For week one I prepared:
1.
2.
3.
4.
two Class Set of Six Archimedes Balances and one Classroom Density Assortment
calculators
answer sheet listing the sample materials and their densities
fill-in table to record findings:
Sample
Description
color
shape
A
Water
Level
with
empty
tube
ml
B
Water
Level
with
sample in
tube
ml
Mass
Subtract A
from B to
get the
mass
*ml = g
D
Water
Level with
no sample
ml
E
Water
level with
the
sample
ml
Volume
Subtract D
from E to
get the
volume
*ml = cm3
Divide the
mass by the
volume to get
the density
g/ cm3
What is the
sample?
Students worked in pairs with first and second grade children teamed with a fourth or fifth grade student. We introduced the topic
with a brief Power Point biography of Archimedes and his accomplishments, focusing on the story of King Hieron’s crown. Then
students practiced determining the density of materials using the Archimedes balance and the samples supplied in the sets. The fillin table helped them remember what measurements to take when, and how to calculate results. I was surprised at how completely
engaged all of the students were, and the accuracy of their results.
To prepare for the second week I assembled the following;
1. control samples: strips of zinc, copper, aluminum, iron, and nickel metal (battery electrodes), and the brass and nylon
cylinders from the Class Set of Six Archimedes Balances Classroom Set and Classroom Density Assortment
2.
samples of unknown composition including coins, screws, bolts and other fasteners, furniture hardware, machine parts,
plumbing fixtures, etc. We had 18 different samples. For very small items, students used enough pieces to obtain accurate
volume and weight measurements, for example, twenty pennies instead of one.
3.
metric rulers, electronic balance, and micrometer
4.
calculators
5.
electrical conductivity tester made from a battery holder, tiny light bulb in a socket, wire, and alligator clips
6.
magnets
7.
graduated cylinders from the Class Set of Six Archimedes Balances Classroom Set
8.
cylinder protectors (see drawing below)
9.
fill-in tables to record findings:
for easy to measure items:
Control
Material
or
Sample
Number
Color
Attracted
by a
magnet?
yes/no
Conducts
electricity?
Yes-strong
Yes- weak
No
Mass
Weigh the
sample on
the balance
g
A
Width
cm
B
Thickness
cm
C
Length
cm
Volume
Area:
Multiply
AxBxC
cm3
Density
Divide the mass
by the volume
to get the density
g/ cm3
for irregularly shaped items:
Control
Material
or
Sample
Number
Color
Attracted
by a
magnet?
yes/no
Conducts
electricity?
Yes-strong
Yes- weak
No
Mass
Weigh the
sample on
the balance
g
D
Water
level with
cylinder
protector
only, no
sample
ml
E
Water level
with
cylinder
protector
and sample
ml
Volume
Subtract D
from E to get
the volume
*ml = cm3
Density
Divide the mass by
the volume to get the
density
g/ cm3
We started the second day by telling the students that the local library needed to obtain samples of items made out of zinc for a
display of the chemical elements. Our Science Club had been contacted to find those zinc items.
Students began by determining the electrical conductivity, magnetic characteristics, and density of the control samples. Since many
of the samples did not fit into the floating tubes provided with the Archimedes Balance sets, and to save time, we determined weight
using an electronic balance. If volume could be easily calculated using measurements with ruler and micrometer we did so.
Having finished characterizing the controls, students now examined the assortment of items of unknown composition, choosing for
themselves which items to investigate. They were cautioned that some items may be lacquered, effecting conductivity results, or
plated, affecting the color. Students determined weight using the electronic balance, and volume using the graduated cylinders. I
thoroughly enjoyed listening to each team’s reasoning for selecting promising candidates. (The zinc sample was post 1982 United
States pennies.)
Cylinder protector:
prevents damage to
the bottom of the
cylinder by heavy or
pointed samples
enables students to
retrieve items without
having to pour out the
water
mechanic’s wire
(or other wire),
an inch or two longer
than the height of the
graduated cylinder
Disk of thin, rigid plastic.
perforated to allow water to
pass through
Diameter slightly less than
the inside diameter of the
graduated cylinder