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The Cartesian Diver Experiment

  1. Mar 9, 2006 #1
    Has anyone ever done an experiment called "The Cartesian Diver"? The instructions are below, just in case...:smile:

    1. The medicine dropper is the "diver" which will be put into the water.

    2. Fill the graduated cylinder with water to about an inch from the top.

    3. Fill the medicine dropper almost the entire way with water. You may need to turn it over and fill it to get enough water into the dropper.

    4. Place the diver into the graduated cylinder. It should just float on top of the water. If it sinks, you have too much water in the dropper. Take it out an release one or two drops of water.

    5. Cut the balloon in half following the diagram.

    6. Stretch the balloon to cover the mouth of the cylinder tightly and wrap the rubber band around the top to hold the balloon tightly in place.

    7. Press on the balloon with your thumb. Watch the diver closely. Look at the water level in the diver. The diver should sink to the bottom of the cylinder. IF IT DOES NOT SINK, there is not enough water in the diver. Repeat steps 2-6, putting more water into the dropper.


    I've done the experiment so now I have to do the questions.

    1. What happens to the air in the top of the graduated cylinder when you press on the balloon?

    When I press down on the top of the graduated cylinder, the air is pressed down as well.

    2. What does this do to the water level in the diver? Why?

    The water in the diver seems to go up to the top of the medicine dropper.

    3. What happens to the air in the diver when you press on the balloon?

    When I press on the balloon, the air in the diver appears to be going towards the bottom of the medicine dropper.

    4. Why does the diver sink?

    The diver sinks because the volume of the air decreases.

    5. This is a demonstration of "Boyle's Law" which relates pressure and volume. Fill in the blanks below:

    When air pressure increases, the volume of the air _______________. [decreases]

    When air pressure decreases, the volume of the air ______________. [increases]


    Could someone tell me if what I have now is right? I don't know the "why" part for number two and I don't think I have number four right (and/or explained all that well). If someone could explain it to me or give me a link, I would appreciate it.:smile:
     
  2. jcsd
  3. Mar 10, 2006 #2
    ohh man i wrote a huge explanation but after reaing it i became really confused.
    1-When water goes inside (because the air was compressed, the divers weighs more, making the density greater.
    or
    2-When air is compressed the volume of the diver changes and is decreased, making densty greater.
    or
    3-Both...

    I wrote a big explanation on the 2nd one, but then i thought about it, and the i came with the 1st idea i stated above...which makes more sense to me. In other words, i beleive the volume is always the same, unless volume = the total space with no particles in it inside an object which would mean both 1st and 2nd idea are true...

    Sry i couldnt help you that much except give you some ideas.

    though i could help you by giving you this link:
    http://physics.about.com/cs/airandfluidexp/a/040703a_2.htm
    But makes me unsure of which of my ideas is right.
     
  4. Mar 11, 2006 #3

    Ouabache

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    Science Advisor
    Homework Helper

    1. What happens to the air in the top of the graduated cylinder when you press on the balloon?
    When I press down on the top of the graduated cylinder, the air is pressed down as well.
    yes, but what happens to the pressure of that air?

    2. What does this do to the water level in the diver? Why?
    The water in the diver seems to go up to the top of the medicine dropper.
    first part is correct. The why part has to do with what is happening to the pressure in the water
    3. What happens to the air in the diver when you press on the balloon?
    When I press on the balloon, the air in the diver appears to be going towards the bottom of the medicine dropper.
    it may appear so, but does the size of the air bubble stay the same?
    4. Why does the diver sink?
    The diver sinks because the volume of the air decreases.
    that's only a partial answer, why would the diver sink when the volume of air decreases? [hint: has to do with buoyancy]
    5. This is a demonstration of "Boyle's Law" which relates pressure and volume. Fill in the blanks below:
    When air pressure increases, the volume of the air _______________. [decreases]
    correct
    When air pressure decreases, the volume of the air ______________. [increases]
    correct

    btw, this same process occurs if you were a scuba diver and submerged to various depths of water. The air bubble would be the volume of air in your lungs and the pressure changes relative to depth. If you were neutrally buoyant at some depth, you would neither sink nor float. However if you inhaled you increase the air space in your lungs and you float up, if you exhale, you decrease that same air space and sink. That is an important way divers can control their vertical position while submerged.
     
    Last edited: Mar 11, 2006
  5. Mar 12, 2006 #4
    Thank you, I appreciate the help. ^_^
     
  6. May 13, 2008 #5
    for question # 1.
    what happens the the air pressure?
     
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