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Homework Help: Newton’s second law says F->net=ma-> So is ma-> force?

  1. Sep 23, 2015 #1
    1. The problem statement, all variables and given/known data
    Newton’s second law says F->net=ma->. So is ma-> a force? Explain.
    -> is a top bar arrow.

    2. Relevant equations
    F=ma or Fnet=ma

    3. The attempt at a solution
    (F) is a force and (m) is mass and (a) is acceleration. I don't really know what else this question is asking...
  2. jcsd
  3. Sep 24, 2015 #2


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    This smells to me like a question where some experts will disagree with others.
    Anyway, consider: suppose X is a physical quantity called a zerk. Don't worry about what a zerk is, I just made it up. Now you have an equation X=YZ, where Y and Z are two other types of physical entity.
    Is YZ necessarily a physical quantity of some type? Does this mean that YZ is a zerk? To put it another way, can a physical quantity of one type be equal to a physical quantity of another type?
  4. Sep 24, 2015 #3
    Yes like how pounds = kilograms but both are classified as "weight/mass units" instead of totally different unit types like length units vs mass/weight units. The equal sign does imply that they are equal but I don't think they are. Well wolfram alpha says this they are all physical quantities and force is a mass length unit per time^2 and together mass and acceleration equals a mass length unit per time^2. Therefore both are equal forces.
  5. Sep 24, 2015 #4


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    Pounds and kgs are unit systems for entities of the same type (mass). (Unless you mean to allow pounds force here, in which case pounds force cannot be equated to kgs).
    But I agree with your conclusion, that ma is a force. My caution is that the question setter might argue that there is no actual force ma in the physical context. I hope not. By that argument, a resultant force would not be a force either.
  6. Sep 24, 2015 #5
    Yeah I said mass/weight not lbsF or ftlbs or inchlbs.
    Good that you agree and thanks again for your help. Nah the teacher seems okay when you have a basic understanding and attempt to do ALL the work assigned vs not doing it. It doesn't have to be correct as long as it is backed up by something reasonable.
  7. Sep 25, 2015 #6
    This seems like an interesting question. Since I'm just a rookie in Physics, I don't know how to give 'force' any meaningful interpretation. I can only describe it using dimensional analysis, which inevitably makes me answer that 'force' is (ontologically and metaphysically, if that makes sense) exactly the same thing as 'mass times acceleration'. Actually, what meaningful interpretation could there even be of "m*a"?

    I am sensing that I am VERY confused!
  8. Sep 26, 2015 #7


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    Most basic Physical concepts originate in observation and senses. You see the difference between light and dark, and human brain created the concept "light", without knowing, what light really is. You hear things, from this sense came the concept of sound. You feel something when you hit or push or pull an other body: From this feeling came the concept of force, "interaction between objects". It is observed that stretching out or compressing a spring needs force. If you compress the same spring with the same length you feel the same "force". If you connect a body to the compressed spring and release, the body will accelerate. If you halve the body its acceleration is twice it was before. It was concluded from many observations that the force is proportional to the acceleration it causes. F=ma, and m is defined as the factor of proportionality: m=F/a.
    The unit of mass was chosen and the standard, the kilogram was made, along with a lot of copies. The mass of other objects can be determined by comparing the acceleration caused by the same force on the standard kg and on the unknown mass.
    On the other hand, if you know the mass m of an object and see it accelerating with acceleration a, you know that the net force acting on the object is F=ma.
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