**High School Biology-Chemistry SMILE Meeting
23 September 2003
Notes Prepared by Porter Johnson**

**Therese Donatello [ST Edwards, Elmwood Park] Density
+ Archimedes Principle
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:

- 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?

- 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,
**V**._{water} - Put the body into the cylinder (completely submerged), and re-measure the
volume of the body plus the water:
**V**._{total} -
Subtract to determine the volume of the body,
**V = V**._{total}- V_{water} -
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:

- Determine the mass of the empty graduated cylinder,
**M**._{0} - Add a measured volume of water,
**V**, to the cylinder, and determine the total mass of cylinder plus water:**M**_{total}. - The density of water is
**D**._{water}= M_{water}/ V = [ M_{total }- M_{0}] / V

- We used two steel cylinders, each about
- 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!**

Notes taken by **Ben Stark.**