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Is this why orbits happen?

  1. Jan 26, 2016 #1
  2. jcsd
  3. Jan 26, 2016 #2
    Without reading: yes, I do believe NASA is a credible source on how orbits work.

    With reading: yes, all of the information in the (NASA) article is factual. I haven't read the second link.
     
  4. Jan 26, 2016 #3

    A.T.

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  5. Jan 26, 2016 #4
    The reason I ask, is that a lot of people seem to say the momentum of the craft is not the reason it stays in orbit, but then NASA says it is, so... :)
     
  6. Jan 26, 2016 #5

    jbriggs444

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    Looking for a single thing to label as "the" cause for a given effect is not a prescription for understanding.
     
  7. Jan 26, 2016 #6

    russ_watters

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    Who says that? And: can you take what you learned in your other thread and apply it here?
     
  8. Jan 26, 2016 #7
    Well, I heard that if there's the forcebof gravity pulling it down, and momentums pushing it out, then the total force would be zero, and it would travel in a straight line
     
  9. Jan 26, 2016 #8

    jbriggs444

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    "I heard that" is not enough to give us a reference to refute. The typographical errors indicate that what you have written is not a direct quote. The fact that it is nonsensical suggests a garbled understanding. So we are left with little to do but ask for a better reference.
     
  10. Jan 26, 2016 #9
    Sorry for the long quote, but this guy on another thread responded to a similar question by saying,

    Mentor's note: Edited to give proper quote.
     
    Last edited by a moderator: Jan 26, 2016
  11. Jan 26, 2016 #10

    A.T.

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    There are better resources for learning basic physics, than those pop-sci NASA pages, which try to dumb it down until they stop making any sense.
     
  12. Jan 26, 2016 #11

    russ_watters

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    I don't see anything wrong in that quoted post, but it may be long enough that you're not absorbing it correctly. I'll try to be concise:

    In your other thread, you were told that inertia (mass) opposes an acceleration force (f=ma) and momentum (p=mv) is the cumulative sum of the force over time (f*t). For example, the larger the momentum, the more force and/or time is required to reverse the direction of motion.

    For projectile motion, a falling object gets pulled into a curved path by gravity. Per the description above, the higher the momentum - with a fixed gravitational force and object mass - the longer the force has to be applied in order to reverse its course. In other words, the faster the object moves, the less curved its path is. Make the object move fast enough and the curve matches the curvature of the Earth and you have an orbit.

    I sorta switched from momentum to velocity there without justifying it: In the situations we're describing, the force is already proportional to the object's mass, so the masses in the equations cancel. So in my opinion it is simpler to say an orbit depends on velocity, not momentum.
     
  13. Jan 26, 2016 #12
    Thanks a lot man, that actually makes sense :)
     
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