High School Biology-Chemistry SMILE Meeting
23 September 2003
Notes Prepared by Porter Johnson
Therese Donatello [ST Edwards, Elmwood Park] Density
+ Archimedes Principle
Balance ... Spring scales ... Weights ...
Graduated Cylinders ... Water
Then Terri asked us what information we could obtain about water and
other substances using these materials. [Terri had asked her students to
write a procedure for an experiment of their choosing, using these materials.]
There were various suggestions from SMILE participants, such as these:
Mass ... Volume ... Density ... Length ...
Terri then asked us the following specific questions regarding density
Terri led us through some simple experiments that are designed to help
students take accurate measurements and write proper laboratory reports. [In her
classes she asks students to develop and write a procedure for a laboratory
experiment using part or all of the materials on a list that she
provides.] She began by placing the following equipment and materials on the table:
We then divided into groups, and began developing and writing down a protocol to determine
the density of a body, such as one of the weights in the set.
- If I want to find the density of a body, what equipment or materials should I use?
- How would I find the density using them?
We developed the following successful scheme:
- Use the balance to determine the mass of the body, M.
- Partially fill the graduated cylinder with water to a specified (or measured) volume,
and record that volume, Vwater.
- Put the body into the cylinder (completely submerged), and re-measure the
volume of the body plus the water: Vtotal.
Subtract to determine the volume of the body, V = Vtotal - Vwater
Calculate the density, D = M / V.
Terri then asked us to determine the density of water using these
materials (a simpler question), and we developed the following procedure:
Next Terri asked us to develop an experiment illustrating Archimedes' Principle using the materials
at hand, as listed above. That is, we wish to show that objects fully submerged in water will displace
a weight of water that is equal to the "apparent loss of weight" of the submerged
group discussion, we developed and then followed this procedure:
- Determine the mass of the empty graduated cylinder, M0.
- Add a measured volume of water, V, to the cylinder, and determine the
total mass of cylinder plus water: Mtotal.
- The density of water is Dwater = Mwater / V = [ Mtotal
- M0 ] / V.
We used two steel cylinders, each about 1.5 cm in diameter and
- Fill a plastic cup up to the rim with water.
- Suspend both cylinders from a string, and determine the total mass using a spring scale.
(We got 140 grams).
- Lower the cylinders into the cup until they are completely submerged, and again measure the "apparent mass"
of these objects while they are submerged. (We got 100 grams).
- Collect the water overflowing from
the cup, and determine its mass. [We got about 40 grams.]
- Eureka! Archimedes' principle works!
A wonderful combination of ideas, Terri! Thanks.
Ben Stark [IIT] took the group on a tour of his research
laboratory, to show what tools are used in modern research in molecular biology,
biochemistry, and microbiology. Fascinating, Ben! Schedule of Future Presentations:
Notes taken by Ben Stark.