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The need of definitions in physics

  1. Jul 7, 2013 #1
    My high school physics textbook gives much emphasis on memorizing definitions.We have to memorize the definition of force, inertia, etc...We have to write the definitions as it is in the textbooks...
    For example, the definition of "force" in physics textbook is,
    "Force is defined as that which when acting on a body changes or
    tends to change the state of rest or of uniform motion of the body along
    a straight line."
    The comical part is that we don't apply force to solve mechanical problems but we memorize it's definition..
    "Mark", here measures academic achievement. The marks for the above definition is 3 marks.
    I had difficulty memorizing tough definitions like these and I got low marks(Also due to weak memory). I always criticized the edu system for making the students rote learn the concepts. For 10 marks, we have to memorize the derivations. When we write some other derivation, the teacher strikes it off.
    There is very less of problem(Plug and chug type) solving involved in my textbook which too I didn't like. The same problems are asked for the exams without even changing the numbers!
    You may take a look at my school textbook;


    Now, I will come to my point. For mathematics, many definitions are used exactly. For example, epsilon-delta definition of limit is used in solving problems pertaining to limits. So, memorizing the definitions is of much help in mathematics for solving problems, I suppose.

    Will memorizing the definitions do much help in physics, if not in classical physics, atleast in higher physics like relativity and quantum mechanics?

    In many posts in physics forums, I have seen that members insist in following the definitions for many terms in higher physics.

    So, please help the role of definitions in physics
  2. jcsd
  3. Jul 8, 2013 #2

    Simon Bridge

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    Definitions are very important when you do physics.
    A lot of the confusions in these forums come from not being careful about the definitions.
    What your course is doing is getting you into the habit of being precise in your language - if you define all your terms and/or use standard definitions then people will be able to follow your work and your results will mean something.

    However - as you progress in your science education you will find yourself putting your definitions in mathematical form rather than as short English language statements. The mathematical form of the definitions is much more useful than the "plain language" form.

    The definitions provide the material that we build physical models with.
  4. Jul 8, 2013 #3
    Memorizing definitions is useless. Useless. Useless. Useless.


    You should be understanding concepts and learning to apply them through problem solving.
  5. Jul 8, 2013 #4
    Your advice is contradictory. Your understanding of concepts would be very limited if you did not know the exact meaning of the things you are dealing with.
  6. Jul 8, 2013 #5

    Simon Bridge

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    That's a lot of waste :) ... however, how can you apply concepts without defining them?
    i.e. how can a student learn to understand "force" without the definition of force?.
    How can you communicate your ideas without agreeing on definitions.

    Memorizing definitions by itself is not useful to doing physics ... you still have to be able to, you know, do the physics. However, it is useful in the context of secondary education to get students used to being careful with their language.
  7. Jul 8, 2013 #6
    Nitpicking over memorizing and regurgitating exact definitions doesn't sound like physics to me. I don't think the important think is writing down what the concept is according to Webster.

    I might "know" that spin is intrinsic angular momentum carried by a particle that has no classical analog, but knowing that really doesn't help me understand spin at all.

    I think tests should focus on whether or not a student understands a concept rather than remembering a definition. the OP even says they never actually apply the concepts! What sort of physics is this?
  8. Jul 8, 2013 #7

    Simon Bridge

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    Oh I agree with you - however, the question in post #1 wasn't about the quality of the physics classes so much, which OP seems to understand pretty much blows, but about the role of definitions in physics.
  9. Jul 8, 2013 #8
    Yes. physics is taught the worst possible way. I hate my education system here. Remembering what is in textbook exactly is what is called "physics". Memorizing a problem is what they call physics! Doing experiment without understanding is what they call physics! Keeping silent without questioning when teacher is in class is physics! Getting good marks is physics! Afterall not understanding and doing physics is physics here!!!
  10. Jul 8, 2013 #9
    Yes this is not physics, A memory drill class
  11. Jul 8, 2013 #10
    Definitions are your building blocks. All statements, theorems, conjectures etc. depend on them. From a rigorous to a intuitive standpoint, they are absolutely essential as they provide the basic framework. That being said, I don't think it is necessarily a good idea to stress rote memorization. Personally, I find it much more useful to familiarize yourself with definitions through their application in exercises, proofs etc., so that one can truly grasp them.
  12. Jul 8, 2013 #11


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    yeah, as you say, definitions are important for maths. And a large part of physics is maths. And definition is important in physics too. For example I might start talking about mass in relativity. I might be talking about invariant mass or relativistic mass. These two things are totally different, so I must define what I mean when I say 'mass'.

    But I totally agree with what you're saying about memorizing definitions word for word being not a good way to study physics. It is mostly to give them a convenient way to test students. Even when you do spoken exam, the person asking you questions is hoping you answer in a certain way. So to some extent you will always have to 'waste' a bit of time, just to be able to learn the physics in the way the examiner wants to hear it, even though there may be other ways to explain it that are equally as valid.
  13. Jul 8, 2013 #12
    Yeah, I do agree with you that we waste our time by the learning method that the education system prescribes. In trying to memorize it word by word, we can solve problems, read more and gain some knowledge.. In mathematics exam, no problem will be given outside the textbook. Students omit the proofs of the formula and just memorize the problems.
    But, the saddest part is that such rote learning exams are used for admission to engineering in my place. If the future engineers are not ,made to think, how can they be engineers?
  14. Jul 8, 2013 #13


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    I hated this approach, and it plagued my science courses. I generally just went along with it, and sought out deeper meaning elsewhere. I had a very passionate and curious math teacher who would muddle around in some physics or chemistry topics with me in his spare time. Not that my science teacher didn't love science, but her degree was in biology but she taught ALL the science for our school.

    I disliked the definitions method towards teaching. But it was easy for her to prepare and grade, and also filled the gap between students who were strong and math, and those that were not. My friend's experiences in AP physics were obviously much different.

    Most of learning to think will fall on you anyways. Now is as good of time as any! Just pick up some interesting concepts and play with them. In time, you'll learn how you think. It just takes solving a lot of problems. And not just physics and math problems. I spend a lot of time solving puzzles and riddles, trying to say out-loud to myself my thought process. That helped me quite a bit.

    It get's better. Remember that generally, science teachers mean well. They just have to teach to certain standards and measures that don't cater to all.

  15. Jul 8, 2013 #14


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    For consistency in communication, following a convention is critical. Of course one has to remember definitions, and even formulae. That is inherent in mathematics, science, engineering and technology.

    Eventually one will apply force in solving physics problems. Initially, introductory textbooks familiarize students with terminology and concepts.

    Still, I prefer the method of providing mathematical background with the concepts. On the other hand, a good student goes beyond a single textbook. I usually would browse library stacks for other textbooks at the same level, or more advanced textbooks in order to look ahead. I did this since elementary school, since I didn't expect the teachers to do it for me.
  16. Jul 8, 2013 #15


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    Very wise words.

    Especially with internet what it is, you can readily find new material to learn from if you so choose. I suggest you get exceptionally good at sleuthing out new materials to dig into. It's nearly as important as actually reading it.
  17. Jul 8, 2013 #16

    Simon Bridge

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    I've seen this quite a bit - fortunately, in NZ anyway, it is a small minority of teachers who are like this and they quickly run into classroom management issues. (NZ kids are encouraged to question authority.)

    I've had blazing rows with heads of dept for setting exams where students will fail if they did not learn the particular mneumonics they tech in their classes for example.

    All you can do it whatever it takes to get the marks (sorry) and gain understanding outside the course (or change schools).

    Meantime I hope the original question has been answered.
  18. Jul 8, 2013 #17
    You can't change schools in my place easily in my place(state). I belong to India and India is divided into different states. Each state has different education board, a different method of testing, etc..
    My state has been worst hit in quality of education. There are no aptitude exams for admissions to colleges but only rote learning exams of the board.. It is a phenomenon of the state as some 800000 students attempt this exam out of which 500000 may belong to science(physics, chemistry and mathematics) stream.It is half a million and they are forced to learn this way!!
    Many cram schools are present which encourage students to memorize the whole textbook(grade 12) and vomit in exams to get 100% marks. They get the best colleges in my state.

    My interest was to compare the ideals of physics education in my state and the ideals of learning physics as suggested by other members of Physics Forum..I also wanted to know the importance of definitions in physics..
  19. Jul 8, 2013 #18


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    One of the big lessons in life that I've learned is that "the system" isn't necessarily set up in an optimal manner. We would like to believe that it is - that all instructors are competent, that the material is taught to us as efficiently as possible, that the material is up to date, that if we work hard in doing what we're told that we'll end up with a good career, etc.

    I think what you're discovering is that the system you're in is not optimal for you - and perhaps for anyone. Maybe it's set up that way because, as you've mentioned, there are a lot of students in India and that means there is a need for a lot of qualified teachers. And what do you do when there aren't enough to go around? One option is to simplify the teaching methods so that even someone who doesn't understand the material all that deeply can lead students through it, mark it, etc.

    I understand your frustrations. I sympathize. I hope that your system can improve. But realistically I think your best bet is to figure out how best to work within it to get to where you want to be. And while you do that, you can learn how you really learn best.
  20. Jul 9, 2013 #19

    Simon Bridge

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    Fair enough - it would probably be useful, then, for people to declare their jurisdictions.

    You can check out the NZ state education system online... including example exams:
  21. Jul 9, 2013 #20
    Thanks for the link. It was a bit helpful. It has subjective problem solving method and it evaluated the understanding of the student. These kind of exams should be used in school level.
  22. Jul 10, 2013 #21

    Simon Bridge

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    Those were all sample secondary school exams for NZ. The ones under "external" are set and assessed by a central authority - i.e. not the school or the school district.

    One of the things you can do is use other countries' resources to guide some self-study to compliment what your school wants you to do. The gain in understanding should help with the rote learning stuff too.
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