The Omnifarium - Science/BottleDiver.html

The Bottle Diver

Category: Science
Wed, 03 Oct 2007, 12:00

Here's a fun and easy science demonstration you can use to amuse your kids that needs just a two liter plastic pop bottle and a medicine dropper.

First, fill a tall glass with water and drop the empty medicine dropper into it. The eye dropper should float in the water. Next, completely fill the medicine dropper with water. It should now sink in the water. Now, carefully squeeze water out of the dropper until it just floats in the water. Then, squeeze out a couple more drops out of the dropper.

Now, fill the two liter pop bottle with water right up to the top and put the medicine dropper into it. A bit of water should spill out the top of the bottle. Put the cap back on the bottle and tighten it closed. You're now ready for the demonstration.

At first, the medicine dropper should float at the top of the bottle. But when you squeeze the bottle, the medicine dropper should sink. With the right amount of force, you can adjust the depth of the "diver" within the bottle.

Before reading on, try to reason out why this works.

Ready for the answer? When adjusting the amount of water in the medicine dropper, think about when it sank or floated. With a lot of water, the dropper sank, but with little water, it floated. To put it differently, with little air in the bulb, it sank. Containing a lot of air, it was buoyant and floated.

What happens when you squeeze the bottle? Do you compress the water? Or do you compress the air in the medicine dropper? With a smaller volume of air in the dropper, it becomes less buoyant and sinks.

With this story, I open a new section of my blog devoted to science.

Hans

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