Expt 033 -- Diving Whirligigs and Open Retrievers

A whirligig may be added to a diver. The diver spins gracefully as it sinks, and reverse its spin on the way up. Attach arms and legs to make a diving ballerina! Or, place two divers in the same bottle -- one that barely floats and one that barely sinks, but with mechanisms or devices attached to them that enables the floating one to dive down and retrieve the sunken one off the bottom.

Background

See Diver basics. (031)

Safety

• Use scissors to cut plastic pipets and assorted decorations.
• Use care with the hot glue gun; it may cause burns.

Procedure

Diving Whirligig

1. Add fins and decorations to change the path of the diver and/or give it character. You may attach arms and legs to make a diving ballerina! A bit of hot glue may be used to attach the arms. Use a permanent marker to add a face and other details to the ballerina.
2. Cut a square of plastic about 1 inch or 2.5 cm on a side.
3. Punch a hole in the center of the square. Trim the square into a circle. Make 6-8 evenly spaced cuts around the perimeter of the circle. The cuts should extend approximately 3/4 of the way in to the center hole. Grasp one of the segments, and crimp one corner up and one corner down to make an angled propeller blade. Continue crimping each segment, with corners alternating up-down-up-down to make a full propeller. To get the most out of each propeller blade, make the crimped corners as big as possible, with the folds meeting at the center rim of each blade. (When looked at from the side, each rim should be a nearly straight line angled about 45º from the horizontal.) Push the propeller onto the stem of a graduated pipet. Screw a nut onto the pipet. Cut the stem of the pipet off below the hex nut. The whirligig diver is now ready to use.

   !!!Click here to See Movie.

4. To make a diving ballerina, attach wire arms and legs with a bit of hot glue. Paint details with a permanent marker.
5. When your diver is complete, adjust the water level until the diver barely floats. Work in a large beaker or a 2-liter bottle that has had the top cut off. Place the 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, and let 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 water).

   !!!Click here to See Movie.

   !!!Click here to See Picture.

6. Now the diver spins gracefully as it sinks, and reverses its spin on the way up.

   !!!Click here to See Movie.

Open Retrievers:

Place two divers in the same bottle -- one that barely floats and one that barely sinks, but with mechanisms or devices attached to them that enables the floating one to dive down and retrieve the sunken one off the bottom. Magnets, chewing gum, Velcro, a net, a hook and handle, whatever works!

Instructions for a hook and a hoop style handle follow.

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

1. Cut an 8 cm piece of wire. Bend a wide hook in one end and a narrow hook in the other end. Wrap the narrow hook around the neck of a diver between the bulb and the nut. Use 2 turns to secure it.

   !!!Click here to See Movie.

2. Cut another piece of wire 20 cm long. Make a circle (diameter 3 cm), and twist the ends together. Cut the twisted section at the end. Discard the excess.

   !!!Click here to See Movie.

3. Put a dollop of hot glue on the top(end opposite the nut) of a second diver. Insert the twisted section in the hot glue, and hold a moment to allow the glue to cool and set. Do NOT make a hole in the bulb.

   !!!Click here to See Movie.

4. The hook diver should be adjusted to be just slightly buoyant and the hoop diver should have a little too much water for it to float.
5. When hooked together, however, the entire assembly should just float.

   !!!Click here to See Movie.

6. Fill the hoop diver with water until it just barely sinks. If it is too dense (contains too much water) the hook diver is not able to retrieve it off the bottom! Fill the hook diver with water until it barely floats. If it is too buoyant (contains too little water), it takes an extremely tight squeeze to get it to dive down. Hook the two divers together and be sure that the entire assembly just floats. If not, go back and lower the density on either diver, or perhaps both.
7. Place the divers in a 2-L soda bottle. Screw on the cap. Use the hook diver to fish for the hoop diver. You may need to tip the bottle to set the hook.

   !!!Click here to See Movie.

Questions

1. A student adds wire arms to a diver without adjusting the water inside the diver. Predict what happens when the diver is placed in the water again.
2. A diver is constructed to that it just barely sinks. List as many ways as you can to get the sunken diver to the top of the bottle.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 033 Diving Whirligigs and Open Retrievers

Watch the movies and record your observations.

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 most items are household items, the experiment may be a home project.
• This activity is a variation of Exp 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.

Safety-

• Use scissors for cutting the plastic materials. Open diver projects may be done by students with little supervision.
• Use care with the hot glue gun in preparing closed-system divers or in attaching accessories. The glue gun may cause burns.
• Supervise use of the hot glue gun.

Time-

• Demonstration:
  • Teacher Preparation: 5-??? minutes depending the intricacy of the divers. Divers may be reused indefinitely.
  • Class Time: 10 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
• 2 disposable graduated plastic pipets
• 2 hex nuts (of a size that can screw securely onto the stem of the pipet)
• rigid light weight wire
• colored translucent plastic or vinyl sheets (often used for report covers)
• scissors
• hot glue gun and glue

Disposal-

Retain divers for reuse or send home with students. Dispose with ordinary trash.

Lab Hints-

• See 031 for more tips.
• It is especially important to exclude air from the 2-L bottle with the retrievers. The hoop and hook tend to bounce a bit and air in the bottle exacerbates the problem.
• If the hoop diver proves too difficult or too time-consuming, a much faster, cheaper and easier alternative can be constructed: simply tie one end of a 10-cm string onto the pull tab from an aluminum soda can, and tie the other end onto the plastic ring pried off the top of the 2-L soda bottle neck. The pull tab makes the assembly barely sink, but the plastic ring is buoyant enough to keep itself upright and ready for hooking at the bottom!

Answers-

Q1. A student adds wire arms to a diver without adjusting the water inside the diver. Predict what happens when the diver is placed in the water again.

A1. The diver might sink to the bottom due to the added weight.

Q2. A diver is made so it just barely sinks. List as many ways as you can to get the sunken diver to the top of the bottle.

A2. Students answer this question in a variety of creative and divergent ways. Some answers include: Use a magnet; use a long wire hook; use a straw to blow extra air into the diver; drop in some Alka Seltzer to get some more gas in the diver; add some kind of acid that might eat away at the hex nut; add salt or sugar to increase the density of the surrounding liquid; with the cap off, suck on the bottle to decrease the pressure (or place it in a bell jar and create a vacuum); turn the bottle upside-down!

Key Words 1-

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