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How Does The Cartesian Diver Experiment Work?

The Cartesian diver, named after French philosopher and scientist René Descartes, works because of several factors.

Bottles with experiment

Photo: TeaWithBuzz (Flickr)

Here's what the experiment looks like!

Last time we explained how to make a Cartesian Diver. You fill a clear plastic bottle with water and place an eye dropper in it. The eye-dropper should have just enough water inside it so that it barely floats.

Now seal the bottle tightly and squeeze on its sides. The eye-dropper sinks! Stop squeezing and the dropper rises once more. Today we’ll explain why this works.

How Does It Work?

The Cartesian diver, named after French philosopher and scientist René Descartes, works because of several factors.

When you squeeze the sides of the bottle, you are increasing the pressure on the liquid inside. That increase in pressure is transmitted to every part of the liquid. That means you are also increasing pressure on the eye dropper itself.

Squeeze hard enough and you will push some more water up inside the dropper. The air inside the dropper squeezes tighter as more water is forced in.

Increasing The Density

Now, water is much denser than air. So when you push more water inside the dropper, you increase its overall density. Once its density is greater than that of its surroundings, it will sink.

Release the pressure on the bottle’s sides and you stop forcing water inside the eye- dropper. The air inside it will now push out the extra water again, and the eye-dropper will rise. That’s the Cartesian Diver!

  • Doug mckinney

    So, without access to clear plastic bottles, how did Mssr. Descartes perform this experiment?

  • dimitri poppeliers

    Better description than wipipedia in some respects other than the part about water being “compressed”.

  • jimmy slavill

    he probability used some non clear plastic bottles

  • Qusai


  • your mom


  • your mom

    yo yo yo

  • Jody Willis

    This is not correct. Pressure does not change the density of the water, instead it allows the air inside the dropper to contract, causing it to displace less water, and then become less buoyant.

  • rmly b yahaya

    The object sinks if the upthrust is less than its weight, but floats if the upthrust is equal to, or more than its weight.

  • fabian montano

    The object drops because the pressure that has on it makes it sink down

  • Name

    It doesn’t say that it is changing the density of the water; the pressure pushes more water into the dropper changing the density of the system that is the dropper and its contents. The buoyancy of the dropper does not change, however, as its volume does not change, so actually you’re incorrect.

  • Ioan Grosu

    Can anyone keep the eye dropper at rest at the middle of the bottle ?
    If YES let me know .

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