Instructions for:
Bottle Divers
The Bottle Diver is an effective demonstration of the concepts of pressure, volume, weight, and the properties of liquids and gases.
The Bottle Divers arrive as two clear plastic bottles with caps, each containing three small glass vials with lids. Notice the small holes in each lid. To prepare the demonstration, remove the vials, and check that the lids are on tightly. Fill the plastic bottles with water, almost to capacity, until there is only enough airspace left to accommodate the vials later without overflowing. Pop the vials in, with the lids facing downwards, and screw the caps on the bottles.
To activate, squeeze the bottle slowly. As pressure is applied, you will notice that the water level in each small vial increases. As the system is further pressurized, the vials eventually sink to the bottom of the bottle.
With use, the vials will fill up with water (especially if the bottle is shaken or handled roughly) and cease to float. To fix this, hold the bottle upside down over a sink or container (waiting for the diver to sink into the neck of the bottle) and unscrew the lid. Because the vial is blocking the neck, you won't get as wet as you would expect. A slight squeeze and the vial pops out. Empty the vial, refill the bottle, and close up the bottle again.
The bottle cap may leak a little, or some curious student may loosen it. It is a useful precaution to have some towels on hand, as well as placing this station away from things that shouldn't get wet.
Questions for Students / Items of Interest:
Q1) Why does the Bottle Diver dive?
-When you squeeze sides of the bottle, you increase the pressure inside the bottle. The water and the air trapped in the vials are pressurized identically. However the air will compress far more than the water. This allows water to enter the vial, which makes it heavier: it contains the same amount of air as before, but also an added amount of water. When the weight of the vial increases sufficiently, it will sink. When the pressure is released, the air expands, pushing the water out, and making the vial lighter, causing it to float. The cycle can be repeated any number of times.
Q2) Can you make the divers suspend in one place in the bottle?
What is happening at this point?
Q3) If you pour out half of the water in the bottle, it becomes much harder to sink the diver. Why?
- The bottle is much squashier, and deforms so that it is touching your hand over a larger area. To achieve the necessary pressure, you must exert a larger force.
Copyright 2004 Straley/Pinney - The University of Kentucky Physics Petting Zoo