Ocean AdVENTure! - InterActivity #3: Pressure

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Atmospheric Pressure

Activity One: Determine the Pressure on Our Submersible

Background:
At sea level, the atmospheric pressure of the air on us is 14.7 pounds per square inch. Descending into the sea, atmospheric pressure increases by one atmosphere for every 33 feet (10 meters).

Problem:
If we are in the submersible at 2222 meters (7290 feet), what is pressure per square inch on our ship?

Answer:
220.9 atmospheres, or 3247.23 pounds (1.6 tons) per square inch; 1,473 kg or 1.4 metric tons.

Solution:
7290 feet divided by 33 feet per atmosphere= 220.9 atmospheres

220.9 x 14.7 = 3247.23 pounds

3247.23 divided by 2000 pounds in a ton= 1.6 tons

Activity Two: An Easy Experiment to Try

This simple experiment can help you understand the principle of the Alvin's descent and ascent.

Background:
Remember that the Alvin pilot has steel weights, usually four at 250 pounds each, and water as ballast. Both help the submersible descend. When the ship nears the desired depth, the pilot throws off two of the weights so the ship achieves neutral buoyancy, or floats. To make the submersible ascend to the surface, the pilot makes the ship lighter by throwing off the remaining weights and releasing the water in the ballast tanks.

Required Materials:

a soft- plastic bottle with top (a 2-liter soda bottle or milk jug is good)
an eyedropper
water

Method:

Fill the bottle nearly to the top with water.

Insert the eyedropper in the water, squeezing the bulb until the eyedropper floats in the water with its bulb just above the water.

Cap the bottle tightly.

Now, to simulate the increasing pressure of descent, press with your hands on the sides of the bottle and keep pressing while you or a partner observe what happens.

You should notice that the eyedropper goes down deeper in the water. This descent is caused by increased pressure forcing more water, and hence more weight, into the dropper.

Decrease pressure by slowly removing your hands from the sides of the bottle. The eyedropper should float upward. This is due to decreased pressure forcing water out of the eyedropper, which makes it lighter, in a manner similar to the submersible pilot's letting air out of the ballast tanks and dropping the second set of weights.

Fahrenheit? Celsius? No problem! -->
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