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Why is inertia not stopping acceleration?

  1. May 24, 2015 #1
    Inertia is the resistance of any physical object to any change in its state of motion, including changes to its speed and direction.
    It is kind of counterforce which is resisting the change of speed.
    But when there is this counterforce which is at the same level as force causing the acceleration, why is acceleration actually possible? Is this because there is some time lag between force causing acceleration and inertia counterforce? Have there been some experiments about this topic?
    Or is there some other explanation? But what I know, cause of inertia itself have not been explained yet.
  2. jcsd
  3. May 24, 2015 #2


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    Staff: Mentor

    This "counterforce" is not a force, which is exactly the misconception here.
    You need force to get acceleration, done.
  4. May 24, 2015 #3


    Staff: Mentor

    In an inertial frame there is no counterforce.
  5. May 24, 2015 #4
    Inertia is not a kind of counterforce. It is a measure of how hard it is to change an object's speed and direction(thus its acceleration).
    From Newton's second law F = ma, we can see that inertia is proportional to the object's mass. For example, it is harder to change a train's motion than to change a car's motion.
  6. May 24, 2015 #5
    OK, we can agree, that you all are saying that inertia is not counterforce and Im saying that it is. You are simply stating the mainstream opinion a thats it for you, no need to think about it more deeply.

    But I guess we can all agree, that you dont know what inertia is and what is causing it.
    Im trying to develop some theory explaining it and Im searching for experiments which would help me to explain it.

    I know, that for example, there were detailed experiments about Equivalence principle between gravity mass and inertial mass. But have there been some detailed experiments about mass and acceleration, maybe extremely detailed time line of acceleration?
    So IF inertia would be some kind of counterforce, mathematically it would be still the same F=ma, but maybe there would be some implications, like there would be some time lag between force and counterforce. This could also mean that maybe there would be also some time lag between force and acceleration. Were there some experiments about this topic? Or is there maybe some acceleration-quantum behavior? Like steps in acceleration time line which would be caused by feedback loop force-acceleration-counterforce?
  7. May 24, 2015 #6


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    No, they are saying something that they understand and you don't because you are the one asking about a difficulty that arises from your understanding of it.

    I'm sorry, did you actually intend to use the word "you" here?

    Actually, yes, starting with Gallileo, about 400 years ago.

    Yes, again about 400 years of such experiments.

    [quote\ Or is there maybe some acceleration-quantum behavior? Like steps in acceleration time line which would be caused by feedback loop force-acceleration-counterforce?[/QUOTE]
    Perhaps if you learned some basic physics first, you wouldn't have to ask such elementary questions. It also might be a good idea NOT to insult the people you are asking by making assertions about what they do or do not know.
  8. May 24, 2015 #7
    I think it is pretty well known what inertia is.
    This is basically the definition I was taught.

    Your current attitude towards physics will do you no favors, Spider. I think everyone in this thread knows significantly more physics than you or me. Sometimes you just have to accept some things at face value even if it does not instantly make sense to you.
  9. May 24, 2015 #8


    Staff: Mentor

    That is not the purpose of this forum. Thread closed.
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