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Strong force question

  1. Mar 26, 2015 #1
    I wasn't sure where to post this, but about a week ago, I sat a test called GAMSAT which has a science section comprising 20% physics, 40% chemistry and 40% biology. Physics isn't exactly my strong point, however, the developers cite needing only high school level understanding (I stopped physics in year 10). In one of the physics questions, it talked about the strong force, and displayed a graph of energy (y axis) vs distance (x axis).

    I might be totally wrong, but I went on the assumption that strong force energy increased with distance, as I had an interest in strong force theory a while back when i still did physics in high school. However, the graph showed an exponential decrease with energy, and this conflicted with what i knew (or thought i knew xD) about the strong force. The question asked whether the energy increased, decreased or remained constant. I chose increased, but going by the graph alone, the answer would be decreased. Am I thinking of all this wrong? I asked a friend who is very good at physics, and he told me that energy goes down, momentum goes down, but strong force goes up. Can anyone shed light on what happens?
  2. jcsd
  3. Mar 26, 2015 #2


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    It is difficult to answer this because you did not include the graph. All we have to go by is your description of it. What if you misread or misunderstood the graph? There's no way for us to find out because we can only go by with what you wrote and not see the actual graph. I know this is from a test, but you also need to be reasonable in asking for answers when it is like this.

    See this thread, for example, on how it should be done:


    It is why we always tell people to cite the source. We can't tell if you read it incorrectly, misinterpret it, or simply didn't understand it. Without the source, there is no way to tell!

  4. Mar 26, 2015 #3
    I definitely didn't misread the graph as I asked my friends this same question, and they all confirmed they went by the graph showing a decrease. I can show how I remember it looking like, but the units are in joules for energy and femtometres for distance:
    https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/64/64072-798e05f54b5e81b2b7267350248718df.jpg [Broken]
    It's not the exact graph, but the curve is essentially the same.

    Attached Files:

    Last edited by a moderator: May 7, 2017
  5. Mar 26, 2015 #4


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    Don't you also have the entire question? I think it is clear in my post that we require the whole thing, in full, not just in bits and pieces.

  6. Mar 26, 2015 #5
    The question did have a passage of background information explaining what the strong force was, but the question itself (along with most other questions) are simply one liners With more than 100 questions in the test, and stress levels high, I don't remember the question word to word, but it asked whether the energy associated distance A. increased, B. decreased, and C. remained constant.
    Last edited: Mar 26, 2015
  7. Mar 26, 2015 #6


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    Well, for the graph you drew, that's an easy question - it decreases with distance over the range illustrated in the graph.

    If you want to ask whether the graph you drew accurately reflects the behavior of the strong force at distances below one femtometer in a particular nucleus (one femtometer is less than the size of most nuclei, so this will affect the size more than the stability of the nucleus) that's a fair question for this forum.

    Whether these answers have anything to do with the test question is a different matter. You are the only one here who has seen the test question, so you're the only person who can judge this.
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