Diving Into Pressure and Buoyancy - PDF #200

(grade K-12)
Downloadable pdf, 26 pages, 14 reproducible labs, full teaching notes plus student notes.

Book Cover: Enlarge

sample book cover

Sample Activity: View

Cartesian divers immerse students into deep understandings of floating and sinking, buoyancy, pressure, Archimedes’ principle, displacement, volume, density, weightless suspension, and more. Differentiated instruction accommodates widely divergent student ability levels and flexibly adapts to tight time schedules. You recycle your own soda bottles. We provide glass eyedroppers of appropriate size if you don’t already have your own. (This download is also available in hard copy: select 'get materials' below.)


Your book orders and tax-deductible contributions sustain our non-profit site. Please help us keep on delivering cheap (but priceless!) hands-on learning to the next generation of learners.


  • free activity
  • book content
  • get materials
  • teaching tips
  • objectives
  • standards

Table of Contents for #200 Diving Into Pressure and Buoyancy - PDF:


Meeting the Standards • Scope and Sequence • Teaching Strategies • Materials • Getting Ready

Student Labs and Teaching Notes

  1. Lab A: Can you rescue an eyedropper "diver" from the bottom of a bottle?
  2. Lab B: Can you pick a floating diver from the mouth of a bottle?
  3. Lab C: Can the same diver both sink and swim?
  4. Lab D: Can you sink a diver completely filled with air?
  5. Lab E: Can you launch a rocket diver?
  6. Lab F: Can you make your diver hover weightless at all water depths?
  7. Lab G: Can you make your diver hover weightless without touching the bottle?
  8. Lab H: Who can fine-tune their diver to rise the slowest?
  9. Lab I: Can you control an open diver with your bare hands?
  10. Lab J: Does a diver's hover point change when you cap the bottle?
  11. Lab K: Is your diver a temperature sensor?
  12. Lab L: Can you turn a test tube into a diver?
  13. Lab M: Can you turn a fast-food condiment packet into an open-air diver?
  14. Lab N: What else makes you curious?
  15. Student Notes

  16. page 23: displacement • buoyancy • Archimedes' principle • weight
  17. page 24: pressure vs. depth • compressibility • volume • mass • density • states of buoyancy • action/reaction
  18. page 25: weightless hover point • cohesion • adhesion • pressure vs. volume • temperature vs. volume
  19. page 26: summary -- nine Cartesian diver variables

Learning System Cutouts

depth gauges

Complete Master List for #200 Diving Into Pressure and Buoyancy - PDF:

Key: (1st/2nd/3rd) denote needed quantities: (1st) enough for 1 student doing all activities; (2nd) for 30 students working in self-paced pairs; (3rd) for 30 students working in pairs on the same lesson. Starred* items may be purchased below.

  1. 1/15/15: 2-liter plastic soda bottles with tight-fitting lids (clean, labels removed)
  2. 1/1/1: water source
  3. * 1/15/15: glass eyedroppers, available from TOPS (see Notes A1 for specifications)
  4. 0.5/8/8: feet waxed dental floss
  5. 1/2/8: scissors
  6. * 3/17/20: straight plastic straws (avoid very wide ones)
  7. 1/15/15: towels, rags, or sponges to wipe up spills
  8. 1/2/4: paper punch tools
  9. 1.1/17/17: meters string (heavier than kite string and lighter than cord)
  10. * 3/30/45: craft sticks or tongue depressors

  11. * 1/5/15: thick rubber bands (not likely to break when pulled hard)
  12. * 1/5/15: thin rubber bands
  13. * 1/15/15: inches clear tape
  14. 1/1/1: access to cool water (from a tap or refrigerator)
  15. * 1/8/15: test tubes
  16. 1/5/15: deep glasses or tall jars
  17. 1/5/15: tubs or trays to catch water overflow
  18. 1/7/17: condiment packets (fast-food type) that float in water
  19. * 1/15/15: pinches modeling clay (oil-based, waterproof)
  20. 1/15/15: staples

  21. * 1/2/8: boxes of paper clips

Convenient Shopping:

Diving Into Pressure and Buoyancy - Printed Copy

26-page printed copy in a friction binder

We print instead of you, and pass along the shipping and handling charges.

Clay - modeling

oil-based, non-drying

Sold by the 100 gram stick, about 1/4 cup, in assorted colors (our choice). One stick serves a whole classroom for TOPS applications.

Craft Sticks


This little flat stick that held your childhood popsicle aloft has many constructive lab applications. Needed for #200 Diving into Pressure and Buoyancy.


glass, with rubber bulbs and screw-on plastic bottle top

These have many lab uses. You may purchase them separately here, or with 1/2 ounce dropper bottles (as item #1121).

Separately, these also double as Cartesian Divers in #200 Diving into Pressure & Buoyancy. If you already have droppers, test them in advance to see if they make good 'divers': Remove plastic bottle top, if any. Dropper must float when empty, then sink with a one-squeeze-intake of water. Test that the seal between bulb and barrel is water tight: The empty dropper should float for a day or so in a glass of water, without taking on visible water.

Paper Clips

size #1, steel, box of 100

Paper clips have 1001 uses in TOPS experiments, and science in general. Feel free to use paper clips you already have, but be aware that different brands come in different sizes and weights. In experiments where uniformity is important, don't mix brands.

Rubber Bands - assorted

10 grams each of thin, medium and thick

You get 30 grams of soft, strong, durable rubber bands: thin #16 (about 50), medium #32 (about 20), and heavy-duty #64 (about 10). These sizes are specifically selected to work in most TOPS experiments.

Straws - straight

plastic, thin

Any length straw, between 0.20 and 0.25 inches in diameter is suitable. Grocery stores generally carry straws with flexible "elbows." You can use those if you cut off the bendable section before using.

Tape - clear

3/4 inch x 1000 inch roll

Your standard desk tape with matte write-on surface.

Test Tube - small reusable

9 mL capacity with 13 mm OD and 4 inch (100 mm) length

A tough Pyrex test tube made with rim and thicker glass. Has a white spot for labeling.

Test Tube - medium disposable

19 mL capacity, 16 mm OD, 5 inch (125 mm) length

A lighter weight rimless Pyrex test tube made with thinner glass.

Teaching Tips for #200 Diving Into Pressure and Buoyancy - PDF:


(K-4): Observe changes in a Cartesian diver when you squeeze this bottle. The harder you squeeze, the faster it sinks. Can you turn a packet of salsa into a Cartesian diver?

(5-8): Squeeze a bottle of water with a floating Cartesian diver sealed inside. This mechanical pressure transfers force throughout the water in all directions. Yet only compressible air inside the diver reduces to a smaller volume. Would a test object still dive if it didn't contain a compressible gas?

(9-12): Squeezing a Cartesian diver compresses its widely-spaced gas molecules much more than its closely-spaced liquid molecules. This decrease in the diver's air volume reduces the amount of water it displaces, increases its density, and decreases its buoyancy. How might you use this diver to monitor changing room temperature?

NOTE: We encourage improvisation - it's one of the main goals of our hands-on approach! You and your students might invent a simpler, sturdier or more accurate system; might ask a better question; might design a better extension. Hooray for ingenuity! When this occurs, we'd love to hear about it and share it with other educators. Please send ideas and photos to tops@canby.com.

Lesson by Lesson Objectives for #200 Diving Into Pressure and Buoyancy - PDF:

  1. Lab A: To improvise a "catcher" with which to rescue an eyedropper "diver" from a bottle of water. To practice rescue skills.
  2. Lab B: To complete construction of the diver catcher. To practice "grabbing" a low-floating diver from the mouth of a bottle of water.
  3. Lab C: To adjust the volume of air in an eyedropper so it has positive buoyancy at the top of a bottle of water, and negative buoyancy at the bottom.
  4. To propose an hypothesis to account for this phenomenon.
  5. Lab D: To observe the floating and sinking properties of a Cartesian Diver. To experience the relationship between air volume and pressure.
  6. Lab E: To understand buoyancy in terms of Archimedes' Principle. To understand rocket thrust in terms of Newton's Third Law of action and reaction.
  7. Lab F: To develop a kinesthetic feel for how water pressure increases with depth. To understand that a diver hovers in weightless buoyancy when its average density equals the density of water.
  8. Lab G: To use subtle pressure changes to control a diver that has neutral buoyancy. To discover that a diver's hover point is inherently unstable.
  9. Lab H: To finely adjust air volumes in a Cartesian diver. To win a "slowest-rising-diver" competition.
  10. Lab I: To discover, develop and refine ways to apply hand pressure to an open bottle of water to make a diver sink, float, and hover.
  11. Lab J: To correlate relative up and down changes in a diver's hover point with changes in pressure.
  12. Lab K: To correlate relative up and down changes in a diver's hover point with changes in temperature.
  13. Lab L: To turn a test tube into a Cartesian diver. To understand why it floats and sinks.
  14. Lab M: To invent a Cartesian diver out of unusual materials. To have fun.
  15. Lab N: To do science: wonder, predict, experiment, observe, conclude, then ask more questions.

National Science Education Standards (NRC 1996) for #200 Diving Into Pressure and Buoyancy - PDF:

TEACHING Standards

These 14 TOPS Labs promote excellence in science teaching by these NSES criteria:

Teachers of science...

A: ...plan an inquiry-based science program. (p. 30)

B: ...guide and facilitate learning. (p. 32)

C: ...engage in ongoing assessment of their teaching and of student learning. (p. 37)

D: ...design and manage learning environments that provide students with the time, space, and resources needed for learning science. (p. 43)

CONTENT Standards

These 14 TOPS contain fundamental content as defined by these NSES guidelines (p. 109):

• Represent a central event or phenomenon in the natural world.

• Represent a central scientific idea and organizing principle.

• Have rich explanatory power.

• Guide fruitful investigations.

• Apply to situations and contexts common to everyday experiences.

• Can be linked to meaningful learning experiences.

• Are developmentally appropriate for students at the grade level specified.

Unifying Concepts and Processes

closed systems • open systems • regularities • theories • models • prediction • evidence • observation • explanation • interaction • change • measurement

Science as Inquiry (content standard A)

question • plan • design • investigate • gather data • classify • use technological tools • quantify • analyze • interpret • predict • communicate • reason • logic • evidence • variables • cause and effect

Physical Science (content standard B)

NSES Framework: properties of matter • changing properties • motions • forces Core Inquiries: buoyancy • floating and sinking • pressure • Archimedes' principle • Cartesian divers • fluids • displacement • pressure changes with depth • compressibility • density • volume • temperature • weight • weightless suspension • unstable equilibrium • ideal gas relationships (PV = kT)
Related Explorations: air • water • Boyle's Law • Charles' Law • Newton's 3rd law (action/reaction) • cohesion/adhesion • surface tension

Science and Technology (content standard E)

invention • design • tools