Simple Science: Cartesian Diver, learning about buoyancy

Do this fun experiment/ game to learn about buoyancy and air pressure.

 Cartesian Diver game with water bottle for kids Supplies:

2 hex nuts
2 pipettes
2 wires (we used red and blue)
1 500ml plastic bottle with lid
water

 

  1. Snip the pipettes about 2/3 of the way up.  You will be using the bulb part.
  2. Slip the hex nut onto the pipette bulb and screw it onto the base of the bulb to secure it
  3. Wrap one end of blue wire around stem stump of pipette, curving the other end to make a hook
  4. Wrap the red wire around end of second pipette, starting at the stem, looping it around top of pipette bulb, and securing back at the stem

make a cartesian diver

5. Fill each pipette about 1/2 full with water by squeezing bulb, putting into water, and releasing bulb.

6. Test the buoyancy of each pipette bulb – fill the red one with enough water to make it sink in a cup of water.  It will probably be just over half full with water.  Fill the blue pipette so that it floats in a cup of water, just below the surface.  Ajust water levels in each pipette to get correct buoyancy.

testing cartesian diver experiment for kids testing cartesian diver experiment for kids

 

To play the game:

Fill a 500 ml bottle with water.  Drop the red pipette into the bottle.  It should sink to the bottom.  Drop the blue pipette into the bottle.  It should float almost at the surface.  Make sure the bottle is completely full with water, and secure lid.  Gently squeeze bottle.  When you squeeze the bottle, the floating pipette should dive down.  Try to hook the pipette that is sunk, and bring it to the surface!

make a game to play using science

How it works:

Buoyancy: when your pipette is less dense than the water it is in, the pipette will float.  When the pipette is more dense than the water it’s in, it will sink.  The combination of nut + water + air in the pipette will be just heavy enough to sink if you add more water, and float if you add less.

Pressure: When you squeeze the bottle, you are increasing the pressure, making the air trapped in your pipette compress, which means more water can creep into the pipette.  This makes it makes less buoyant causing it to sink.   When you release your squeeze, the air expands, pushing water out of the pipette, making it more buoyant so it floats.