3 ms·

How F = ma Could Break Down at Low Accelerations

27 points by troystribling 17y ago

ajross 17y ago
This isn't a new result. It's just a poorly-explained pop-science review article on MOND: http://en.wikipedia.org/wiki/MOND http://en.wikipedia.org/wiki/MOND It's one of those things that looks just awful aesthetically, but explains a few things (galactic-scale mechanics in this case) for which we don't currently have good answers. Wikipedia is a better source. This article is mostly fluff.
- randallsquared 17y ago
  "But today, Milgrom says that he has calculated a new effect of MOND that should be measurable for planets and comets in the solar system," they say, so apparently there is something new to this.
- scott_s 17y ago
  I think you judged it too fast. The article spends most of its words explaining MOND because that's necessary to present the new result: But today, Milgrom says that he has calculated a new effect of MOND that should be measurable for planets and comets in the solar system. The new effect is a quadropole force that repels objects in the space above and below the plane of the solar system while attracting objects that lie within the plane. Milgrom says that this should produce an effect on the precession of the perihelion of planets in the solar system. The paper in question, http://uk.arxiv.org/abs/0906.4817 http://uk.arxiv.org/abs/0906.4817, is dated June 25, 2009. I'm not a physicist, but it's clear to me that Milgrom's contribution is a MOND prediction that can be tested experimentally.
- profquail 17y ago
  Not to mention that F = ma is just a simplification used in entry-level physics classes. The real formula is F = dp/dt, or F = m(dv/dt) + v(dm/dt), which is sometimes called the "rocket equation" (since rockets burn their fuel to accelerate, they don't have a constant mass). And, he said it's the cornerstone of modern physics; not to be pedantic, but Newton's laws are usually called 'classical physics', while the term 'modern physics' is saved for quantum theory and relativity (check your local university's physics course catalog). Reference: http://en.wikipedia.org/wiki/Force#Newton.27s_second_law http://en.wikipedia.org/wiki/Force#Newton.27s_second_law
  - troystribling 17y ago
    F=dp/dt is true in quantum mechanics and relativity as well as classical mechanics.
    - joeyo 17y ago
      Provided you are in an inertial reference frame.
deleted 17y ago
[deleted]

27 points by troystribling 17y ago

This isn't a new result. It's just a poorly-explained pop-science review article on MOND: http://en.wikipedia.org/wiki/MOND http://en.wikipedia.org/wiki/MOND It's one of those things that looks just awful aesthetically, but explains a few things (galactic-scale mechanics in this case) for which we don't currently have good answers. Wikipedia is a better source. This article is mostly fluff.

randallsquared 17y ago
"But today, Milgrom says that he has calculated a new effect of MOND that should be measurable for planets and comets in the solar system," they say, so apparently there is something new to this.
scott_s 17y ago
I think you judged it too fast. The article spends most of its words explaining MOND because that's necessary to present the new result: But today, Milgrom says that he has calculated a new effect of MOND that should be measurable for planets and comets in the solar system. The new effect is a quadropole force that repels objects in the space above and below the plane of the solar system while attracting objects that lie within the plane. Milgrom says that this should produce an effect on the precession of the perihelion of planets in the solar system. The paper in question, http://uk.arxiv.org/abs/0906.4817 http://uk.arxiv.org/abs/0906.4817, is dated June 25, 2009. I'm not a physicist, but it's clear to me that Milgrom's contribution is a MOND prediction that can be tested experimentally.
profquail 17y ago
Not to mention that F = ma is just a simplification used in entry-level physics classes. The real formula is F = dp/dt, or F = m(dv/dt) + v(dm/dt), which is sometimes called the "rocket equation" (since rockets burn their fuel to accelerate, they don't have a constant mass). And, he said it's the cornerstone of modern physics; not to be pedantic, but Newton's laws are usually called 'classical physics', while the term 'modern physics' is saved for quantum theory and relativity (check your local university's physics course catalog). Reference: http://en.wikipedia.org/wiki/Force#Newton.27s_second_law http://en.wikipedia.org/wiki/Force#Newton.27s_second_law
- troystribling 17y ago
  F=dp/dt is true in quantum mechanics and relativity as well as classical mechanics.
  - joeyo 17y ago
    Provided you are in an inertial reference frame.

deleted 17y ago

[deleted]