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Condiment Diver: The World's Simplest Cartesian Diver

Retrieved from the Akron Global Polymer Academy at

Grades: 6-8
Author: Diane Zak
Source: Condiment Diver:, Eric Muller: originally published in the Physics Teacher, May 1996


This activity uses a condiment packet to teach students how fish use their swim bladders to rise and descend in the water. The students will also learn about density, buoyancy, and sinking and floating.


What should the students know as a result of this lesson?

What should the students be able to do as a result of this lesson?


Several squeeze condiment packets (soy sauce, ketchup, mustard, etc.) Many fast food restaurants, such as McDonald's, Arby's, and Burger King, will donate the condiments. * Not all condiments behave the same; therefore it is recommended that they be tested beforehand. Have twice the number of condiment packets that you think you will need.

Clear plastic bottle with tight-fitting lid (1-liter is easier to use for small hands than 2-liter); Wide-mouth bottles are easier to use than regular water bottles in case it is necessary to remove the packet from the bottle.

*Optional: a pair of tweezers to help retrieve the condiment packets from the bottle of water - when the condiment packet needs to be exchanged.
Bucket or large container to empty the bottles of water - when the condiment packet needs to be exchanged.
Bowl of water for testing packets. The teacher may want to put "catch pans" or trays under students' bottles in case of splashes or spills.
Water to fill the plastic bottles: Gallon milk jugs work well
Paper towels



  1. Place a fresh egg in a clear glass of water. It should sink to the bottom. Ask the students how they can get the egg to float without touching the egg. (Gradually add salt. As more salt is added, the egg will begin to float. You can get the egg to remain in the center of the glass before it floats to the top. Sink and float at the same time - neutral buoyancy. By continuing to add salt, the density of the water is increasing. The egg will eventually float on top of the water.)
  2. The density of a fresh egg is greater than that of an older egg because it loses water through the tiny pores in the shell. (So, don't eat an egg that floats in fresh water. It's spoiled.) If you save an egg for several days past the expiration date, you will be able to demonstrate this to the students. Keep checking the egg at home to make sure it is ready to float in time for your demonstration. Place a fresh egg in water - it goes to the bottom and lies on its side;

3-4 days old - stays on the bottom at a 45 degree angle; 10-12 days old - stays on the bottom, but stands straight up; If it floats to the top - it is bad and should not be opened in the house because it will smell.

  1. Show a picture of a submarine or fish and ask the students what they know about its motion, what makes it possible for each to rise and sink in the water.

The swim bladder is filled with gasses which are produced in its blood. When the swim bladder is inflated with these gasses, it increases the fishes' volume decreasing its density, which keeps it from sinking.
Pictures from Holt Science & Technology (2005) Harcourt Education Company: Forces, Motion, and Energy: page 76 & 77

Assessment: Before proceeding, by your questions and their responses, make sure the students' understand what density is and how it affects objects.
Explain how a fish is able to rise and sink in water
Explain how a submarine is able to dive and float in water
Explain how to check if an egg, past its expiration date, is still safe to eat


Before beginning this activity, review safety procedures with students; make sure that students know they are not to taste/eat anything in the science lab.
1. Today we will make a condiment diver. Find out if your condiment packet is a good candidate for a Cartesian diver by dropping the packet in a bowl of water. (See "Content Knowledge" for an explanation of what a Cartesian diver is and how it is made.) The best ones just barely float. *Even though the packets just barely float, some of them still will not sink in the bottle when the bottle is squeezed.
2. Fill the clear plastic bottle with water leaving a small amount of air space. Push the unopened packet into the bottle.
Screw the cap on tight.
3. Squeeze the bottle to make the packet sink, and release to make it rise.
*If the diver does not sink, use another packet. This is where a wide mouth opening is to your advantage since it makes it easier to remove the packet from the bottle. A pair of tweezers also works to help remove the packet from the bottle, but be careful not to puncture the packet.

Assessment: Monitor the students' work to make sure they are following the correct procedures, making observations, and recording data accurately. Redirect their attention to the task, as needed.
Make sure that students are employing safe practices as they conduct the experiment.
Check to see that each member of the group is participating.
Answer students' questions regarding procedures.
1. Name the brands and the contents of the condiment packets that floated.
2. Name the brands and the contents of the condiment packets that did not float.
3. Name the brands and the contents of the condiment packets that worked as Cartesian divers.
4. Are there any similarities with the condiment packets that worked as Cartesian divers.
5. Is there anything inside the packets besides the condiment? (Air)


Students report their findings.
1. What property are we talking about when we are talking about objects floating? (Density which is a comparison between the mass of an object and its volume. Mass is how much stuff is in an object. Volume is how much space an object occupies. Density = mass/volume; Also Buoyant force: Water and air pressure increase the deeper you go. Think of a "Cheer-leader pyramid" - Who has more pressure on them, the person at the top or the cheerleaders on the bottom? (bottom since they have the rest of the cheerleaders on top of them) Since there is more pressure at the bottom of an object in water than at the top, there is an upward force on the object. This force is buoyant force.
If an object in water weighs more than the buoyant force, it will sink. If an object in water weighs the same as the buoyant force, it will float. The steel that is used to build a ship is much heavier and denser than water. So why does it float? The secret is its shape. It is built with a hollow shape which increases it's volume (how much space it takes up), which in turn reduces its density. Therefore it floats.)
2. Why do you think the condiment packet floats? (The density of the packet is less than the density of the water.)
3. What happens to the pressure on the inside of the bottle when you squeeze the bottle? (It increases)
4. When the bottle is squeezed what changes, to the condiment packet, are taking place? (The air in the packet is compressed which changes the volume, which in turn changes the density.)
5. What is affecting the buoyancy of the condiment packet? (Density of the packet/ air inside the packet.)
* Most students are familiar with air being in flotation devices for swimming. Relate this same principle to the condiment packets, which also contain some air.

Assessment: Listen to students' accounts of their findings to judge if their reports are supported by the findings that you observed as experiments were being conducted.
Ascertain students' knowledge of density and buoyancy by asking questions. See above # 1-5
1. Have students create a concept map for buoyant force and density. Include information that shows objects that float on the surface of water, objects that float between the surface and the bottom, and objects that sink to the bottom.
2. Name three things that can be done to change the density of an object. (Change its shape, change its mass or change its volume.)


Swim Like a Fish by Ellen Schecter (1998) Gareth Stevens Publishing Milwaukee, Wisconsin
Who Sank the Boat? By Pamela Allen (book about a cow, donkey, sheep, pig, and a mouse who decide to go for a boat ride.) (1988-1996) Putnam Publishing
Early Step into Reading Boats by Shana Corey (2001) Random House New York
I Love Boats by Flora McDonnell (1995) Candlewick Press Cambridge, Massachusetts

Assessment: Ask questions to ascertain students' understanding of density and buoyancy. Give students 2-3 minutes to complete a brief written summary of the experience. The prompt will be: Imagine that your friend tells you that all heavy objects sink in water. Explain why you agree or disagree with his statement.
2. Make a poster that explains how a life jacket helps a person float. (Most are made of porous material filled with air. The life jacket increases the person's volume which decreases his/her density, therefore the person floats.)


No prerequisites required.

Best Teaching Practices

Alignment with Standards

NGSS Standards:

Common Core Standards:

National Standards:

Ohio Standards:

Content Knowledge

  1. Cut off almost all of the stem (leave about 15mm). Place the hex nut snugly onto the remaining part of the stem.


  1. Fill the pipette about 1/2 -way with water. Place the pipette with the nut into a bottle of water. Screw the lid on tightly, squeeze the bottle.

PictureThe pipette sinks to the bottom of the bottle when it is squeezed, and rises when you release the squeeze. If it doesn't work, adjust the amount of water in the pipette, by adding or subtracting water in the pipette.

Density = mass /volume. A pan balance is the instrument used to find the mass of an object.


Remind students to use materials for the intended purpose; no horseplay in the lab; do not eat or taste anything in the science lab. Be careful about spills; report any spills to the teacher.


Fish use swim bladders to rise and descend in the water.
Submarines use the same principle to rise and descend in the water.
Scuba divers use the principle of buoyancy and density to float and sink in the water
Safety devices for swimming and boating such as life preservers, life raft, "air wings" for the upper arms of young children that cannot swim, etc.


See Learning Cycle, Exploration, Elaboration Assessment, Worksheets

Other Considerations

Grouping Suggestions: Have each student make his/her own Condiment diver, but work in groups of two for the activities

Pacing/Suggested Time: Four class periods - depending on the age of the students and how much detail/involvement you require..

Printable PDF Worksheets (Click on links below to view and print worksheets)

Condiment Worksheet

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