Cartesian diver

How to make a cool physics toy at home

Safe­ty pre­cau­tions

This is a safe ex­per­i­ment. MEL Sci­ence rec­om­mends per­form­ing it with your chil­dren!


  • a plas­tic wa­ter bot­tle;
  • a wood­en “div­er” (you can also use match heads);
  • a glass of wa­ter.

Step-by-step in­struc­tions

Put a wood­en “div­er” in a wa­ter bot­tle, fill to the brim with wa­ter, and close tight­ly. We strong­ly rec­om­mend us­ing a screw cap bot­tle. Wait 15 min­utes for the “div­er” to be soaked through. Then squeeze the bot­tle and watch it em­bark on its dive.

You can demon­strate how wa­ter fills the pores us­ing an in­vert­ed glass jar half-filled with wa­ter.

Process de­scrip­tion

The div­er is made of wood, which has a por­ous struc­ture. These pores are filled with air. When the bot­tle is squeezed, the pres­sure in­side of it in­creas­es. As the wood pores are com­pressed, the air is forced out of them and they are filled with wa­ter. The “div­er’s” av­er­age den­si­ty in­creas­es and it be­gins its jour­ney down­ward!