1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is planetary angular momentum

  1. Apr 6, 2015 #1
    Essentially just a consequence of inertia and gravity?
     
  2. jcsd
  3. Apr 6, 2015 #2

    phinds

    User Avatar
    Gold Member
    2016 Award

    Not sure what you mean by bringing gravity into it. Angular momentum is a consequence of rotation and mass, not rotation and weight.
     
  4. Apr 6, 2015 #3
    Then where does rotation come from? Gravity is the accelerating force right?
     
  5. Apr 6, 2015 #4

    phinds

    User Avatar
    Gold Member
    2016 Award

    The original gravitation attraction that cause matter to clump to form a planet or star brought in matter that was not all uniformly headed for the center of the mass accumulation, thus there was initial angular momentum, but I still think it's a stretch to say that gravity is directly responsible. It's the initial offset from pure radial infalling that causes the rotation / angular momentum. Gravity is quite capable of drawing in matter that is not offset from pure radial infalling, in which case there is no angular momentum, so how can you say it's gravity that is the cause?
     
  6. Apr 6, 2015 #5
    because momentum at this point can only be transferred right? then once the particles are bonded by gravity they wont have anywhere else to move but around Each other creating angular momentum. The same reason that gravity is the force that allows the Earth to be in constant acceleration. Inertia insures constant velocity while gravity changes direction.
     
  7. Apr 6, 2015 #6

    phinds

    User Avatar
    Gold Member
    2016 Award

    If I understand what you mean, then yes.

    I think your wording is weird but I think you get the idea

    .I'm not at all clear what you mean by all this.

    Gravity keeps the Earth from flying apart, angular momentum tries to get it to fly apart. Constant velocity is just because there is no force opposing constant velocity (forgetting for the moment the rather trivial contribution of the moon). I'm not sure where you think inertia comes in. Inertial is a consequence of the angular momentum, not a cause of the angular momentum.
     
  8. Apr 6, 2015 #7
    The law of inertia states that an object in motion stays at constant velocity unless a force acts on it and change in direction is a change in velocity is acceleration so in essence a spinning object is in constant acceleration. nd change in velocity is change in direction I wouldn't know how else to word it other than once bonded by gravity they would have no other place to transfer momentum thus producing angular momentum.
     
    Last edited: Apr 6, 2015
  9. Apr 7, 2015 #8

    jbriggs444

    User Avatar
    Science Advisor

    Yes. Perfectly correct
    A change in velocity does not necessarily involve a change in direction.
    Linear momentum is conserved. There is no need to "transfer" linear momentum into anything else. Angular momentum is conserved. It cannot be produced at all. If it is discovered to exist, it was always present. What gravity can do is bring moving bits of matter closer to one another so that the angular momentum that had always existed manifests as a higher spin rate -- like a figure skater bringing her arms in close.
     
    Last edited: Apr 7, 2015
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Is planetary angular momentum
  1. Angular momentum (Replies: 1)

  2. Angular momentum (Replies: 1)

  3. Angular Momentum (Replies: 1)

  4. Angular momentum (Replies: 1)

Loading...