Cartesian Diver Toys – Hook the Sinker

Let your mind latch onto science and fun with this fun game that teaches properties of air, density and water.

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Hook is an amazing game that combines cool science with coordination and skill. You’ll make a special diver, float it in a soda bottle tank and then use your talent to retrieve sunken treasure! Hook is an updated version of a classic science experiment called a Cartesian Diver. Get ready to challenge your friends to a game of Hook! Discover the relationship between air pressure and density, and how to make a floating diver more or less buoyant. Float or sink? It’s your choice!

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Here's What You'll Need

  • Water
  • 16 oz. cup
  • Scissors
  • 2 hex nuts
  • 2 pipettes
  • 1-liter bottle with cap
  • 10" piece of wire
  • 6" piece of wire


  1. Slip the hex nut onto the stem of the pipette and slide it upward until it stops. Screw it onto the base of the bulb. A few turns will hold it in place. Cut the stem a quarter-inch above the base.
  2. Pour about 4 inches of water into the large plastic cup. Test-float the diver in the cup. It should bob up and down with the bulb sticking out of the water. Squeeze the bulb and draw some water into it by releasing your grip. Repeat this several times until the diver is half-full with water.
  3. Let go of the diver to see if it still floats. When properly adjusted, the diver should just barely float in the cup of water. If the diver sinks to the bottom, grab it, squeeze out a few drops of water, then re-test it until it floats properly.
  4. Fill the soda bottle all the way to the brim with water. This is VERY IMPORTANT! Place the diver in the bottle, but be careful not to lose any of the water inside the diver or out of the top of the bottle. If you do, you’ll have to test-float the diver again!
  5. Put the cap on the very full soda bottle with the diver inside! Squeeze the sides of the bottle. Does the diver sink? You may have to squeeze very hard with both hands, depending on the water level in the diver. What happens when you release the squeeze?

Make another Cartesian Diver, with the directions in the first activity. (You need two divers to play Hook.)

  1. Wrap one end of the blue wire several times around the stem stump of the Cartesian Diver you’ve already tested. Make sure you wrap the wire between the bulb and hex nut. Shape the other end of the blue wire into a giant, J-shaped Hook.
  2. Wrap one end of the red wire around the stem stump of the second diver between the bulb and the hex nut. Loop it over the diver’s bulb and wrap the other end around the stem stump, too. This diver will act as the Sinker.
  3. Set up a float test for the sinker in the large plastic cup, just as you did when you built the first Cartesian Diver. This time, however, fill the sinker with enough water so it barely sinks to the bottom of the cup.
  4. Top off the soda bottle with water, pull the sinker out of the test cup and drop it into the top of the bulging soda bottle. Again, make sure that the bottle is absolutely full with water (the diver won’t work if there’s any air in the bottle). Check the bulb to make sure that it hasn’t lost any water and then drop the diver with the hook into the bottle. Screw the cap on the bottle as tightly as you can.
  5. Squeeze the sides of the bottle. The hook will dive to the bottom. The object of the game is to catch the sinker with the hook and lift it to the surface. You may have to make some adjustments on both the hook and sinker to get this to work, but it’s all part of the game!

How Does It Work?

The Cartesian Diver is a classic science experiment that’s hundreds of years old. It’s named for a Frenchman, René Descartes (1596-1650), who made huge contributions in the fields of philosophy, math, and science. The original Cartesian Divers were made out of glass medicine droppers or delicate glass ampules.

When you have the water levels adjusted correctly in your new, unbreakable divers, you should see the water in the diver rise as you squeeze the bottle. The air trapped in the pipette compresses into a smaller space and the diver’s weight increases. It becomes less buoyant and it sinks. When you release the squeeze, the compressed air expands and forces water out of the diver, allowing it to float to the top of the bottle.

Note: If the bottle requires a super-strong squeeze to move the diver, there isn’t enough water in the pipette. Remove the diver from the bottle and increase the water level in the diver so it just barely floats.

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