Expt 032 -- Cartesian Counters and Messages

Cartesian Counters and Messages. Place several numbered divers together in one bottle, but all with different densities, so they descend in order -- 1, 2, 3... (or with letters so that they spell out a secret message!)

Background

See Diver basics. (BBExperiment 031)

Safety

Use scissors to cut plastic pipets.

Procedure

1. Screw the hex nut securely onto the stem of a graduated plastic pipet. The nut makes its own threads as it goes. With a scissors, cut off the protruding stem of the pipet below the hex nut.

   !!!Click here to See Movie.

2. Make several divers. Write a message, or number the divers in sequence. The order of submerging is adjusted during the filling process below.

   !!!Click here to See Movie. Click |> or <| to step the slides forward or back.

3. Use a beaker or the bottom half of a 2-liter bottle as a flotation testing tank. Place the pipet-nut assembly into the water and observe that it floats rather buoyantly in an upright position with the hex nut acting as ballast. Squeeze out some of the air and draw some water up into the pipet. Now check the buoyancy. If you draw up too much water, the assembly sinks. If this happens, simply lift it out of the water, squeeze out a few drops of water, release the squeeze to allow air back in to replace the water. Using these techniques, adjust the amount of water in the assembly so that it just barely floats (in other words: fine-tune the assembly's density to make it slightly less than that of the water).

   !!!Click here to See Movie.

   !!!Click here to See Picture.

4. Put the message or numbered divers in the same beaker. Adjust the floating levels of the divers to be like stair steps. If the steps are not quite even go back and adjust the amount of air in the divers. The lowest, least buoyant one -- the one with the least air left inside -- is the first to dive (and the last back up when the squeeze is released). The rest dive in order according to their relative buoyancies.

   !!!Click here to See Movie.

5. Transfer all of the divers directly into a 2-liter soda bottle entirely filled with water. Use care not to squeeze any water out of the divers during the transfer. Screw the cap of the bottle tightly closed. Gently squeeze the bottle. Use both hands if necessary. Observe the divers.

   !!!Click here to See Movie.

Questions

1. How can you make two divers (A and B) descend in the same order every time?

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 032 Cartesian Counters and Messages

Watch the movies.

1. Describe the action of the divers.
2. Make some divers with a message at home.
3. Answer the questions.

Curriculum-

This experiment fits in early with discussions of compressibility of gases, liquids, and solids. Students may work with divers to explore the gas laws.

Activity-

Laboratory or Demonstration or Home Experiment

• Divers may be used as a demonstration tool or as an experiment for students. Since all items are household items, the experiment may be a home project.
• This activity is a variation of BBExperiment 031. Use 032, 033, 034, and 035 as alternate activities for groups. Encourage each group of students to choose a different variation. The ones shown are only suggestions to get started. Many variations are possible. The first two are suitable for open divers. The last two require closed divers. Encourage creativity. Display divers at the end.

Time-

• Demonstration:
  • Teacher Preparation: 5-10 minutes
  • Class Time: 5 minutes
• Student Experiment:
  • Teacher Preparation: 5 minutes to collect materials.
  • Class Time: 20 to 30 minutes to build divers, observe and answer questions.

Materials-

• 1 2-L plastic soda bottle
• 5 disposable graduated plastic pipets
• 5 hex nuts (1/4" or of a size that can screw securely onto the stem of the pipet)
• 1 beaker or a plastic soda bottle cut in half
• scissors
• permanent markers

Disposal-

Dispose with ordinary solid trash. The divers may be saved for reuse or sent home with students.

Lab Hints-

See 031 for more tips.

Answers-

Q1. How can you make identical divers descend in the same order every time?

A1. Divers descend when the density of the diver is more than the density of water. Because the diver with the most water (least air) is the most dense, it descends first. The diver with the most air descends last. Once the divers are filled with water and placed in the flask the amount of air does not change.

Key Words 1-

gases, submarine, pressure, volume, Cartesian divers, buoyancy, gases, liquids, compressibility