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Conversion pounds per square inch/pascals

  1. May 4, 2015 #1
    Heya guys, I am having a problem converting units like pascals and pounds per square inch. I do not understand, what "area" of measurement does a pascal cover as opposed to a "pound per square inch" obviously being in an inch, the pascal is per what area?


    For example when I try this to help me;

    Which I type into google, it cannot convert the units when I specify the area. i want to find out how much X number of pascals acting in the area of a square mm would be in pounds per square inch.
     
  2. jcsd
  3. May 4, 2015 #2

    Doc Al

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    A pascal is a unit of pressure, not force. (So pascal per unit area is not what you want.) The definition of a pascal is 1 Newton per square meter: 1 Pa = 1 N/m2.
     
  4. May 5, 2015 #3
    I am confused because I have pressure in an area, but is not possible to find force from that?

    My problem is I know that there is 11 Terapascals at work in a square millimeter area. The surface being tested for this pressure can withstand that, but I want to know how much pressure the same object can receive in a square inch and some how work out force as well. Can I do this?
     
  5. May 5, 2015 #4

    Doc Al

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    Sure you can. Given pressure and area, you can find the force. Pressure = Force/Area, so Force = Pressure*Area.

    Assuming you keep the pressure constant, the force is proportional to the area.
     
  6. May 5, 2015 #5
    I see, so 11 terapascals per square millimeter would be 11 terapascals multiplied by a square millimeter in meters? So 11 terapascals x 1 000 000 is 11000000, what is this number? newtons?


    I do not suppose you mind giving me an example using my numbers? So if I wanted to find out how much pressure an area of a square inch can take from my findings that a square mm can take 11 terapascals, would I multiply those terapascals by 645.16 to get the amount in a square inch?


    Edit;


    I did another one which may help me, can I just scale up to meters squared for ease? So scale up 11.6 terapascals per square mm, to 11.6 exapascals per square meter and go from there? so to find force, 11.6 exapascals are equel to 1000000000000000000000000 newtons?
     
    Last edited: May 5, 2015
  7. May 5, 2015 #6
    Read up on the MKS (metric) unit system and the definition of pressure.
    With 1 terapascal you risk blowing up your tyre.
     
  8. May 5, 2015 #7
    it will probably be a pretty interesting tyre if one was made that takes that sort of pressure though. Although I am not talking about pressure inside a tyre, I mean pressure made on contact with a surface.
     
  9. May 5, 2015 #8

    russ_watters

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    You are still saying and using the units wrong. There is no "11 terapascals per square millimeter". The word "per" means "divided by". You have 11 terapascals applied to an area of 1 square milimeter. And a milimeter is 1/1000 meters, not 1000 meters.

    It would help a lot if you used more mathematical rigor here: write out the numbers with the units and manipulate them together. Then you'll be able to cross-out the units that cancel and see what you are left with. For example: http://www.ifa.hawaii.edu/~barnes/ast110_99/units.html

    And for Pascals, since now you know a pascal is a newton per square meter, you can stop using the word "Pascal" when doing the math.
     
  10. May 5, 2015 #9
    So how would I explain 11 terapascals applied to 1 square mm in that format? Bear with me, since I have never explained anything in that format before, certainly not anything more complicated than basic addition anyway.


    And a square meter is made of up 1 million square mm no?
     
  11. May 5, 2015 #10

    russ_watters

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    "applied to" means you multiply. Since p=f/a, if you multiply by "a", the "a's" cancel out and you are left with "f".
    Correct. But you weren't asking about applying newtons per square milimeter to a meter, you were asking about applying newtons per square meter to a milimeter.
     
  12. May 5, 2015 #11

    Doc Al

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    Careful with how you phrase it. It's not "per" square millimeter.

    A pressure of 1 teraPa exerts a force of 1 teraNewton over an area of 1 square meter. Over a square millimeter, the force would be one millionth as much.
     
  13. May 5, 2015 #12
    So 11 Tp applied to 1 square mm= 11 Tp x 1 square mm?

    So from there, my goal is to find out how much pressure this surface can "take" in a square meter after it has displayed the ability to take 11 Tp x 1 square mm

    From there, I guess I can more easily find force which is as Doc said.


    In my example the reverse is true however? 11 teraPa is being applied/exerted to a square mm and not a meter?

    Is 11 teraPa applied to one square mm the same as 11 exapascals applied to a square meter?
     
  14. May 5, 2015 #13

    Doc Al

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    To find the force exerted on a surface, multiply pressure times area. If you use units of Pa and m2, the force will be in Newtons.

    You still seem to mix up pressure and force, so I don't really know what you are trying to do.

    Again, don't mix up force and pressure.

    Please answer this question, assuming a constant pressure: Say there is a pressure of 14 Pa exerted on one square millimeter. What would be the pressure exerted on one square meter? On one square inch? On one square mile? (Hint: If you are calculating anything, you are confused.)
     
  15. May 5, 2015 #14
    So are you telling me its just 14 Pa regardless of what is being exerted on? so 14 Pa exerted on one square mile is the same as it is exerted one square millimeter? Based on your hint thats the only way I would understand it without calculating anything....


    I want to know how much a surface can take in pressure in an area bigger than what i already have. So imagine I have a wall, and I tap it with my hand for 10 pascals of pressure in a square inch, how would I know how much the wall would take in pressure if it was a squire mile in size, and I was slapping it with a square mile hand.....as a crazy example.

    Or if I was stabbing the wall with a pin, excerted 10 pascals of pressure in a square mm, then slapped it with my hand, how would I find out how hard I would have to slap to indent the surface the same as I did with the pin, only with my hand?
     
  16. May 5, 2015 #15

    Doc Al

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    That is exactly right. The force changes with area, not the pressure. (Assuming you keep the pressure constant.)

    Compare it to density (mass/volume). If I measure the density of 1 gram of gold or 1 kg of gold, would I get a different answer?
     
  17. May 5, 2015 #16
    Ok I think I get it. So if something can take a lot of pressure exerted on it without deforming in a small surface area, it would take a large amount more force to reach the same pressure on a large surface area.

    So back to my example, my surface has survived without deforming or indentation 11.6 teraPa in a square millimeter. So ti find force required to reach that in a square meter I take that pressure and multiply it by area, which is just 1 meter, so 11.6 teraPa x 1 = 11600000000000 newtons?
     
  18. May 5, 2015 #17

    Doc Al

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    Yes. To create a pressure of 11.6 teraPa on a square meter would require a force of 11.6 teraN.
     
  19. May 5, 2015 #18
    You seem to be not at ease with the elementary notion of "pressure".
    This is one of the first if not the first concepts that is taught in a high school physics class.
    Yet you appear to be discussing what appears to be some kind of pressure anvil.
    A pressure of 11 TP applied to 1 mm2 requires a force of 11 MN, that is a weight of about a million kilograms.
    That is physics laboratory stuff.
    I am puzzled.
     
  20. May 5, 2015 #19

    Doc Al

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    Me too. These numbers seem highly unrealistic.
     
  21. May 5, 2015 #20
    Is 11 TPa enough to make a black hole ?
    Just to spice up the discussion and attract the usual cranks ;-)
     
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