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Mystery Lab / Exhibits & mechanisms

Can a smaller air pocket make the same diver tend to sink?

First change pressure at fixed mass, then mass at fixed pressure. Compare displaced-water mass with the diver’s mass.

Exhibits & mechanisms · two guided observations

An outside pressure change affects the air pocket inside

A Cartesian diver responds to pressure changes made outside a closed water bottle. Our fictional diver has a flexible sealed air pocket and a fixed-volume component. No gas escapes and no water enters. In step one, increasing pressure leaves the diver’s mass unchanged.

The left card is a fixed reference for each step; the right shows your choice. First compare air volumes 5 and 4 cm³ and the up/down directions at two pressures. Then start afresh at 100 kPa and compare only total masses 5.5 and 6.5 g. The arrow combines the effects of upward buoyancy and downward weight: this is the resultant direction. The diver stays at one submerged position; this is not an animated journey.

① Hold mass at 5.5 g and compare 100/125 kPa. ② Hold 100 kPa and total volume 6 cm³, then compare masses 5.5/6.5 g.

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Continue with the story and its records

Explore how the difference you noticed connects with the surviving records of the historical story.

Read about Cartesian divers and their air pockets
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Sources and scope

We consulted the Exploratorium and ACS on sealed-packet divers, Corning on demonstration history, and NASA on constant-temperature gases. No instructions, photographs or institutional figures are reproduced.

  1. 01
    Condiment Diver Exploratorium · Teacher Institute Science Snacks · Checked 2026-10-23
  2. 02
    Cartesian Diver American Chemical Society · Chemistry Outreach Activities · Checked 2026-10-23
  3. 03
    Making Cartesian Divers: Then and Now Corning Museum of Glass · Rakow Research Library · Checked 2026-10-23
  4. 04
    Boyle’s Law NASA · Glenn Research Center · Checked 2026-10-23
  5. 05
    Cartesian Diver · Early Apparatus Kenyon College · Historical Physics Apparatus · Checked 2026-10-23

The diver, vessel, volume bars and directional arrows are original explanatory geometry. They are distinct from water-admitting glass apparatus. Pressures 100/125 kPa, air volumes 5/4 cm³, solid displacement 1 cm³ and masses 5.5/6.5 g are invented examples. Temperature and gas amount stay fixed. We omit air mass, membrane elasticity and volume, trajectories, changing depth and drag. Pressures are absolute; differences labelled g are masses, not forces.