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Homework Help: Temperature and Pressure

  1. Mar 12, 2006 #1

    Fill the sauce pan with tap water. Set it close to the stove.

    Place about 2 tablespoons of water into the empty can.

    Heat the can on the stove until the water inside boils. This will not take long. You will see water vapor coming out of the top of the can when it is boiling.

    Now get ready for a surprise!

    Pick up the can with the tongs, immediately turn it upside down, then place the can in the water and pan.


    4. What gas law would account for what happened?

    5. Explain how your choice of this gas law is supported by your observations.

    I have to answer five questions-- these are the final two. I'm pretty sure I could do the last one if I could figure out the answer to the other one.

    Here are the others...may as well see if they're right and prove that I actually did the experiment and attempted the questions.:tongue: :rofl:

    1. What happened when you put the can in the water?

    When I put the can in the water, it collapsed in upon itself.

    2. Why did this happen? Make sure you relate why this happened to the changes in pressure inside and outside the can.

    "Air pressure can tell us about what kind of weather to expect as well. If a high pressure system is on its way, often you can expect cooler temperatures and clear skies. If a low pressure system is coming, then look for warmer weather, storms and rain."

    I believe the can did what it did because the air inside of it was hot until I put it in the cooler water. The cool water caused the air inside the can to cool and cooler temperatures are a signature of high pressure. High pressure means that the air is compressed into a smaller space. When the air compressed, it sucked the can in with it.

    [I'm somehow feeling that there is more to it than that or that I got this wrong because the question mentioned the pressure outside the can as well. Not sure what's really going on outside the can though... If I am missing something, is the water outside the can pressing in on it as the air inside is pulling it in upon itself?]

    3. Why did you have to turn the can upside down? (Try the experiment again without turning the can over when you put it in the water.)

    I had to turn the can upside down because when the can is put in without being turned over, it floats and nothing happens.

    Concerning four though-- would the answer be...eh, I can't decide, never mind.:rofl: My notes are confusing me (Not because I took poor notes but because I can't really understand the difference between the two laws I have written down.:biggrin: )...

    Boyle's Law- For a given amount of a gas at a constant temperature, the volume is inversely proportional to the temperature.

    Charles' Law- For a given amount of a gas at a constant pressure, the volume is directly proportional to the temperature.
  2. jcsd
  3. Mar 12, 2006 #2


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    (3) The decrease in pressure would be negated as air would rush into the can!!

    (4) Well in your investigation what are you keeping constant?
  4. Mar 12, 2006 #3
    3. Before actually attempting to do the experiment over again without flipping the can, I thought it'd be because the air inside the can could escape. The only reason I changed my answer was because I then tried it and saw that I couldn't get the can to go under the water which pretty much killed the whole thing.:rofl:

    4. The pressure? What's being changed is the temperature which causes the pressure to change-- is that right? If so, Charles' Law?
  5. Mar 13, 2006 #4
    Wow, I did terribly this time and I'm not sure where I went wrong. I thought I answered the questions correctly...:frown:

    "Please review this and answer the questions as they relate to Boyle's and Charles Laws. In #2 what happens to the volume of a gas (water vapor) when it is heated? Did any of the water vapor escape? If the experiment was done correctly some did. According to Boyle's Law when the volume of a gas expands what happens to it's pressure? By turning the can upside down you trapped a lower volume of gas (because some escaped)and a reduced air pressure compared with what is on the outside (normal atmospheric pressure). So which law more fully explained what happened?"

    Huh? I could have sworn that I did number two correctly at least...:confused:
  6. Mar 16, 2006 #5
    Okay, no replies...:frown: :rofl:

    Number one appears to be correct since he didn't comment on it.

    Number two, though...I could have sworn I addressed the question properly.:redface: When a gas is heated up, its volume increases and its pressure decreases. When I heated the water inside the can up, some of the air escaped out of the top of the can as steam. When I flipped it, I trapped what was left of the air inside the can. Since the air that was outside the can was cooler, it had a higher pressure and a lower volume. Since its pressure was greater, it was able to push in on the can. Is that right? Think it'll suffice if it is right?:smile:

    What about the other questions? Number four is still a bit confusing because I don't know what I'm keeping constant. I heated up the water which caused the temperature of the air inside the can to rise. When the temperature increased, the volume of the air changed...but didn't the pressure change as well? I'm so confused...:frown:
  7. Mar 20, 2006 #6
    :uhh: This is a relatively easy question for the pros...marking period ends this Friday...kinda in a jam...:uhh:

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