DIY: Cartesian Diver | Tinkerer Box Blog

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Cartesian Diver

Stem Activities

Ages: 6-8

Less than 30 minutes

Grownup needed

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Fish can freely rise or dive in water. Do you know how they do it? With just a few common materials found at home, you can discover the answer. Through this classic science experiment, you will explore the density of materials and uncover the mystery of why fish float and sink.

Materials Needed

A bottle of water
16 paperclips
Scissors
5 straws

A flat lay arrangement of craft supplies on a light wood-grain table. A clear plastic water bottle lies on its side on the left. A small pile of colorful paper clips sits in the center. A pair of black scissors is positioned to the right of the paper clips. A package of colorful plastic straws, still in its plastic wrap, is on the far right. These items suggest preparation for a craft project involving these materials.

Step-by-step tutorial

Step 1

Prepare the Straws: Bend the straws and use scissors to cut off the bent part horizontally.

Two hands are shown on a light wood-grain background. One hand holds an orange flexible drinking straw that has been bent into a small loop at the top. The other hand holds a pair of black scissors, positioned to cut just below the looped portion of the straw. The image clearly depicts the process of cutting a drinking straw with scissors.

Step 2

Insert Paperclips: Take a paperclip and insert the two ends into the openings of the straw.

Two hands manipulate a small orange section of a flexible drinking straw and a red paperclip against a light wood-grain background. The straw piece, bent into a loop, has the paperclip clipped onto it. The hands appear to be in the process of attaching or securing these two small items together. This close-up image likely demonstrates a step in a craft project.

Step 3

Attach Another Paperclip: Then, slide another paperclip onto the tail of the paperclip that is already inserted in the straw.

Two hands hold a small, looped piece of orange flexible straw with a red paperclip attached to it against a light wood-grained background. The paperclip is partially open, and the hands seem to be adjusting or demonstrating how the paperclip interacts with the straw loop. This image likely illustrates a step in a simple craft or experiment.

Step 4

Test the Setup: Now, place the assembled paperclip in water and press down on it with your hand; it will not sink.

A clear glass of water sits on a light wood-grain table against a plain white background. Two small, looped pieces of flexible drinking straw, one orange and one pink, float on the surface of the water. Each straw piece has a paperclip – one multicolored and one light blue – attached. This image likely depicts a simple science experiment demonstrating buoyancy or surface tension.

Step 5

Observe the Effects: Place the paperclip into the water-filled bottle, ensuring not to overfill it. Leave a little air at the top. If you squeeze the middle of the bottle, the paperclip will sink. Why is that?

Two hands hold a clear plastic water bottle, partially filled with water, against a light wood-grain table and a plain white background. Inside the bottle, several small, looped pieces of colorful flexible straws are connected with paperclips, forming a chain-like structure that floats vertically in the water. The hands gently grip the bottle, likely as part of a science experiment or demonstration, possibly illustrating buoyancy or the Cartesian diver principle.

The Science Behind It:

When the straw is placed in water, it floats on the surface because it contains some air. When the bottle is squeezed, the change in air pressure inside the bottle compresses the air in the straw, causing the paperclip to drop. When the air pressure returns to normal, the paperclip rises again. This is very similar to how fish regulate their buoyancy with their swim bladders. Fish control their density by adjusting the amount of gas inside the swim bladder, which affects whether they float or sink.

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