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Would a Gas Tank Float?

  1. Sep 9, 2004 #1
    Hi Guys! First Post! I really like the Forums, although most of the topics are way over my head. I'm hoping you can help me solve a problem.

    If a Truck-Trailed Gas Tanker, the kind that refuel Gas Stations, was full, would it float? Assuming there isn't any air for boyancy. My pal thinks that since gasoline is lighter than water, it would.
    On the other hand, thinking about a full sea-going oil tanker very low in the water, I think it would sink. Am I wrong? If not, how do I explain it? I tried explaining surface tension to him, but I ran out of vocabulary.

    If I am wrong, I desperately need it explained. My pal said it was "Basic" physics and it bugs the bejesus out of me, not to understand.

    Thanks for any help you could give me!

  2. jcsd
  3. Sep 9, 2004 #2

    Unless the walls of the container are really really thick compared to the enclosed volume, it must float. The only thing to worry about is the ratio of total mass over total volume. If this ratio is less than that for water, it will float.

    If you shove a conceptual oil tanker on the ocean floor, it will pop up as fast as a cork (Well not EXACTLY, I don't actually know the numbers.).

    For a true oil tanker, water pressure could deform it, causing fissures where there are weaknesses, allowing water to penetrate the oil tanks, and vice-versa, sinking it.
  4. Sep 9, 2004 #3

    Thanks for the quick response. I was just plain wrong. At least I now know why!
    Mass comparison made it very clear.

    Thanks Again!

  5. Sep 9, 2004 #4


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    Not so fast here! Just what is the density of the empty trailer?

    let mf = mass of fuel
    mt= mass of the trailer
    Vt = Volume of the trailer.

    If we have:

    [tex] \frac {m_f + m_t} {V_t} > 1 [/tex]

    The trailer sinks. we must know the volume and mass mass of the empty trailer before any conclusions can be made. Note that the mass and volume must include the ENTIRE trailer not just the tank. Some trailers may sink other may float it is entirely dependent on the construction of the trailer, that has not been specified so there is no possible answer.
  6. Sep 9, 2004 #5
    Integral, thanks for the response as well. I think Gonzolo(Sorry for the bad spelling, earlier!) gave me the ballpark answer I was looking for.

    Now that I think I understand it, for my question I could have asked if a balloon the size of a tanker, full of gas would float. My pal and I couldn't get deep enough for the mass of the trailer. Way, way out of our league! But I really do appreciate the idea. I think when I bring it up to him, I'll say the trailer was built like a tank and I was taking that into account. :) Might get out of buying him a beer!

    Thanks Guys!

  7. Sep 10, 2004 #6


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    As far as the point about the full tanker ship riding low in the water: An empty tanker is "full of air" and while the density of oil is less than that of water, it is still greater than the density of air! Replacing air with the heavier oil is what causes it the ship to ride lower in the water.
  8. Sep 10, 2004 #7


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    And, in fact, tanker ships that are empty bob like a cork - if they are going to be steaming for any amount of time empty of oil, they take on water for ballast.
  9. Sep 10, 2004 #8


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    The first really deep submersible, the Trieste, was essentially a big floating gas tank. The main body of the submersible looked very much like the tank you would see being pulled by a semi truck, and was full of kerosene (if I remember correctly, but it was some kind of petroleum product at any rate). The reason they chose a petroleum product rather then air is because the oil would not be crushed by the great depth. The submersible went straight down to the bottom of the Mariana's Trench at a place called the Challenger Deep, the deepest spot in the oceans. After sitting for a while, they released the weights, and the big metal can filled with gas floated back to the surface.
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