Density Divers Experiments

Experiment Procedure

1. Fill the plastic soda bottle almost to the VERY top rim with water.
2. Fill the glass eyedropper with just enough water so that it barely floats in the deep container. You‘ll have to adjust the amount of water needed in the eyedropper to make it float. If the eyedropper sinks, just squeeze some water out of it a few drops at a time. It won’t take much.
3. Place the eyedropper into the soda bottle. The eyedropper should barely float and the water in the bottle should be overflowing the bottle. Be sure to add more water if needed! Seal the bottle with the cap.
4. Squeeze the sides of the bottle and notice how the eyedropper (now called a diver) sinks. Release your squeeze and it floats to the top. Make water level adjustments in the diver as needed so it moves easily without you having to break your fingers on the squeeze.

Experiment Procedure

1. Slip a large hex nut onto the stem of the pipette and slide it upward until it stops. Give the hex nut a nudge as you screw it onto the base of the pipette. A few turns holds it in place. Leave about a 1/4-inch (6 mm) gap between the hex nut and the bottom of the bulb of the pipette.
2. Use scissors to cut off the stem of the pipette about 1/4-inch (6 mm) below the hex nut.
3. Use the deep container to test-float the diver in the water. The diver will bob up and down and the bulb will stick out of the water. Squeeze and release the bulb a little to draw some water into it. The correct adjustment means the diver should just barely float in the water. If it sinks, grab it, squeeze out a few drops of water, and re-test it until it floats properly.
4. Fill a soda bottle all the way to the brim with water. Carefully place the diver into the soda bottle without losing any of the water from inside the diver. If you do, you’ll have to test-float the diver again! Put the cap tightly on the totally full soda bottle with the diver inside.
5. Squeeze the sides of the bottle. You should be able to squeeze the bottle almost invisibly and the diver quickly sinks and stays on the bottom until you release the squeeze. Depending on the amount of water in the diver, you may have to squeeze very hard (with both hands, even). Adjustments in the amount of water in the diver may be needed. Take your time. Even the experts have to do this step!

This version of the Cartesian Diver that uses the plastic pipette and hex nut was created by Bob Becker from Kirkwood, Missouri. The SQUIDY character was the creation of Steve Spangler in 1991.

Experiment Procedure

1. Build another classic Cartesian diver using a pipette and a large hex nut as you did before.
2. Being careful not to tear the rubbery material, slide SQUIDY snugly over the bulb-end of the diver so the bulb is covered completely and seems to disappear. There can’t be bubbles trapped between the diver and SQUIDY. Check the rounded end and push out any air.
3. Now that you’ve added a little more weight, adjust SQUIDY’S ability to float. Use the deep container to test-float SQUIDY in the water. SQUIDY will bob up and down and will stick out of the water. Squeeze and release SQUIDY to draw some water into it. The correct adjustment means it (she? he?) should just barely float in the water. If it sinks, grab it, squeeze out a few drops of water, and re-test it until it floats properly.
4. Place SQUIDY into the soda bottle by gently twisting it back and forth so the legs get into the bottle undamaged. Make sure that the bottle is completely full! Screw the lid on tightly and give the bottle a squeeze. You should be able to squeeze the bottle gently, almost invisibly, and SQUIDY quickly sinks and stays on the bottom until you release the squeeze. Make whatever water level adjustments are needed in the diver to get the movement you want.

Experiment Procedure

1. Build two pipette Cartesian divers as you did before but use two small hex nuts this time. Be sure to leave at least a 1/4-inch (6 mm) gap between the hex nut and the bottom of the bulb of the pipette on each one.
2. Wrap the blue wire three times around one diver in the gap between the hex nut and the bulb. Shape the other end into a long hook hanging straight below the diver. Wrap the red wire around the gap in the other diver in the same way but form it into a big loop over the top of the diver. Wrap the loose red end around the gap on top of the first wrap.
3. Add water to both divers. The hooking diver (blue wire) needs to float and sink on “command” so adjust it to do just that but use as little water as you can. It needs to be able to lift the other diver to the surface. The target diver (red wire) needs to just barely sink so it can be hooked and lifted off of the bottom.
4. Carefully place the target diver into the bottle first and let it sink. Add the hooking diver next and fill the bottle to the top like before. Tighten the cap to seal it. Squeeze the bottle and attempt to hook the target and pick it up from the bottom. It’s tricky so plan on some practice but it’s also great fun!

Experiment Procedure

1. Build five pipette Cartesian divers as you did before using a small hex nut on each one.
2. Use the marker to number the bulbs of your divers one through five.
3. Fill all of your divers with water in the deep container. It’s important that they start out filled to the same level so that they all barely float.
4. Place the diver labeled “1” into the soda bottle filled with water. Be extra careful not to lose any of the water from the diver.
5. Pick up diver #2 and squeeze three to five drops from it. Count carefully. Make sure not to squeeze out any more! Then place it into the bottle with diver #1.
6. Pick up diver #3 and squeeze six to ten drops from it. Carefully place it into the bottle.
7. Repeat the process for the remaining divers. Squeeze nine to fifteen drops from number four and twelve to twenty drops from number five. When all the divers are in the bottle, fill it to the brim with water and tighten the cap to seal it.
8. Squeeze the sides of the bottle. As you do, the divers should drop to the bottom in order one through five. You may need to use both hands to get the last couple of divers to drop. Release your squeeze and the divers should rise to the top in reverse order!