This Cartesian diver video can be found here: http://www.youtube.com/watch?v=GDDmU-C21EE

Have students use a Sharpie marker to draw a line where the water is located. Ask the students to observe and infer what happens to the bulb when the bottle is firmly squeezed. Later in your presentation you could have students calculate the change in the bubble's size to cause it to accelerate down at 1 m/s².

Troubleshooting

• If the bulb is difficult to sink, make sure there is no air in the top of the bottle. If there is air in the bottle, when it is squeezed, the air compresses before the water.
• If the pipet's bulb floats higher than about 2 mm above the water, it make be too buoyant and require extra force. Readjust he amount of water to increase the water in it without sinking.

This is a simple make and take. It is amazing how many people have not done this. You will be surprised how many students will "dig this" activity.